Attention Deficit and Hyperactivity Disorder (ADHD)NCT07777328
The Effect of 5-hydroxytryptophan on ADHD Traits and Eye Movements
A study testing 5-hydroxytryptophan (food supplement) 200mg and 5-hydroxytryptophan (food supplement) 300mg in people with Attention Deficit and Hyperactivity Disorder (ADHD) and Attention Deficit Hyperactivity Disorder in Adults, run by University of Sheffield at 1 site in United Kingdom.
Trial summary
The aim of this project is to look at the impact of 5-Hydroxytryptophan (5-HTP) on distractibility. 5-HTP is the precursor to the neurotransmitter serotonin and is a chemical that the body produces naturally. There is evidence that distractibility is associated with a decreased level of serotonin. Read more about this study
- Who is it for?
- Ages 18 to 65 yearsHealthy volunteers can take part
- Conditions the study is for
- Attention Deficit and Hyperactivity Disorder (ADHD), Attention Deficit Hyperactivity Disorder in Adults, Attention Deficits
- What is being tested?
- 5-hydroxytryptophan (food supplement) 200mg and 5-hydroxytryptophan (food supplement) 300mg
- Type of treatment
- Pill or oral medicine
- Could I receive a placebo?
- Yes, some participants may receive a placebo
- How many people
- 150 participants
- Where
- 1 siteUnited Kingdom
- Study dates
- 25 Nov 2025to Jun 2027
- Phase
- Interventional
- 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 to 65 years
- All sexes
- Healthy volunteers accepted
- Adult, Older adult
Who may be able to join
- 18-65 years of age
- Normal or corrected to normal vision with contact lenses.
- Score of <9 or >14 on the ASRS v5 (assessed in pre screen questionnaire)
Who cannot join
- Current use of psychostimulant medication or medication for the treatment of ADHD
- Current use of medications known to impact the serotonergic system (e.g., SSRIs).
- Smoking or vaping
- Pregnancy
- Breast feeding
- Lactose intolerance
- Veganism
- Dyslexia
Trial locations and contacts
1 site in 1 country. Contact the study team or a site near you to ask about taking part.
Paul G Overton, Professor contact
United Kingdom1 site, 1 recruiting
- Recruiting
University of Sheffield
Sheffield, South Yorkshire, S10 2TN
Eleanor Jackson, +447908873415, efjackson1@sheffield.ac.uk
About this study
Official title: The Effect of 5-hydroxytryptophan on Microsaccades and Distractibility in Individual With High Levels of ADHD Traits: a Randomised, Double-blind Trial
The aim of this project is to look at the impact of 5-Hydroxytryptophan (5-HTP) on distractibility. 5-HTP is the precursor to the neurotransmitter serotonin and is a chemical that the body produces naturally. There is evidence that distractibility is associated with a decreased level of serotonin. This research aims to see if giving people 5-HTP will alter their distractibility, which will form part of an initial assessment as to whether 5-HTP could be used to support people with attention problems. The study involves completing a short survey about mental health and behaviours, and if eligible, participation in an in-person study at the University of Sheffield. The in-person session involves completing some cognitive tasks to look at eye movement, taking 5-HTP or a sugar tablet with no active ingredients, and then completing the tasks again after a 90-minute wait.
Read the detailed description
The overarching aim of this project is to assess the efficacy and suitability of 5-hydroxytryptophan, a nutritional supplement and precursor to serotonin, as a potential therapeutic for ADHD traits. 5-hydroxytryptophan is a metabolic product produced in the body following consumption of foods with high levels of the amino acid tryptophan, found in soy products, egg whites, and other high-protein foods. Both tryptophan and 5-hydroxytryptophan are metabolic precursors to serotonin, a neurotransmitter that is essential for the regulation of sleep, emotional state, aggression, and, most relevantly, the regulation of attention. Serotonin levels have been shown to be significantly reduced in individuals with ADHD, and some theories suggest that this is linked to reduced serotonin synthesis; of particular interest is the step where tryptophan is converted to 5-hydroxytryptophan, both the rate-limiting step of serotonin synthesis and a possible genetic locus of change in ADHD. 5-hydroxytryptophan can be readily obtained from health shops as a supplement, derived from the seeds of the edible plant Griffonia Simplicifolia, which has been long used in traditional medicine, and its ability to be absorbed easily from the intestinal tract and skip the rate-limiting step of synthesis makes it an attractive possible therapeutic. Pre-clinical work where 5-hydroxytryptophan was administered to Rhesus Macaques found that the supplement increased attention in animals with a low baseline level of attention, highlighting a possible benefit to supplementation.
Although theoretically promising, our previous empirical study failed to find any effect of 5-hydroxytryptophan supplementation on individuals with high or low levels of ADHD-like traits. The study had several limitations, a significant one being that tasks that were meant to assess distractibility did not show a distractor effect, and did not provide discrimination between high and low ADHD trait groups. As such, we aim to attempt to re-assess the impact of 5-hydroxytryptophan with tasks that are better established as being ADHD-sensitive, particularly those of microsaccades and ocular motor behaviour, alongside a distractor task established in a previous pilot. Our primary study design also only considered one dose of 5-hydroxytryptophan, whereas in this iteration, we will use two different doses of 5-hydroxytryptophan to better establish a dose-response effect. Finally, given the heterogeneity of ADHD-traits and comorbidity with other neurodevelopmental and psychiatric conditions, we intend to better characterise the affective state of the cohort in order to better control for confounds and co-morbidity in the final data set.
The proposed study will be conducted in two parts:
A pre-screen survey to determine participant eligibility:
AIM = to assess the eligibility and ADHD traits of potential participants.
In-person participation in a randomised, double-blind trial at the University of Sheffield, where participants will ingest either intervention or placebo and complete cognitive tasks pre- and post-administration.
AIM = to determine the impact of 5-hydroxytryptophan supplementation on cognitive and oculomotor behaviour of individuals with high and low levels of ADHD traits.
- Conditions
- Attention Deficit and Hyperactivity Disorder (ADHD), Attention Deficit Hyperactivity Disorder in Adults, Attention Deficits
- Being tested
- 5-hydroxytryptophan (food supplement) 200mg, 5-hydroxytryptophan (food supplement) 300mg, Placebo
- Keywords
- 5-Hydroxytryptophan, Serotonin, ADHD, microsaccades, eye tracking, attention
- Medical subject headings
- Attention Deficit Disorder with Hyperactivity
What participants receive
What participants receive. In a randomised study each person is assigned to one group by chance.
5-hydroxytryptophan (food supplement) 200mgDietary supplement
Also called 5-HTP
200mg 5-HTP delivered in two tablets. Tablets obtained from Nature's Best supplements. Each tablet contains 3982mg of Griffonia seed extract, providing 100mg of 5-HTP. The tablets consist of calcium carbonate, griffonia seed extract, Anti-caking Agents (Silicon Dioxide, Stearic Acid, \& Magnesium Stearate) and Tablet Coating (Hydroxypropyl Methylcellulose, Glycerol).
5-hydroxytryptophan (food supplement) 300mgDietary supplement
Also called 5-HTP
300mg 5-HTP delivered in three tablets. Tablets obtained from Nature's Best supplements. Each tablet contains 3982mg of Griffonia seed extract, providing 100mg of 5-HTP. The tablets consist of calcium carbonate, griffonia seed extract, Anti-caking Agents (Silicon Dioxide, Stearic Acid, \& Magnesium Stearate) and Tablet Coating (Hydroxypropyl Methylcellulose, Glycerol).
PlaceboOther
Unmedicated lactose-sucrose tablets provided by Ainsworth's homoeopathic remedies
| Study group | Role | What they receive |
|---|---|---|
| High ADHD traits - 200mg 5-HTP | Experimental | Participants who have reported high levels of ADHD traits, and have been randomly allocated to the group receiving 200 mg 5-HTP, administered orally in tablet form. Receives: Dietary Supplement: 5-hydroxytryptophan (food supplement) 200mg |
| High ADHD traits - 300mg 5-HTP | Experimental | Participants who have reported high levels of ADHD traits, and have been randomly allocated to the group receiving 300 mg 5-HTP, administered orally in tablet form. Receives: Dietary Supplement: 5-hydroxytryptophan (food supplement) 300mg |
| High ADHD traits - Placebo | Placebo comparator | Participants who have reported high levels of ADHD traits, and have been randomly allocated to the group receiving placebo. Placebo consists of 2 sucrose-lactose tablets, administered orally. Receives: Other: Placebo |
| Low ADHD traits - 200mg 5-HTP | Active comparator | Participants who have reported low levels of ADHD traits, and have been randomly allocated to the group receiving 200 mg 5-HTP, administered orally in tablet form. Receives: Dietary Supplement: 5-hydroxytryptophan (food supplement) 200mg |
| Low ADHD traits - 300mg 5-HTP | Active comparator | Participants who have reported low levels of ADHD traits, and have been randomly allocated to the group receiving 300 mg 5-HTP, administered orally in tablet form. Receives: Dietary Supplement: 5-hydroxytryptophan (food supplement) 300mg |
| Low ADHD traits - placebo | Placebo comparator | Participants who have reported low levels of ADHD traits, and have been randomly allocated to the group receiving placebo. Placebo consists of 2 sucrose-lactose tablets, administered orally. Receives: Other: Placebo |
What is being measured
The primary outcome is the main question the study is designed to answer.
Change in distractibility - microsaccades
Frequency of microsaccades in a simple fixation task
Measured: pre and 90 minutes post administration
Change in distractibility - reaction time
Measurement of reaction time on a visual search task with varying auditory stimuli.
Measured: pre and 90 minutes post administration
Change in distractibility- fixations
Number of fixations on distractor letters in a visual search task with varying auditory stimuli.
Measured: pre and 90 minute post administration
Timeline
From the start of the study to its completion; the mark is today. Estimated dates are the sponsor’s plan.
- First posted20 Aug 2026
- Study start25 Nov 2025
- Primary completionFeb 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 (9)Papers the sponsor has linked to this study.
- Other trials for Attention Deficit and Hyperactivity Disorder (ADHD)Studies 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 N/A
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Enrolment
- 150 participants (estimated)
Sponsor and investigators
- Lead sponsor
- University of Sheffield
- Sponsor type
- University, hospital or other
- Responsible party
- Principal investigator, Eleanor Jackson, University of Sheffield
IDs, dates and publications
- ClinicalTrials.gov ID
- NCT07777328
- Sponsor's protocol ID
- 070759
- Other IDs
- 10.17605/OSF.IO/7GWMC
- Status last verified
- Aug 2026
- First submitted
- 12 Aug 2026
- Last updated
- 20 Aug 2026
- Results posted
- No
- Data monitoring committee
- No
- FDA-regulated drug
- No
- FDA-regulated device
- No
- Individual data sharing
- Yes: IPD regarding group allocation, ASRS scores, and measures on microsaccades and visual search tasks will be shared following completion of the study.
Publications
Weinberg-Wolf H, Fagan NA, Anderson GM, Tringides M, Dal Monte O, Chang SWC. The effects of 5-hydroxytryptophan on attention and central serotonin neurochemistry in the rhesus macaque. Neuropsychopharmacology. 2018 Jun;43(7):1589-1598. doi: 10.1038/s41386-017-0003-7. Epub 2018 Jan 30.
PubMed 29463909Vigliante I, Mannino G, Maffei ME. Chemical Characterization and DNA Fingerprinting of Griffonia simplicifolia Baill. Molecules. 2019 Mar 15;24(6):1032. doi: 10.3390/molecules24061032.
PubMed 30875930Panagiotidi M, Paul O, Tom S. Increased microsaccade rate in individuals with ADHD traits. J Eye Mov Res. 2017 Mar 4;10(1):10.16910/jemr.10.1.6. doi: 10.16910/jemr.10.1.6.
PubMed 33828642Turner EH, Loftis JM, Blackwell AD. Serotonin a la carte: supplementation with the serotonin precursor 5-hydroxytryptophan. Pharmacol Ther. 2006 Mar;109(3):325-38. doi: 10.1016/j.pharmthera.2005.06.004. Epub 2005 Jul 14.
PubMed 16023217Lovejoy LP, Krauzlis RJ. Inactivation of primate superior colliculus impairs covert selection of signals for perceptual judgments. Nat Neurosci. 2010 Feb;13(2):261-6. doi: 10.1038/nn.2470. Epub 2009 Dec 20.
PubMed 20023651Lindseth G, Helland B, Caspers J. The effects of dietary tryptophan on affective disorders. Arch Psychiatr Nurs. 2015 Apr;29(2):102-7. doi: 10.1016/j.apnu.2014.11.008. Epub 2014 Dec 9.
PubMed 25858202Jackson E, Riley T, Overton PG. The effect of 5-hydroxytryptophan, a serotonin precursor, on adults with high levels of Attention Deficit Hyperactivity Disorder traits: A randomised, controlled trial. PLoS One. 2026 May 20;21(5):e0349512. doi: 10.1371/journal.pone.0349512. eCollection 2026.
PubMed 42160304Jackson EF, Riley TB, Overton PG. Serotonin dysfunction in ADHD. J Neurodev Disord. 2025 Apr 22;17(1):20. doi: 10.1186/s11689-025-09610-y.
PubMed 40264019Birdsall TC. 5-Hydroxytryptophan: a clinically-effective serotonin precursor. Altern Med Rev. 1998 Aug;3(4):271-80.
PubMed 9727088
Study at a glance
From the registry record, last updated by the sponsor on 20 Aug 2026. Recruitment status is as the sponsor reported it: confirm with the study team.
- Official title
- The Effect of 5-hydroxytryptophan on Microsaccades and Distractibility in Individual With High Levels of ADHD Traits: a Randomised, Double-blind Trial
- ClinicalTrials.gov ID
- NCT07777328
- Acronym / sponsor ID
- 070759
- Conditions
- Attention Deficit and Hyperactivity Disorder (ADHD), Attention Deficit Hyperactivity Disorder in Adults, Attention Deficits
- Keywords
- 5-Hydroxytryptophan, Serotonin, ADHD, microsaccades, eye tracking, attention
- Study type
- Interventional
- Recruitment status
- Recruiting
- Enrolment
- 150 participants (estimated)
- Lead sponsor
- University of SheffieldUniversity, hospital or other
- Study start
- 25 Nov 2025 (actual)
- Primary completion
- Feb 2027 (estimated)
- Study completion
- Jun 2027 (estimated)
- First posted
- 20 Aug 2026 (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.
The aim of this project is to look at the impact of 5-Hydroxytryptophan (5-HTP) on distractibility. 5-HTP is the precursor to the neurotransmitter serotonin and is a chemical that the body produces naturally. There is evidence that distractibility is associated with a decreased level of serotonin. This research aims to see if giving people 5-HTP will alter their distractibility, which will form part of an initial assessment as to whether 5-HTP could be used to support people with attention problems. The study involves completing a short survey about mental health and behaviours, and if eligible, participation in an in-person study at the University of Sheffield. The in-person session involves completing some cognitive tasks to look at eye movement, taking 5-HTP or a sugar tablet with no active ingredients, and then completing the tasks again after a 90-minute wait.
Detailed description
The overarching aim of this project is to assess the efficacy and suitability of 5-hydroxytryptophan, a nutritional supplement and precursor to serotonin, as a potential therapeutic for ADHD traits. 5-hydroxytryptophan is a metabolic product produced in the body following consumption of foods with high levels of the amino acid tryptophan, found in soy products, egg whites, and other high-protein foods. Both tryptophan and 5-hydroxytryptophan are metabolic precursors to serotonin, a neurotransmitter that is essential for the regulation of sleep, emotional state, aggression, and, most relevantly, the regulation of attention. Serotonin levels have been shown to be significantly reduced in individuals with ADHD, and some theories suggest that this is linked to reduced serotonin synthesis; of particular interest is the step where tryptophan is converted to 5-hydroxytryptophan, both the rate-limiting step of serotonin synthesis and a possible genetic locus of change in ADHD. 5-hydroxytryptophan can be readily obtained from health shops as a supplement, derived from the seeds of the edible plant Griffonia Simplicifolia, which has been long used in traditional medicine, and its ability to be absorbed easily from the intestinal tract and skip the rate-limiting step of synthesis makes it an attractive possible therapeutic. Pre-clinical work where 5-hydroxytryptophan was administered to Rhesus Macaques found that the supplement increased attention in animals with a low baseline level of attention, highlighting a possible benefit to supplementation.
Although theoretically promising, our previous empirical study failed to find any effect of 5-hydroxytryptophan supplementation on individuals with high or low levels of ADHD-like traits. The study had several limitations, a significant one being that tasks that were meant to assess distractibility did not show a distractor effect, and did not provide discrimination between high and low ADHD trait groups. As such, we aim to attempt to re-assess the impact of 5-hydroxytryptophan with tasks that are better established as being ADHD-sensitive, particularly those of microsaccades and ocular motor behaviour, alongside a distractor task established in a previous pilot. Our primary study design also only considered one dose of 5-hydroxytryptophan, whereas in this iteration, we will use two different doses of 5-hydroxytryptophan to better establish a dose-response effect. Finally, given the heterogeneity of ADHD-traits and comorbidity with other neurodevelopmental and psychiatric conditions, we intend to better characterise the affective state of the cohort in order to better control for confounds and co-morbidity in the final data set.
The proposed study will be conducted in two parts:
A pre-screen survey to determine participant eligibility:
AIM = to assess the eligibility and ADHD traits of potential participants.
In-person participation in a randomised, double-blind trial at the University of Sheffield, where participants will ingest either intervention or placebo and complete cognitive tasks pre- and post-administration.
AIM = to determine the impact of 5-hydroxytryptophan supplementation on cognitive and oculomotor behaviour of individuals with high and low levels of ADHD traits.
Study design
- Primary purpose
- Treatment
- Allocation
- Randomised
- Intervention model
- Parallel groups
- Masking
- None (open label)
- Number of arms
- 6
| Arm | Type | Receives |
|---|---|---|
| High ADHD traits - 200mg 5-HTP | Experimental | Dietary Supplement: 5-hydroxytryptophan (food supplement) 200mgParticipants who have reported high levels of ADHD traits, and have been randomly allocated to the group receiving 200 mg 5-HTP, administered orally in tablet form. |
| High ADHD traits - 300mg 5-HTP | Experimental | Dietary Supplement: 5-hydroxytryptophan (food supplement) 300mgParticipants who have reported high levels of ADHD traits, and have been randomly allocated to the group receiving 300 mg 5-HTP, administered orally in tablet form. |
| High ADHD traits - Placebo | Placebo comparator | Other: PlaceboParticipants who have reported high levels of ADHD traits, and have been randomly allocated to the group receiving placebo. Placebo consists of 2 sucrose-lactose tablets, administered orally. |
| Low ADHD traits - 200mg 5-HTP | Active comparator | Dietary Supplement: 5-hydroxytryptophan (food supplement) 200mgParticipants who have reported low levels of ADHD traits, and have been randomly allocated to the group receiving 200 mg 5-HTP, administered orally in tablet form. |
| Low ADHD traits - 300mg 5-HTP | Active comparator | Dietary Supplement: 5-hydroxytryptophan (food supplement) 300mgParticipants who have reported low levels of ADHD traits, and have been randomly allocated to the group receiving 300 mg 5-HTP, administered orally in tablet form. |
| Low ADHD traits - placebo | Placebo comparator | Other: PlaceboParticipants who have reported low levels of ADHD traits, and have been randomly allocated to the group receiving placebo. Placebo consists of 2 sucrose-lactose tablets, administered orally. |
Who may qualify
- Ages
- 18 to 65 years
- Sex
- All
- Healthy volunteers
- Accepted
- Age groups
- Adult, Older adult
Key inclusion criteria (3 listed)
- 18-65 years of age
- Normal or corrected to normal vision with contact lenses.
- Score of <9 or >14 on the ASRS v5 (assessed in pre screen questionnaire)
Key exclusion criteria (8 listed)
- Current use of psychostimulant medication or medication for the treatment of ADHD
- Current use of medications known to impact the serotonergic system (e.g., SSRIs).
- Smoking or vaping
- Pregnancy
- Breast feeding
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 |
|---|---|---|
| 5-hydroxytryptophan (food supplement) 200mgAlso: 5-HTP200mg 5-HTP delivered in two tablets. Tablets obtained from Nature's Best supplements. Each tablet contains 3982mg of Griffonia seed extract, providing 100mg of 5-HTP. The tablets consist of calcium carbonate, griffonia seed extract, Anti-caking Agents (Silicon Dioxide, Stearic Acid, \& Magnesium Stearate) and Tablet Coating (Hydroxypropyl Methylcellulose, Glycerol). | Dietary supplement | High ADHD traits - 200mg 5-HTP, Low ADHD traits - 200mg 5-HTP |
| 5-hydroxytryptophan (food supplement) 300mgAlso: 5-HTP300mg 5-HTP delivered in three tablets. Tablets obtained from Nature's Best supplements. Each tablet contains 3982mg of Griffonia seed extract, providing 100mg of 5-HTP. The tablets consist of calcium carbonate, griffonia seed extract, Anti-caking Agents (Silicon Dioxide, Stearic Acid, \& Magnesium Stearate) and Tablet Coating (Hydroxypropyl Methylcellulose, Glycerol). | Dietary supplement | High ADHD traits - 300mg 5-HTP, Low ADHD traits - 300mg 5-HTP |
| PlaceboUnmedicated lactose-sucrose tablets provided by Ainsworth's homoeopathic remedies | Other | High ADHD traits - Placebo, Low ADHD traits - placebo |
Primary outcome
Change in distractibility - microsaccades
Time frame: pre and 90 minutes post administration
Frequency of microsaccades in a simple fixation task
Change in distractibility - reaction time
Time frame: pre and 90 minutes post administration
Measurement of reaction time on a visual search task with varying auditory stimuli.
Change in distractibility- fixations
Time frame: pre and 90 minute post administration
Number of fixations on distractor letters in a visual search task with varying auditory stimuli.
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 20 Aug 2026.
- Background: PubMed 29463909Weinberg-Wolf H, Fagan NA, Anderson GM, Tringides M, Dal Monte O, Chang SWC. The effects of 5-hydroxytryptophan on attention and central serotonin neurochemistry in the rhesus macaque. Neuropsychopharmacology. 2018 Jun;43(7):1589-1598. doi: 10.1038/s41386-017-0003-7. Epub 2018 Jan 30.
- Background: PubMed 30875930Vigliante I, Mannino G, Maffei ME. Chemical Characterization and DNA Fingerprinting of Griffonia simplicifolia Baill. Molecules. 2019 Mar 15;24(6):1032. doi: 10.3390/molecules24061032.
- Background: PubMed 33828642Panagiotidi M, Paul O, Tom S. Increased microsaccade rate in individuals with ADHD traits. J Eye Mov Res. 2017 Mar 4;10(1):10.16910/jemr.10.1.6. doi: 10.16910/jemr.10.1.6.
- Background: PubMed 16023217Turner EH, Loftis JM, Blackwell AD. Serotonin a la carte: supplementation with the serotonin precursor 5-hydroxytryptophan. Pharmacol Ther. 2006 Mar;109(3):325-38. doi: 10.1016/j.pharmthera.2005.06.004. Epub 2005 Jul 14.
- Background: PubMed 20023651Lovejoy LP, Krauzlis RJ. Inactivation of primate superior colliculus impairs covert selection of signals for perceptual judgments. Nat Neurosci. 2010 Feb;13(2):261-6. doi: 10.1038/nn.2470. Epub 2009 Dec 20.
- Background: PubMed 25858202Lindseth G, Helland B, Caspers J. The effects of dietary tryptophan on affective disorders. Arch Psychiatr Nurs. 2015 Apr;29(2):102-7. doi: 10.1016/j.apnu.2014.11.008. Epub 2014 Dec 9.
- Background: PubMed 42160304Jackson E, Riley T, Overton PG. The effect of 5-hydroxytryptophan, a serotonin precursor, on adults with high levels of Attention Deficit Hyperactivity Disorder traits: A randomised, controlled trial. PLoS One. 2026 May 20;21(5):e0349512. doi: 10.1371/journal.pone.0349512. eCollection 2026.
- Background: PubMed 40264019Jackson EF, Riley TB, Overton PG. Serotonin dysfunction in ADHD. J Neurodev Disord. 2025 Apr 22;17(1):20. doi: 10.1186/s11689-025-09610-y.
- Background: PubMed 9727088Birdsall TC. 5-Hydroxytryptophan: a clinically-effective serotonin precursor. Altern Med Rev. 1998 Aug;3(4):271-80.
- Individual participant dataSharing planned: Yes. IPD regarding group allocation, ASRS scores, and measures on microsaccades and visual search tasks will be shared following completion of the study.
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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.
Paul G Overton, Professor contact
1 site in 1 country: see every site and its status.
Questions about this trial
What is this clinical trial studying?
A study testing 5-hydroxytryptophan (food supplement) 200mg and 5-hydroxytryptophan (food supplement) 300mg in people with Attention Deficit and Hyperactivity Disorder (ADHD) and Attention Deficit Hyperactivity Disorder in Adults, run by University of Sheffield at 1 site in United Kingdom.
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 3 inclusion and 8 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 20 Aug 2026. Status can change between updates, so confirm with the study contact before making plans.
Where is the study taking place?
The record lists 1 site in United Kingdom. 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.
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 Eleanor F Jackson (+447908873415, efjackson1@sheffield.ac.uk), or a site near the patient. AzTrials does not enrol participants or take referrals.
What does the primary outcome measure?
Change in distractibility - microsaccades (time frame: pre and 90 minutes post administration). The study lists 3 primary outcomes in all. 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 NCT07777328, which also lists 9 linked publications.
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 20 Aug 2026.