The Effect of 5-hydroxytryptophan on ADHD Traits and Eye Movements

August 18, 2026 updated by: Eleanor Jackson, University of Sheffield

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.

Study Overview

Status

Status

Indicates the current recruitment status or the expanded access status.
Recruiting

Conditions

Conditions

The disease, disorder, syndrome, illness, or injury that is being studied. On ClinicalTrials.gov, conditions may also include other health-related issues, such as lifespan, quality of life, and health risks.

Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.

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 Type

Study Type

Describes the nature of a clinical study. Study types include interventional studies (also called clinical trials), observational studies (including patient registries), and expanded access.
Interventional

Enrollment (Estimated)

Enrollment

The number of participants in a clinical study. The "anticipated" enrollment is the target number of participants that the researchers need for the study.
150

Phase

Phase

The stage of a clinical trial studying a drug or biological product, based on definitions developed by the U.S. Food and Drug Administration (FDA). The phase is based on the study's objective, the number of participants, and other characteristics. There are five phases: Early Phase 1 (formerly listed as Phase 0), Phase 1, Phase 2, Phase 3, and Phase 4. Not Applicable is used to describe trials without FDA-defined phases, including trials of devices or behavioral interventions.
  • Not Applicable

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Contact

Study Contact

The name and contact information for the person who can answer enrollment questions for a clinical study. Each location where the study is being conducted may also have a specific contact, who may be better able to answer those questions.

Study Contact Backup

Study Locations

  • United Kingdom
    • South Yorkshire
      • Sheffield, South Yorkshire, United Kingdom, S10 2TN

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Eligibility Criteria

The key requirements that people who want to participate in a clinical study must meet or the characteristics they must have. Eligibility criteria consist of both inclusion criteria (which are required for a person to participate in the study) and exclusion criteria (which prevent a person from participating). Types of eligibility criteria include whether a study accepts healthy volunteers, has age or age group requirements, or is limited by sex.

Ages Eligible for Study

  • Adult
  • Older Adult

Accepts Healthy Volunteers

Yes

Description

Inclusion Criteria:

  • 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)

Exclusion Criteria:

  • 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

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

  • Primary Purpose: Treatment
  • Allocation: Randomized
  • Interventional Model: Parallel Assignment
  • Masking: None (Open Label)

Arms and Interventions

Participant Group / Arm

Participant Group / Arm

A group or subgroup of participants in a clinical trial that receives a specific intervention/treatment, or no intervention, according to the trial's protocol.
Intervention / Treatment

Intervention / Treatment

A process or action that is the focus of a clinical study. Interventions include drugs, medical devices, procedures, vaccines, and other products that are either investigational or already available. Interventions can also include noninvasive approaches, such as education or modifying diet and exercise.
Experimental: High ADHD traits - 200mg 5-HTP
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.
Dietary supplement: 5-hydroxytryptophan (food supplement) 200mg
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).
Other Names:
  • 5-HTP
Experimental: High ADHD traits - 300mg 5-HTP
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.
Dietary supplement: 5-hydroxytryptophan (food supplement) 300mg
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).
Other Names:
  • 5-HTP
Placebo Comparator: High ADHD traits - Placebo
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.
Other: Placebo
Unmedicated lactose-sucrose tablets provided by Ainsworth's homoeopathic remedies
Active Comparator: Low ADHD traits - 200mg 5-HTP
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.
Dietary supplement: 5-hydroxytryptophan (food supplement) 200mg
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).
Other Names:
  • 5-HTP
Active Comparator: Low ADHD traits - 300mg 5-HTP
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.
Dietary supplement: 5-hydroxytryptophan (food supplement) 300mg
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).
Other Names:
  • 5-HTP
Placebo Comparator: Low ADHD traits - placebo
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.
Other: Placebo
Unmedicated lactose-sucrose tablets provided by Ainsworth's homoeopathic remedies

What is the study measuring?

Primary Outcome Measures

Primary Outcome Measures

In a clinical study's protocol, the planned outcome measure that is the most important for evaluating the effect of an intervention/treatment. Most clinical studies have one primary outcome measure, but some have more than one.
Outcome Measure
Measure Description
Time Frame
Change in distractibility - microsaccades
Time Frame: pre and 90 minutes post administration
Frequency of microsaccades in a simple fixation task
pre and 90 minutes post administration
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.
pre and 90 minutes post administration
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.
pre and 90 minute post administration

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Sponsor

Sponsor

The organization or person who initiates the study and who has authority and control over the study.
University of Sheffield

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

General Publications

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start (Actual)

Study Start

The actual date on which the first participant was enrolled in a clinical study. The "anticipated" study start date is the date that the researchers think will be the study start date.
November 25, 2025

Primary Completion (Estimated)

Primary Completion

The date on which the last participant in a clinical study was examined or received an intervention to collect final data for the primary outcome measure. Whether the clinical study ended according to the protocol or was terminated does not affect this date. For clinical studies with more than one primary outcome measure with different completion dates, this term refers to the date on which data collection is completed for all the primary outcome measures. The "anticipated" primary completion date is the date that the researchers think will be the primary completion date for the study.
February 1, 2027

Study Completion (Estimated)

Study Completion

The date on which the last participant in a clinical study was examined or received an intervention/treatment to collect final data for the primary outcome measures, secondary outcome measures, and adverse events (that is, the last participant's last visit). The "anticipated" study completion date is the date that the researchers think will be the study completion date.
June 1, 2027

Study Registration Dates

First Submitted

First Submitted

The date on which the study sponsor or investigator first submitted a study record to ClinicalTrials.gov. There is typically a delay of a few days between the first submitted date and the record's availability on ClinicalTrials.gov (the first posted date).
August 12, 2026

First Submitted That Met QC Criteria

First Submitted That Met QC Criteria

The date on which the study sponsor or investigator first submits a study record that is consistent with National Library of Medicine (NLM) quality control (QC) review criteria. The sponsor or investigator may need to revise and submit a study record one or more times before NLM's QC review criteria are met. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
August 18, 2026

First Posted (Actual)

First Posted

The date on which the study record was first available on ClinicalTrials.gov after National Library of Medicine (NLM) quality control (QC) review has concluded. There is typically a delay of a few days between the date the study sponsor or investigator submitted the study record and the first posted date.
August 20, 2026

Study Record Updates

Last Update Posted (Actual)

Last Update Posted

The most recent date on which changes to a study record were made available on ClinicalTrials.gov. There may be a delay between when the changes were submitted to ClinicalTrials.gov by the study's sponsor or investigator (the last update submitted date) and the last update posted date.
August 20, 2026

Last Update Submitted That Met QC Criteria

Last Update Submitted That Met QC Criteria

The most recent date on which the study sponsor or investigator submitted changes to a study record that are consistent with National Library of Medicine (NLM) quality control (QC) review criteria. It is the responsibility of the sponsor or investigator to ensure that the study record is consistent with the NLM QC review criteria.
August 18, 2026

Last Verified

Last Verified

The most recent date on which the study sponsor or investigator confirmed the information about a clinical study on ClinicalTrials.gov as accurate and current. If a study with a recruitment status of recruiting; not yet recruiting; or active, not recruiting has not been confirmed within the past 2 years, the study's recruitment status is shown as unknown.
August 1, 2026

More Information

Terms related to this study

Keywords

Additional Relevant MeSH Terms

Other Study ID Numbers

Other Study ID Numbers

Identifiers or ID numbers other than the NCT number that are assigned to a clinical study by the study's sponsor, funders, or others. These numbers may include unique identifiers from other trial registries and National Institutes of Health grant numbers.
  • 070759
  • 10.17605/OSF.IO/7GWMC (Other Identifier: OSF)

Plan for Individual participant data (IPD)

Plan to Share Individual Participant Data (IPD)?

YES

IPD Plan Description

IPD regarding group allocation, ASRS scores, and measures on microsaccades and visual search tasks will be shared following completion of the study.

IPD Sharing Supporting Information Type

  • STUDY_PROTOCOL
  • SAP

Drug and device information, study documents

Studies a U.S. FDA-regulated drug product

No

Studies a U.S. FDA-regulated device product

No

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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