Depression - Major Depressive DisorderFLEXNCT07424781
Fluoxetine on Emotional Experience (FLEX) Study
A study testing Fluoxetine in people with Depression - Major Depressive Disorder and Irritability, run by University of Oxford at 1 site in United Kingdom.
Trial summary
The goal of this clinical medicine study is to investigate how does antidepressant fluoxetine modulate anger processing in healthy young people . The main questions it aims is to answer are: 1. How does fluoxetine affect responses to anger-related stimuli such as words, faces, and autobiographical recall? 2. Read more about this study
- Who is it for?
- Ages 18 to 24 yearsHealthy volunteers can take part
- Conditions the study is for
- Depression - Major Depressive Disorder, Irritability, Depression
- What is being tested?
- Fluoxetine
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 80 participants
- Where
- 1 siteUnited Kingdom
- Study dates
- 1 Oct 2025to 31 Dec 2026
- Phase
- Interventional
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 to 24 years
- All sexes
- Healthy volunteers accepted
- Adult
Who may be able to join
- Be aged 18-24 years (inclusive)
- Be resident in the UK for the duration of the study
- Have normal or corrected to normal vision
- Participant is willing and able to give informed consent for participation in the research
- Sufficiently fluent English to understand and complete the study
Who cannot join
- The participant may not enter the study if ANY of the following apply:
- Psychiatric History:
- Current or past diagnosis of any psychiatric disorder, as determined by the Structured Clinical Interview for the DSM-5 (SCID-5) and self-report. This includes, but is not limited to, depression, anxiety disorders, alcohol or drug dependency, personality disorders, suicidal ideation, and other psychiatric conditions;
- First degree relative with a diagnosis of mania;
- Lifestyle:
- Heavy smoker or vaper (> 10 cigarettes per day, or >2 mL e-liquid, or >15mg/day from a nicotine patch);
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- Heavy use of caffeine (drink > 4 of 250ml cups/cans of coffee or energy drinks per day);
- Heavy drinker (drink >14 standard alcoholic drinks per week);
- Current or recent use (in the last 3 months) of any psychoactive substance according to self-report and a urine drug test screening for recent use of 10 common recreational substances;
- Physical Health:
- Severely underweight or overweight in a manner that renders them unsuitable for the study in the opinion of the study medical advisor;
- Known contraindication to fluoxetine, such as hypersensitivity to fluoxetine or any component in its formulation;
- Pregnancy, as determined by a urine pregnancy test or plans to become pregnant within the next 3 months;
- Breastfeeding;
- Not able to consume gelatine;
- Medical History:
- Past or ongoing health issue which, in the opinion of the study medical advisor, may interfere with the safety of the participant or the scientific integrity of the study, including but not limited to: seizures or epilepsy, heart rhythm problem, renal disease, hepatic disease, glaucoma, diabetes, bleeding disorders or clotting conditions (e.g., haemophilia, thrombocytopenia);
- Diagnosis of a significant neurological condition (e.g., epilepsy, multiple sclerosis, traumatic brain injury).
- Diagnosis of a neurodevelopmental condition, such as autism spectrum disorder (ASD) or attention-deficit/hyperactivity disorder (ADHD);
- Current or recent use of medication that might interfere or interact with the effects of fluoxetine, in the opinion of the study medical advisor, including but not limited to: monoamine oxidase inhibitors (MAOIs), medications affecting serotonin levels (e.g., tramadol, triptans, St. John's Wort), anticoagulants or blood thinners (e.g., warfarin), anti-inflammatory medications (e.g., aspirin, ibuprofen), or medications known to affect heart rhythm;
- Prior Study Participation:
- Participation in any other psychological or medical experiment involving taking any kind of drug/medication/vaccine, within the last 3 months;
- Participation in any other study involving the current or similar tasks, within the last 6 months;
- Others
- •Any other significant finding which may arise during the screening process and which, in the opinion of the Principal Investigator/medical advisor, may influence the scientific integrity of the study, or the participant's ability to participate in the study.
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
United Kingdom1 site, 1 recruiting
- Recruiting
Department of Psychiatry, University of Oxford
Oxford, Oxfordshire, OX3 7JX
Ye Wo, MSc, 07564300004, ye.wo@psych.ox.ac.uk
About this study
Official title: The Effect of Fluoxetine Treatment on Anger Processing in Healthy Young People
The goal of this clinical medicine study is to investigate how does antidepressant fluoxetine modulate anger processing in healthy young people . The main questions it aims is to answer are:
- How does fluoxetine affect responses to anger-related stimuli such as words, faces, and autobiographical recall?
- How does fluoxetine influence responses during frustration induction in frustrative non-reward and threat paradigms?
- Does the effect manifest in physiological markers, including heart rate variability and facial expressions?
Read more
Researchers will compare fluoxetine to a placebo to see if drug fluoxetine affects anger processing.
Participants will:
Take 20mg fluoxetine or a placebo every day for 7 days. Visit the university site for questionnaire and tasks assessments. Heart rate variability and facial expressions will be recorded in some of the tasks.
- Being tested
- Fluoxetine, Placebo
- Keywords
- depression, young people, fluoxetine, irritability, anger
- Medical subject headings
- Depression
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
FluoxetineDrug
Participants will receive 20mg of fluoxetine daily for 7 days. Tablets encapsulated to aid blinding.
PlaceboDrug
Participants will receive one dose placebo (sucrose) daily for 7 days. Tablets encapsulated to aid blinding.
| Study group | Role | What they receive |
|---|---|---|
| fluoxetine | Active comparator | Participants will be taking 20mg fluoxetine daily. Receives: Drug: Fluoxetine |
| placebo | Placebo comparator | Participants will be taking one placebo capsule daily. Receives: Drug: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
Behavioral Measure: Facial Expression Recognition Task (FERT)
Recognition of angry faces in the Facial Expression Recognition Task
Measured: On the last day of the 7-day treatment
Secondary outcomes (8)
Behavioural Measure: The Affordances Task
Performance on an affordances task in which participants have to decide to fight or escape under threatening situations with different environmental affordance conditions.
Measured: On the last day of the 7-day treatment
Behavioural Measure: Emotional Categorization Task (ECAT)
Performance on recognising and memorising anger related words in the Emotional Categorization Task (ECAT)
Measured: On the last day of the 7-day treatment.
Performance on Carnival Task
Performance on an anger induction task in which the study's rigged design creates frustrating non-reward responses.
Measured: On the last day of the 7-day treatment.
Subjective Measure: Rest Task
Participants' rating of anger-related emotions during a resting task.
Measured: On the last day of the 7-day treatment.
Subjective Measure: Anger Memory Recall Task
Participants' ratings of anger-related emotions and bodily sensations during a task that involves guided imagery of a past personal experience.
Measured: On the last day of the 7-day treatment.
Physiological Measure: Heart Rate Variability
Heart rate variability measures across a battery of anger-induction tasks.
Measured: On the last day of the 7-day treatment.
Physiological Measure: Facial Expression
Video recordings that identify facial expressions across a battery of anger-induction tasks.
Measured: On the last day of the 7-day treatment.
Behavioural measure: Emotional Recognition Memory Task (EMEM)
Description: Performance on recognising and memorising anger related words in the Emotional Recognition Memory Task (EMEM).
Measured: On the last day of the 7-day treatment.
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted20 Feb 2026
- Study start1 Oct 2025
- Primary completion31 Dec 2026 (estimated)
- Study completion31 Dec 2026 (estimated)
Resources
- Official record on ClinicalTrials.govThe registry entry this page is built from, with its full change history.
- Other trials for Depression - Major Depressive DisorderStudies of the same condition, open and under way.
- More trials run by University of OxfordThe sponsor's other registered studies.
- 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 N/A
- Primary purpose
- Basic science
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Model description
- Participants will be assigned to receive either fluoxetine or placebo. Fluoxetine is not being administered for treatment purposes, the purpose is to understand the mechanisms underpinning its effects.
- Masking
- Triple blind
- Who is masked
- Participant, Investigator, Outcomes assessor
- Enrolment
- 80 participants (estimated)
Sponsor and investigators
- Lead sponsor
- University of Oxford
- Sponsor type
- University, hospital or other
- Collaborators
- Wellcome Trust, National Institute for Health Research, United Kingdom
- Responsible party
- Principal investigator, Catherine Harmer, University of Oxford
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07424781
- Sponsor's protocol ID
- MS IDREC 1017147
- Acronym
- FLEX
- Status last verified
- Sep 2025
- First submitted
- 3 Dec 2025
- Last updated
- 20 Feb 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: Data which has been fully de-identified and relevant supporting materials (e.g., study protocol, data dictionary, and analysis documentation) may be shared with other academic organisations in the future, including those outside of the UK and the EU. Participants will be informed of this and specific consent to this is obtained within the Informed Consent Form.