Post Traumatic Stress DisorderPhase 3STOPNCT06412757
Silexan in the Treatment Of Posttraumatic Stress Disorder Trial
A Phase 3 study testing Silexan in people with Post Traumatic Stress Disorder, run by Deakin University at 4 sites in Australia.
Trial summary
Posttraumatic stress disorder (PTSD) is a common and debilitating mental illness. Current treatments for PTSD include psychotherapy and antidepressant medications. Many patients are unable to tolerate psychotherapy for PTSD and drop out of it. In addition, its effectiveness is limited. Read more about this study
- Who is it for?
- Ages 18 years and older
- Conditions the study is for
- Post Traumatic Stress Disorder
- What is being tested?
- Silexan
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 278 participants
- Where
- 4 sitesAustralia
- Study dates
- 26 Aug 2024to Jun 2027
- Phase
- Phase 3
- Are there results?
- Not yet: the study is under way
Key requirements
Who can take part, as listed by the sponsor. Only the study team can confirm whether you are eligible, so take this list to your doctor.
- Ages 18 years and older
- All sexes
- No healthy volunteers
- Adult, Older adult
Who may be able to join
- Aged 18 years or over.
- Fluent in English.
- Meet DSM-5 criteria for PTSD, irrespective of occupation (e.g. first responder, police officer, ex-military or civilian), determined using the Mini International Neuropsychiatric Interview 7.0.2.
- Have a score on the PTSD Checklist for DSM-5 (PCL-5) equal to or over 33.
Who cannot join
- Are currently serving in the Australian Defence Force
- Lifetime history of a psychotic or bipolar disorder, or dissociative identity disorder.
- Moderate or severe alcohol or other substance use disorder within 3 months of screening.
- Active suicidal or homicidal ideation.
- Borderline Personality Disorder (BPD).
- Acute or unstable medical illness or other significant medical condition, that would make participation in the trial unsafe or inappropriate.
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- Pregnancy, lactation or unwillingness to use an acceptable method of contraception (required for both males and females who are of reproductive potential and sexually active with partners of the opposite sex) through the duration of participants' involvement in the study up to and including week 16. Participants will also be advised not to donate eggs or sperm during the study period.
- Commencement of a trauma-focussed psychotherapy (including Prolonged Exposure, Cognitive Processing Therapy and Eye Movement Desensitisation and Reprocessing) within 3 months of screening.
- Commencement or change in dose of psychoactive medications within 4 weeks of screening.
- Participants will be asked not to initiate psychotherapy or change the dose of psychoactive medications during the course of the study except in clinically urgent circumstances; if this becomes necessary, a decision will be made on a case-by-case basis with regard to retaining the participant or terminating their participation.
- Severe acquired brain injury.
- Individual is not eligible for public mental health services due to their visa status in Australia or for any other reason.
- Any other condition that in the opinion of the research team is likely to make completion of the trial requirements infeasible.
- Inability to understand or speak English to the extent necessary to give informed consent and complete the trial (researcher or clinician-determined).
Trial locations and contacts
4 sites in 1 country. Contact the study team or a site near you to ask about taking part.
Australia4 sites, 4 recruiting
- Recruiting
University of Melbourne
Carlton, Victoria, 5053
Meaghan O'Donnell, MPsych, PhD, (03) 9035 7883, mod@unimelb.edu.au
- Recruiting
Deakin University
Geelong, Victoria, 3220
Michael Berk, MMed(Psych), FF(Psych)SA, PhD, (03) 4215 3320, michael.berk@deakin.edu.au
- Recruiting
Austin Health
Heidelberg, Victoria, 3084
Richard Kanaan, CTT, MBBCH, PhD, (03) 9496 3351, richard.kanaan@unimelb.edu.au
- Recruiting
Ramsay Clinic Albert Road
Melbourne, Victoria, 3004
Malcom Hopwood, MBBS, MPM, MD, (03) 9279 3518, mhopwood@unimelb.edu.au
About this study
Official title: Silexan in the Treatment Of Posttraumatic Stress Disorder (STOP) Trial
Posttraumatic stress disorder (PTSD) is a common and debilitating mental illness. Current treatments for PTSD include psychotherapy and antidepressant medications. Many patients are unable to tolerate psychotherapy for PTSD and drop out of it. In addition, its effectiveness is limited. Up to 50 percent of patients who receive psychotherapy do not benefit from it. Antidepressant medications have only small benefits in PTSD. They also have unpleasant side effects that can make patients unwilling to take them. There is an urgent need to develop new treatments for PTSD that work and are well-tolerated. Silexan has the potential to provide an important alternative treatment for PTSD.
Silexan is derived from lavender oil. It is taken orally in the form of capsules. It is currently available over-the-counter in 14 countries, including Australia and the United States. Previous research has shown that it is an effective treatment for anxiety disorders, including Generalized Anxiety Disorder. It is also well-tolerated by patients. The only side effects that have been identified so far are mild gastrointestinal symptoms (including burping and breath odour) and these are uncommon. The results of a small pilot study suggest that Silexan may also be effective and well-tolerated in PTSD.
Read more
The STOP trial is a clinical trial that aims to investigate whether adding Silexan to treatment-as-usual improves PTSD symptoms in adults with PTSD. The trial will recruit 278 participants. Participants will be randomly assigned to take Silexan or a placebo (look-alike dummy pills) daily in addition to their usual medications for 12 weeks. The severity of their PTSD symptoms will be assessed prior to and at the end of this 12-week period.
The STOP trial has the potential to obtain definitive evidence regarding whether Silexan helps treat symptoms of PTSD. If Silexan is found to be an effective treatment for PTSD, the pool of patients who could potentially benefit from this treatment includes any adults with PTSD. Silexan is already available over-the-counter at a relatively low cost so there will be few barriers to accessing this treatment.
Read the detailed description
Background: Posttraumatic stress disorder (PTSD) is a common and debilitating psychiatric disorder. Existing PTSD treatments have very significant limitations. Current evidence-based treatments for PTSD include trauma-focussed psychotherapy and antidepressant medications, including selective serotonin reuptake inhibitors and the serotonin noradrenaline reuptake inhibitor venlafaxine. Many patients are unable to tolerate trauma-focussed psychotherapy. Uptake is relatively low and dropout rates are high. In addition, up to 50% of patients fail to respond to this therapy. Antidepressant medications have small clinical effects and are associated with unpleasant side effects that can lead to non-adherence. There is an urgent need for new treatments for PTSD that are effective and well-tolerated. Silexan has the potential to provide a transformative alternative to these treatments. It is an orally administered lavender oil preparation whose main constituents are the monoterpenoids linalool and linalyl acetate. It is available over-the-counter in 14 countries, including Australia and the United States. It has a novel pharmacodynamic profile that includes potent inhibition of voltage-gated calcium channels and reduction of serotonin 1A receptor binding potential. Silexan is an effective treatment for Generalized Anxiety Disorder (GAD) and other anxiety disorders. A 2019 independent meta-analysis of data from five randomized controlled trials involving 1,320 participants with anxiety disorders found that Silexan 160 mg out-performed paroxetine and lorazepam in reducing anxiety symptoms. Silexan is also well-tolerated. The only adverse effects that have been identified so far are mild gastrointestinal symptoms and these are uncommon. Promising pilot data suggest that Silexan may also be effective and well-tolerated in PTSD.
Hypothesis: The primary hypothesis is that Silexan, as an adjunct to treatment-as-usual, over 12 weeks will be superior to placebo in improving PTSD symptoms in adults with PTSD.
Specific aims: The trial aims to investigate the effectiveness of adjunctive Silexan, compared with placebo, over 12 weeks in improving PTSD symptoms. The primary outcome measure will be the between-group change from baseline in the total symptom severity score on the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5).
Study design: The trial is a phase 3, 12-week, multi-site, parallel-arm, randomized, placebo-controlled, double-blind trial. Participants will be adults with PTSD without comorbid psychosis, bipolar disorder, moderate or severe substance use disorder or Borderline Personality Disorder. Participants randomized to the Silexan arm will receive Silexan 160 mg daily for 12 weeks in addition to their usual prescribed medications. Participants randomized to the placebo arm will receive capsules containing an inert placebo. The target sample size will be 250 participants, or 125 per arm. The study will recruit 278 participants to account for a 10% drop-out rate.
Clinical impact: There is an urgent need to develop new treatments for PTSD that are effective and well-tolerated. This trial has the potential to provide definitive evidence of the efficacy of Silexan in adult PTSD. Silexan is safe, well-tolerated, currently available and affordable, facilitating a rapid translation into clinical care. If Silexan is found to be an effective treatment for PTSD, the pool of patients who could potentially benefit from this treatment includes any adults with PTSD.
- Conditions
- Post Traumatic Stress Disorder
- Being tested
- Silexan, Placebo
- Keywords
- posttraumatic stress disorder, adjunctive treatment, Silexan, phytoceutical, pharmacotherapy, randomized controlled trial
- Medical subject headings
- Stress Disorders, Post-Traumatic
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
SilexanDrug
Participants in the Silexan arm will take two over-encapsulated capsules, each containing 80 mg Silexan, daily orally in the morning in addition to their usual medications. No modifications of allocated interventions will be made for any trial participants; if appropriate (i.e following the emergence of adverse events) participants will be withdrawn from the intervention.
PlaceboOther
Participants in the placebo arm will take two capsules containing an inert placebo daily orally in the morning in addition to their usual medications. The placebo capsules will contain a sub-therapeutic amount of lavender oil to mimic the odor of the experimental drug (Silexan).
| Study group | Role | What they receive |
|---|---|---|
| Silexan 160 mg | Experimental | Participants in the Silexan arm will take Silexan 160 mg daily in the morning for 12 weeks in addition to their usual prescribed psychoactive medications. Participants will be followed up at 2, 4, 6, 8 and 12 weeks of the intervention period, as well as at 4 weeks post-treatment (off-treatment follow-up period). Receives: Drug: Silexan |
| Placebo | Placebo comparator | Participants in this arm will take two placebo capsules daily in the morning for 12 weeks in addition to their usual medications. Participants will be followed up at 2, 4, 6, 8 and 12 weeks of the intervention period, as well as at 4 weeks post-treatment (off-treatment follow-up period). Receives: Other: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
Clinician-Administered PTSD Scale for DSM-5 (CAPS-5)
The Primary Outcome Measure will be the between-group difference in the change from baseline to week 12 in the total symptom severity score on the CAPS-5. The CAPS-5 has good internal consistency, inter-rater reliability, test-retest reliability and convergent validity in measuring PTSD symptom severity, and is regarded as the gold-standard for measuring PTSD symptoms in research settings. The CAPS-5 will be used to query the presence of PTSD symptoms across the two weeks prior to each CAPS-5 assessment. We will also compare between-group differences in remission rates of PTSD, as determined by the CAPS-5.
Measured: At baseline and at week 12 of the study period
Secondary outcomes (19)
Hamilton Anxiety Rating Scale (HAM-A)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of anxiety symptoms on the HAM-A. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Hamilton Anxiety Rating Scale consists of 14 items and is the most widely used interview instrument for measurement of anxiety in adults and children.
Measured: At baseline, at week 12 and at week 16 of the study period
Generalized Anxiety Disorder-7 (GAD-7)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of anxiety symptoms on the GAD-7. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Generalized Anxiety Disorder-7 is a 7-item scale with each item scores on a scale of 0 ("not at all") to 3 ("nearly every day") based on symptom presentation in the past two weeks.
Measured: At baseline, at week 12 and at week 16 of the study period
Generalized Anxiety Disorder-7 (GAD-7)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of anxiety symptoms on the GAD-7, measured at baseline, week 4, week 8 and week 12 of treatment. The Generalized Anxiety Disorder-7 is a 7-item scale with each item scores on a scale of 0 ("not at all") to 3 ("nearly every day") based on symptom presentation in the past two weeks.
Measured: At baseline, week 4, week 8 and week 12 of the study period
Beck Depression Inventory-II (BDI-II)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of depressive symptoms on the BDI-II. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The BDI-II comprises of 21 questions rated on 4-point scales of severity (0-3), with a total score that reflects the level or degree of depression. The BDI-II has high internal consistency.
Measured: At baseline, at week 12 and at week 16 of the study period
Patient Health Questionnaire-9 (PHQ-9)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of depressive symptoms on the PHQ-9. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Patient Health Questionnaire-9 is a screening measure of depressive symptoms. The PHQ-9 asks participants to rate each of the 9 DSM-IV criteria for major depressive disorder from 0 ("not at all") to 3 ("nearly every day").
Measured: At baseline, at week 12 and at week 16 of the study period
Patient Health Questionnaire-9 (PHQ-9)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of depressive symptoms on the PHQ-9, measured at baseline, week 4, week 8 and week 12 of treatment. The Patient Health Questionnaire-9 is a screening measure of depressive symptoms. The PHQ-9 asks participants to rate each of the 9 DSM-IV criteria for major depressive disorder from 0 ("not at all") to 3 ("nearly every day").
Measured: At baseline, week 4, week 8 and week 12 of the study period
Patient Health Questionnaire-15 (PHQ-15)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of somatic symptoms on the PHQ-15. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Patient Health Questionnaire-15 is a Patient Health Questionnaire module designed to assess the presence of somatic symptoms. The PHQ-15 has good internal consistency and test-retest reliability.
Measured: At baseline, at week 12 and at week 16 of the study period
Patient Health Questionnaire-15 (PHQ-15)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of somatic symptoms on the PHQ-15, measured at baseline, week 4, week 8 and week 12 of treatment. The Patient Health Questionnaire-15 is a Patient Health Questionnaire module designed to assess the presence of somatic symptoms. The PHQ-15 has good internal consistency and test-retest reliability.
Measured: At baseline, week 4, week 8 and week 12 of the study period
Pittsburgh Sleep Quality Index, with Addendum for PTSD (PSQI & PSQI-A)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of sleep quality on the PSQI \& PSQI-A. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Pittsburgh Sleep Quality Index is designed to measure overall sleep quality during the previous month in a clinical population. The PSQI comprises 19 questions across 7 domains or "component" scores, each weighted equally on a 0-3 scale. The PSQI will include the PTSD Addendum (PSQI-A), which are 10 additional questions designed to assess the frequency of disruptive nocturnal behaviours.
Measured: At baseline, at week 12 and at week 16 of the study period
Pittsburgh Sleep Quality Index, with Addendum for PTSD (PSQI & PSQI-A)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of sleep quality on the PSQI \& PSQI-A, measured at baseline, week 4, week 8 and week 12 of treatment. The Pittsburgh Sleep Quality Index is designed to measure overall sleep quality during the previous month in a clinical population. The PSQI comprises 19 questions across 7 domains or "component" scores, each weighted equally on a 0-3 scale. The PSQI will include the PTSD Addendum (PSQI-A), which are 10 additional questions designed to assess the frequency of disruptive nocturnal behaviours.
Measured: At baseline, week 4, week 8 and week 12 of the study period
Alcohol Use Disorders Identification Test (AUDIT)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of problematic alcohol use on the AUDIT. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Alcohol Use Disorders Identification Test is a 10-item questionnaire developed through a 6-country World Health Organization collaborative project, as a screening tool for harmful alcohol consumption. The AUDIT spans the domains of alcohol consumption, drinking behaviour, and alcohol-related problems that may have occurred in the past year, as well as lifetime exposure.
Measured: At baseline, at week 12 and at week 16 of the study period
Alcohol Use Disorders Identification Test (AUDIT)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of problematic alcohol use on the AUDIT, measured at baseline, week 4, week 8 and week 12 of treatment. The Alcohol Use Disorders Identification Test is a 10-item questionnaire developed through a 6-country World Health Organization collaborative project, as a screening tool for harmful alcohol consumption. The AUDIT spans the domains of alcohol consumption, drinking behaviour, and alcohol-related problems that may have occurred in the past year, as well as lifetime exposure.
Measured: At baseline, week 4, week 8 and week 12 of the study period
World Health Organization (WHO) Disability Assessment Schedule (WHODAS 2.0)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of functional disability on the WHODAS 2.0. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The 12-item self-report version of the World Health Organization (WHO) Disability Assessment Schedule is a measure of functioning and disability across six major life domains due to health conditions. The WHODAS has high internal consistency and test-retest reliability.
Measured: At baseline, at week 12 and at week 16 of the study period
General Well Being Schedule (GWBS)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of general well-being on the GWBS. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The General Well Being Schedule is an 18-item measure of subjective psychological well-being and distress. The GWBS has good test-retest reliability, as well as internal consistency for both sexes.
Measured: At baseline, at week 12 and at week 16 of the study period
Assessment of Quality of Life-6D (AQoL-6D)
One of the Secondary Outcome Measures will be the between-group difference in the change from baseline to week 12, and baseline to week 16 (while including all available time-points including the off-treatment period) in measures of quality of life on the AQoL-6D. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The Assessment of Quality of Life-6D scale is a 20-item, 6-dimensional measure with each item containing between 4 and 6 response levels. The AQoL-6D assesses the following 6 domains of quality of life: Independent Living, Relationships, Mental Health, Coping, Pain and Senses.
Measured: At baseline, at week 12 and at week 16 of the study period
PTSD Checklist for DSM-5 (PCL-5)
One of the Secondary Outcome Measures will be the will be the between-group difference in the change from intake to week 12, and intake to week 16 (while including all available time-points including the off-treatment period) in measures of quality of life on the PCL-5. Additional comparisons for between-group differences from week 12 to week 16 will also be performed. The PTSD Checklist for DSM-5 is a 20-item self-report measure that assesses the presence and intensity of each of the 20 DSM-5 PTSD symptoms. The PCL-5 has been shown to have strong reliability and validity. A score of ≥ 33 suggests PTSD.
Measured: At intake, at week 12 and at week 16 of the study period
PTSD Checklist for DSM-5 (PCL-5)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of PTSD symptom severity on the PCL-5, measured at intake, and at week 2, week 4, week 6, week 8 and week 12 of treatment. The PTSD Checklist for DSM-5 is a 20-item self-report measure that assesses the presence and intensity of each of the 20 DSM-5 PTSD symptoms. The PCL-5 has been shown to have strong reliability and validity. A score of ≥ 33 suggests PTSD.
Measured: At intake, week 2, week 4, week 6, week 8 and week 12 of the study period
Patient Global Impression of Change Scale (PGIC)
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of patient global impression of change on the PGIC, measured at week 2, week 4, week 6, week 8 and week 12 of treatment. The Patient Global Impression of Change Scale asks participants to rate the change (if any) that they have experienced since starting treatment, on a scale of 1 ("No change") to 7 ("A great deal better and a considerable improvement that has made all the difference").
Measured: Week 2, week 4, week 6, week 8 and week 12 of the study period
Actigraphy watches
One of the Secondary Outcome Measures will be the longitudinal trajectory analysis of sleep, actigraphy, and physiological measures (including mean heart rate, mean heart rate variability, mean blood pressure), measured continuously throughout the study period (baseline to week 16).
Measured: Continously from baseline until week 16 of the study period
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted14 May 2024
- Study start26 Aug 2024
- Primary completionMay 2027 (estimated)
- Study completionJun 2027 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Publications (1)Papers the sponsor has linked to this study.
- Other trials for Post Traumatic Stress DisorderStudies of the same condition, open and under way.
- What the trial phases meanHow a treatment moves from first tests in people to approval.
More details
For doctors and researchers: how the study is designed, who runs it, and its registry IDs.
Study design
- Study type
- Interventional
- Phase
- Phase 3
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- The trial is a phase 3, 12-week, parallel-arm, randomized, placebo-controlled, double-blind trial. Participants will be randomly allocated to receive either (a) Silexan 160 mg or (b) an identical appearing inert placebo, daily for 12 weeks in addition to their usual prescribed medications.
- Masking
- Quadruple blind
- Who is masked
- Participant, Care provider, Investigator, Outcomes assessor
- Enrolment
- 278 participants (estimated)
Sponsor and investigators
- Lead sponsor
- Deakin University
- Sponsor type
- University, hospital or other
- Collaborators
- University of Melbourne, Ramsay Clinic Albert Road
- Responsible party
- Principal investigator, Gregory Roebuck, Deakin University
- Investigators
- Michael Berk, PhD, Principal investigator, Deakin University
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT06412757
- Sponsor's protocol ID
- 29307
- Other IDs
- HT9425-23-1-0885
- Acronym
- STOP
- Status last verified
- Dec 2025
- First submitted
- 9 May 2024
- Last updated
- 18 Dec 2025
- Results posted
- No
- Data monitoring committee
- Yes
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: The National Institute of Mental Health Data Archive (NDA) will be used as an online data-sharing repository. De-identified participant data will be linked in the shared data repository using an assigned NDA Global Unique Identifier (GUID). The GUID itself is not personally identifiable information or protected health information.
Publications
Roebuck G, Parkin GM, O'Donnell M, Khanna R, Forbes D, Lau W, Serpell S, Al-Azzawi H, Santamaria E, Mohebbi M, Iyer R, Dean O, Kanaan RA, Hopwood M, Green JE, Berk M. The Silexan in the Treatment Of Posttraumatic stress disorder (STOP) trial: protocol for a 12-week randomised controlled trial of adjunctive Silexan for PTSD. BMC Complement Med Ther. 2026 Feb 24;26(1):122. doi: 10.1186/s12906-026-05312-7.
PubMed 41736003
Study at a glance
From the registry record, last updated by the sponsor on 18 Dec 2025. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- Silexan in the Treatment Of Posttraumatic Stress Disorder (STOP) Trial
- ClinicalTrials.gov ID
- NCT06412757
- Acronym / sponsor ID
- STOP / 29307
- Conditions
- Post Traumatic Stress Disorder
- Keywords
- posttraumatic stress disorder, adjunctive treatment, Silexan, phytoceutical, pharmacotherapy, randomized controlled trial
- Phase
- Phase 3
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 278 participants (estimated)
- Lead sponsor
- Deakin UniversityUniversity, hospital or other
- Collaborators
- University of Melbourne, Ramsay Clinic Albert Road
- Study start
- 26 Aug 2024 (actual)
- Primary completion
- May 2027 (estimated)
- Study completion
- Jun 2027 (estimated)
- First posted
- 14 May 2024 (actual)
- Results
- Not posted in the source record
Clinical summary
The research question as the sponsor registered it. This describes what the study plans to test, not what it found.
Posttraumatic stress disorder (PTSD) is a common and debilitating mental illness. Current treatments for PTSD include psychotherapy and antidepressant medications. Many patients are unable to tolerate psychotherapy for PTSD and drop out of it. In addition, its effectiveness is limited. Up to 50 percent of patients who receive psychotherapy do not benefit from it. Antidepressant medications have only small benefits in PTSD. They also have unpleasant side effects that can make patients unwilling to take them. There is an urgent need to develop new treatments for PTSD that work and are well-tolerated. Silexan has the potential to provide an important alternative treatment for PTSD.
Silexan is derived from lavender oil. It is taken orally in the form of capsules. It is currently available over-the-counter in 14 countries, including Australia and the United States. Previous research has shown that it is an effective treatment for anxiety disorders, including Generalized Anxiety Disorder. It is also well-tolerated by patients. The only side effects that have been identified so far are mild gastrointestinal symptoms (including burping and breath odour) and these are uncommon. The results of a small pilot study suggest that Silexan may also be effective and well-tolerated in PTSD.
The STOP trial is a clinical trial that aims to investigate whether adding Silexan to treatment-as-usual improves PTSD symptoms in adults with PTSD. The trial will recruit 278 participants. Participants will be randomly assigned to take Silexan or a placebo (look-alike dummy pills) daily in addition to their usual medications for 12 weeks. The severity of their PTSD symptoms will be assessed prior to and at the end of this 12-week period.
The STOP trial has the potential to obtain definitive evidence regarding whether Silexan helps treat symptoms of PTSD. If Silexan is found to be an effective treatment for PTSD, the pool of patients who could potentially benefit from this treatment includes any adults with PTSD. Silexan is already available over-the-counter at a relatively low cost so there will be few barriers to accessing this treatment.
Detailed description
Background: Posttraumatic stress disorder (PTSD) is a common and debilitating psychiatric disorder. Existing PTSD treatments have very significant limitations. Current evidence-based treatments for PTSD include trauma-focussed psychotherapy and antidepressant medications, including selective serotonin reuptake inhibitors and the serotonin noradrenaline reuptake inhibitor venlafaxine. Many patients are unable to tolerate trauma-focussed psychotherapy. Uptake is relatively low and dropout rates are high. In addition, up to 50% of patients fail to respond to this therapy. Antidepressant medications have small clinical effects and are associated with unpleasant side effects that can lead to non-adherence. There is an urgent need for new treatments for PTSD that are effective and well-tolerated. Silexan has the potential to provide a transformative alternative to these treatments. It is an orally administered lavender oil preparation whose main constituents are the monoterpenoids linalool and linalyl acetate. It is available over-the-counter in 14 countries, including Australia and the United States. It has a novel pharmacodynamic profile that includes potent inhibition of voltage-gated calcium channels and reduction of serotonin 1A receptor binding potential. Silexan is an effective treatment for Generalized Anxiety Disorder (GAD) and other anxiety disorders. A 2019 independent meta-analysis of data from five randomized controlled trials involving 1,320 participants with anxiety disorders found that Silexan 160 mg out-performed paroxetine and lorazepam in reducing anxiety symptoms. Silexan is also well-tolerated. The only adverse effects that have been identified so far are mild gastrointestinal symptoms and these are uncommon. Promising pilot data suggest that Silexan may also be effective and well-tolerated in PTSD.
Hypothesis: The primary hypothesis is that Silexan, as an adjunct to treatment-as-usual, over 12 weeks will be superior to placebo in improving PTSD symptoms in adults with PTSD.
Specific aims: The trial aims to investigate the effectiveness of adjunctive Silexan, compared with placebo, over 12 weeks in improving PTSD symptoms. The primary outcome measure will be the between-group change from baseline in the total symptom severity score on the Clinician-Administered PTSD Scale for DSM-5 (CAPS-5).
Study design: The trial is a phase 3, 12-week, multi-site, parallel-arm, randomized, placebo-controlled, double-blind trial. Participants will be adults with PTSD without comorbid psychosis, bipolar disorder, moderate or severe substance use disorder or Borderline Personality Disorder. Participants randomized to the Silexan arm will receive Silexan 160 mg daily for 12 weeks in addition to their usual prescribed medications. Participants randomized to the placebo arm will receive capsules containing an inert placebo. The target sample size will be 250 participants, or 125 per arm. The study will recruit 278 participants to account for a 10% drop-out rate.
Clinical impact: There is an urgent need to develop new treatments for PTSD that are effective and well-tolerated. This trial has the potential to provide definitive evidence of the efficacy of Silexan in adult PTSD. Silexan is safe, well-tolerated, currently available and affordable, facilitating a rapid translation into clinical care. If Silexan is found to be an effective treatment for PTSD, the pool of patients who could potentially benefit from this treatment includes any adults with PTSD.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- Quadruple blind (participant, care provider, investigator, outcomes assessor)
- Number of arms
- 2
- Model description
- The trial is a phase 3, 12-week, parallel-arm, randomized, placebo-controlled, double-blind trial. Participants will be randomly allocated to receive either (a) Silexan 160 mg or (b) an identical appearing inert placebo, daily for 12 weeks in addition to their usual prescribed medications.
| Arm | Type | Receives |
|---|---|---|
| Silexan 160 mg | Experimental | Drug: SilexanParticipants in the Silexan arm will take Silexan 160 mg daily in the morning for 12 weeks in addition to their usual prescribed psychoactive medications. Participants will be followed up at 2, 4, 6, 8 and 12 weeks of the intervention period, as well as at 4 weeks post-treatment (off-treatment follow-up period). |
| Placebo | Placebo comparator | Other: PlaceboParticipants in this arm will take two placebo capsules daily in the morning for 12 weeks in addition to their usual medications. Participants will be followed up at 2, 4, 6, 8 and 12 weeks of the intervention period, as well as at 4 weeks post-treatment (off-treatment follow-up period). |
Who may qualify
- Ages
- 18 years and older
- Sex
- All
- Healthy volunteers
- Not accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (4 listed)
- Aged 18 years or over.
- Fluent in English.
- Meet DSM-5 criteria for PTSD, irrespective of occupation (e.g. first responder, police officer, ex-military or civilian), determined using the Mini International Neuropsychiatric Interview 7.0.2.
- Have a score on the PTSD Checklist for DSM-5 (PCL-5) equal to or over 33.
Key exclusion criteria (14 listed)
- Are currently serving in the Australian Defence Force
- Lifetime history of a psychotic or bipolar disorder, or dissociative identity disorder.
- Moderate or severe alcohol or other substance use disorder within 3 months of screening.
- Active suicidal or homicidal ideation.
- Borderline Personality Disorder (BPD).
Eligibility is decided by the study team after screening; this overview does not establish that a patient qualifies. Full inclusion and exclusion criteria.
Interventions
| Intervention | Type | Arms |
|---|---|---|
| SilexanParticipants in the Silexan arm will take two over-encapsulated capsules, each containing 80 mg Silexan, daily orally in the morning in addition to their usual medications. No modifications of allocated interventions will be made for any trial participants; if appropriate (i.e following the emergence of adverse events) participants will be withdrawn from the intervention. | Drug | Silexan 160 mg |
| PlaceboParticipants in the placebo arm will take two capsules containing an inert placebo daily orally in the morning in addition to their usual medications. The placebo capsules will contain a sub-therapeutic amount of lavender oil to mimic the odor of the experimental drug (Silexan). | Other | Placebo |
Primary outcome
Clinician-Administered PTSD Scale for DSM-5 (CAPS-5)
Time frame: At baseline and at week 12 of the study period
The Primary Outcome Measure will be the between-group difference in the change from baseline to week 12 in the total symptom severity score on the CAPS-5. The CAPS-5 has good internal consistency, inter-rater reliability, test-retest reliability and convergent validity in measuring PTSD symptom severity, and is regarded as the gold-standard for measuring PTSD symptoms in research settings. The CAPS-5 will be used to query the presence of PTSD symptoms across the two weeks prior to each CAPS-5 assessment. We will also compare between-group differences in remission rates of PTSD, as determined by the CAPS-5.
19 secondary outcomes
Hamilton Anxiety Rating Scale (HAM-A)
Time frame: At baseline, at week 12 and at week 16 of the study period
Generalized Anxiety Disorder-7 (GAD-7)
Time frame: At baseline, at week 12 and at week 16 of the study period
Generalized Anxiety Disorder-7 (GAD-7)
Time frame: At baseline, week 4, week 8 and week 12 of the study period
Beck Depression Inventory-II (BDI-II)
Time frame: At baseline, at week 12 and at week 16 of the study period
Patient Health Questionnaire-9 (PHQ-9)
Time frame: At baseline, at week 12 and at week 16 of the study period
Patient Health Questionnaire-9 (PHQ-9)
Time frame: At baseline, week 4, week 8 and week 12 of the study period
Patient Health Questionnaire-15 (PHQ-15)
Time frame: At baseline, at week 12 and at week 16 of the study period
Patient Health Questionnaire-15 (PHQ-15)
Time frame: At baseline, week 4, week 8 and week 12 of the study period
Pittsburgh Sleep Quality Index, with Addendum for PTSD (PSQI & PSQI-A)
Time frame: At baseline, at week 12 and at week 16 of the study period
Pittsburgh Sleep Quality Index, with Addendum for PTSD (PSQI & PSQI-A)
Time frame: At baseline, week 4, week 8 and week 12 of the study period
Alcohol Use Disorders Identification Test (AUDIT)
Time frame: At baseline, at week 12 and at week 16 of the study period
Alcohol Use Disorders Identification Test (AUDIT)
Time frame: At baseline, week 4, week 8 and week 12 of the study period
World Health Organization (WHO) Disability Assessment Schedule (WHODAS 2.0)
Time frame: At baseline, at week 12 and at week 16 of the study period
General Well Being Schedule (GWBS)
Time frame: At baseline, at week 12 and at week 16 of the study period
Assessment of Quality of Life-6D (AQoL-6D)
Time frame: At baseline, at week 12 and at week 16 of the study period
PTSD Checklist for DSM-5 (PCL-5)
Time frame: At intake, at week 12 and at week 16 of the study period
PTSD Checklist for DSM-5 (PCL-5)
Time frame: At intake, week 2, week 4, week 6, week 8 and week 12 of the study period
Patient Global Impression of Change Scale (PGIC)
Time frame: Week 2, week 4, week 6, week 8 and week 12 of the study period
Actigraphy watches
Time frame: Continously from baseline until week 16 of the study period
Results and safety
This study is still under way. Results are not available in the source record yet.
Research links
- Official record on ClinicalTrials.govLast updated by the sponsor 18 Dec 2025.
- Derived from this study: PubMed 41736003Roebuck G, Parkin GM, O'Donnell M, Khanna R, Forbes D, Lau W, Serpell S, Al-Azzawi H, Santamaria E, Mohebbi M, Iyer R, Dean O, Kanaan RA, Hopwood M, Green JE, Berk M. The Silexan in the Treatment Of Posttraumatic stress disorder (STOP) trial: protocol for a 12-week randomised controlled trial of adjunctive Silexan for PTSD. BMC Complement Med Ther. 2026 Feb 24;26(1):122. doi: 10.1186/s12906-026-05312-7.
- Individual participant dataSharing planned: Yes. The National Institute of Mental Health Data Archive (NDA) will be used as an online data-sharing repository. De-identified participant data will be linked in the shared data repository using an assigned NDA Global Unique Identifier (GUID). The GUID itself is not personally identifiable information or protected health information.
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Referral and contact
AzTrials does not enrol participants or take referrals. Contact the study team or a site listed below; they decide who can take part.
Michael Berk, PhD principal investigator
Deakin University
4 sites in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A Phase 3 study testing Silexan in people with Post Traumatic Stress Disorder, run by Deakin University at 4 sites in Australia.
The full registered description is in the About this study section and the official record.
Who may be eligible to take part?
The sponsor lists 4 inclusion and 14 exclusion criteria. Eligibility is decided by the study team after screening, so read the full criteria and contact a listed site.
Is this clinical trial currently recruiting?
The record says: looking for participants now, as of the sponsor's last update on 18 Dec 2025. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 4 sites in Australia. Whether a site is taking part right now should be confirmed with that site. See every site.
What are the possible benefits and risks?
They depend on the study and the treatment, and no study can promise a benefit. Some participants in this study may receive a placebo. The study team explains the known risks during informed consent, before anyone joins; the record itself does not list them.
What does this phase mean?
Phase 3 studies compare the treatment with the current standard treatment or a placebo in a large group, to confirm how well it works and watch for side effects.
Not every study follows the same path, and some studies (observational studies, device studies) have no phase.
Are results available for this study?
This study is still under way. Results are not available in the source record yet.
How can a doctor refer a patient or contact the research team?
Contact Greg Roebuck, MD (+61 3 9035 4749, greg.roebuck@unimelb.edu.au), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Clinician-Administered PTSD Scale for DSM-5 (CAPS-5) (time frame: At baseline and at week 12 of the study period). It is what the study was designed to measure, not a finding.
Where can I read the original study information?
On the ClinicalTrials.gov record for NCT06412757, which also lists 1 linked publication.
Does a listing mean the treatment is approved or proven to work?
No. A listing means the study is registered. It does not show that the treatment is safe, works, or is approved by a regulator.
How often is this information updated?
AzTrials copies changed records from ClinicalTrials.gov every night and reloads the whole registry every week. The sponsor last updated this record on 18 Dec 2025.