Investigating the effects of acute tryptophan loading on attention and impulsivity in adults with and without Attention Deficit Hyperactivity Disorder (ADHD)

Investigating the effects of tryptophan modulation on attention and impulsivity in adults with and without Attention Deficit Hyperactivity Disorder: A double blind randomised controlled trial

Status

Active, not recruiting

Phases

Unknown

Study type

Interventional

Source

ISRCTN

Registry ID

ISRCTN15119603

Enrollment

144

Registered

2023-05-03

Start date

2020-07-01

Completion date

Unknown

Last updated

2024-01-08

For informational purposes only — not medical advice. Sourced from public registries and may not reflect the latest updates. Terms

Conditions

Attention Deficit Hyperactivity Disorder (ADHD) Mental and Behavioural Disorders

Interventions

Participants will first complete a brief online screening survey (<10 minutes). This information is used to assess eligibility and allocate participants to specific groups (e.g. those with and without

Eligibility

Sex/Gender

All

Inclusion criteria

Inclusion criteria: All participants: 1. Adults aged 18-35 years Healthy control participants (HC): 2. No diagnosis of ADHD and score on the Adult ADHD Self-Report Scale below the threshold indicative of ADHD. ADHD 3. Existing current diagnosis of ADHD and score on the Adult ADHD Self-Report Scale above the threshold indicative of ADHD. 4. Either not receiving ADHD medication and have not received any for a period of at least 3 months or receiving medication for ADHD (psychostimulant or non-stimulant) and adhering to this with a rate of at least 70%.

Exclusion criteria

Exclusion criteria: 1. Gluten or lactose intolerance, as participants will be asked to ingest a whey protein drink 2. Current or past diagnosis of nutritional, psychiatric (excluding ADHD) or neurological illnesses 3. Being pregnant/breastfeeding 4. Being a smoker (including e-cigarettes) 5. Currently taking medication known to affect the serotonergic system such as antidepressants 6. Learning disabilities 7. Following a restrictive diet (e.g. keto), as this might interfere with the experiment

Design outcomes

Primary

Measure	Time frame
Measured pre and post intervention (baseline and ~1 hour): 1. Attention measured using the computerised Test of Variable of Attention (TOVA) task (omission errors, response sensitivity, reaction time). 2. Motor impulsivity measured using the computerised Test of Variable of Attention (TOVA) task (commission errors). 3. Temporal impulsivity measured using the computerised Delay Discounting Task (indifference points, discounting function, area under the curve). 4. Cognitive impulsivity measured using the computerised Iowa Gambling Task (proportion of risky decisions, net score).	—

Measure

Time frame

Measured pre and post intervention (baseline and ~1 hour): 1. Attention measured using the computerised Test of Variable of Attention (TOVA) task (omission errors, response sensitivity, reaction time). 2. Motor impulsivity measured using the computerised Test of Variable of Attention (TOVA) task (commission errors). 3. Temporal impulsivity measured using the computerised Delay Discounting Task (indifference points, discounting function, area under the curve). 4. Cognitive impulsivity measured using the computerised Iowa Gambling Task (proportion of risky decisions, net score).

—

Secondary

Measure	Time frame
There are no secondary outcome measures	—

Countries

England, United Kingdom

Outcome results

None listed

Source: ISRCTN (via WHO ICTRP) · Data processed: Feb 7, 2026