L-theanine and Paraxanthine for Cognitive Improvement in Adults With ADHD and ASD

NCT07189442 | Recruiting

• 1 other identifier: IRB2025-147
• Study Type: interventional
• Target: 24
• Locations: 1 country
• Sites: 1

Brief Summary

This pilot study will test whether combining L-theanine and paraxanthine improves sustained attention, inhibitory control, and overall cognition in adults with ADHD and ASD. Two parallel randomized, single-blinded, repeated-measures crossover trials will be conducted. Participants will complete neuropsychological testing, fMRI scanning, and self-report measures following administration of the L-theanine-paraxanthine combination compared to placebo.

Conditions

Attention Deficit Hyperactivity Disorder (ADHD); Autism Spectrum Disorder (ASD)

Keywords

ADHD; Attention Deficit Hyperactivity Disorder; ASD; Autism spectrum disorder; Autism

Outcome Measures

Primary Outcomes (3)

• fMRI task-related activity

  fMRI task-related activity in default mode and central executive networks during Go/NoGo and Stop-Signal tasks.

  At visit 2 or 3, 30 minutes after intake of L-theanine-paraxanthine or placebo.

• Stop Signal Reaction Time

  Estimated time (milliseconds) required to inhibit a prepotent response following a stop signal, computed using the horse-race model and drift-diffusion theory. Lower values indicate better inhibitory control.

  At visit 2 or 3, 30 minutes after intake of L-theanine-paraxanthine or placebo. This task is performed while in the MRI.

• d-prime (sensitivity to the Go signal)

  d-prime on Go/No-Go task computed using the signal detection theory.

  At visit 2 or 3, 30 minutes after intake of L-theanine-paraxanthine or placebo. This task is performed while in the MRI.

Study Arms (2)

Attention deficit hyperactivity disorder (ADHD)

EXPERIMENTAL

A group of 12 adult males with Attention Deficit Hyperactivity Disorder (ADHD) will be enrolled. Each participant will receive both study conditions in a randomized, single-blinded, repeated-measures crossover design: Active Condition: One capsule containing 200 mg L-theanine + 200 mg paraxanthine. Placebo Condition: One capsule containing 400 mg of corn starch. The order of administration will be randomized, with each participant completing both conditions on separate visits (visits 2 and 3).

Dietary Supplement: L-theanine and paraxanthine; Dietary Supplement: Placebo

Autism spectrum disorder (ASD)

EXPERIMENTAL

A group of 12 adult males with autism spectrum disorder (ASD) will be enrolled. Each participant will receive both study conditions in a randomized, single-blinded, repeated-measures crossover design: Active Condition: One capsule containing 200 mg L-theanine + 200 mg paraxanthine. Placebo Condition: One capsule containing 400 mg of corn starch. The order of administration will be randomized, with each participant completing both conditions on separate visits (visits 2 and 3).

Dietary Supplement: L-theanine and paraxanthine; Dietary Supplement: Placebo

Interventions

Placebo DIETARY_SUPPLEMENT

400 mg corn starch capsule

Attention deficit hyperactivity disorder (ADHD); Autism spectrum disorder (ASD)

L-theanine and paraxanthine DIETARY_SUPPLEMENT

200 mg L-theanine + 200 mg paraxanthine capsule

Attention deficit hyperactivity disorder (ADHD); Autism spectrum disorder (ASD)

Eligibility Criteria

• Sex: male
• Healthy Volunteers: No
• Age Groups: Child (0-17), Adult (18-64), Older Adult (65+)

You may qualify if:

• Adults (18+ years) diagnosed by a physician (per self-report) with ADHD or ASD
• \* Participants with a dual diagnosis and ASD and ADHD will be recruited but will only be included in the ASD group - their concurrent ADHD diagnosis will be included as an additional variable in exploratory analyses

You may not qualify if:

• Subjects with gross visual or auditory impairments that might limit their ability to perform neuropsychological tasks
• Inability to read and follow written instructions
• Physical, neurological, intellectual, or psychiatric impairments (except ADHD or ASD) that could affect cognitive and motor functions
• Subjects on medications including antidepressants and antipsychotics that may affect performance in the tasks
• Subjects on medications that are likely to interact with the administered substances, including regular intake of medication that could alter visual, auditory, cognitive, or motor functions (except stimulants)
• History of head injury resulting in loss of consciousness/history of brain surgery
• Subjects who have developed adverse effects when caffeine/paraxanthine /L-theanine/corn starch (will be in placebo) containing products were consumed
• Subjects who are unwilling or unable to refrain from intake of L-theanine/ caffeine/ paraxanthine containing food or beverages within the 24 hours prior to each study visit
• Intake of drugs containing caffeine, other phosphodiesterase inhibitors, or adenosine receptor blockers within the past 3 months
• Intake of medications known to have pharmacological interactions with paraxanthine within the past 3 months
• Current/past diagnosis of tics or other forms of dyskinesia
• History of headache, drowsiness, anxiety, insomnia, or nausea following intake of caffeine or caffeine-containing beverages
• Current/past history of smoking and/or alcohol or drug abuse
• Subjects with absolute contraindications to undergo MRI after being screened by the TTNI safety screening sheet (Appendix)
• Unwillingness or inability to entirely refrain from the use of electronic devices during study visits

Sponsors & Collaborators

• Texas Tech University Health Sciences Center: lead
• Texas Tech University: collaborator

Study Sites (1)

Texas Tech University

Lubbock, Texas, 79430, United States

RECRUITING

MeSH Terms

Conditions

Attention Deficit Disorder with Hyperactivity; Autism Spectrum Disorder; Autistic Disorder

Interventions

theanine; 1,7-dimethylxanthine

Condition Hierarchy (Ancestors)

Attention Deficit and Disruptive Behavior Disorders; Neurodevelopmental Disorders; Mental Disorders; Child Development Disorders, Pervasive

Central Study Contacts

Chathurika S Dhanasekara, MD, PhD

CONTACT

806-743-2378; samudani.dhanasekara@ttuhsc.edu

Chanaka N Kahathuduwa, MD, PhD

CONTACT

806-412-9974; chanaka.kahathuduwa@ttuhsc.edu

Study Design

• Study Type: interventional
• Phase: not applicable
• Allocation: RANDOMIZED
• Masking: SINGLE
• Who Masked: PARTICIPANT
• Masking Details: Single (Participant and outcomes assessors blinded; study staff preparing capsules unblinded)
• Purpose: OTHER
• Intervention Model: CROSSOVER
• Sponsor Type: OTHER
• Responsible Party: PRINCIPAL INVESTIGATOR
• PI Title: Assistant Professor

Model Details: Crossover Assignment (two-way, repeated measures)

Study Record Dates

• First Submitted: September 16, 2025
• First Posted: September 24, 2025
• Study Start: October 1, 2025
• Primary Completion (Estimated): June 1, 2026
• Study Completion (Estimated): June 1, 2026
• Last Updated: February 5, 2026

Record last verified: 2026-02

Data Sharing

• IPD Sharing: Will not share

Locations

US (1)