5-HYDROXYTRYPTOPHAN, A SEROTONIN PRECURSOR, AS A NOVEL TREATMENT FOR ADULTS WITH ATTENTION DEFICIT HYPERACTIVITY DISORDER: A RANDOMISED, DOUBLE-BLIND TRIAL

Despite the existence of several pharmacotherapies for ADHD, current medications carry high abuse risks, and many patients seek alternative options. One possibility for new therapies is serotonergic intervention; serotonin plays a critical role in mood regulation, sleep, and orienting attention. Furthermore, lower levels of circulating serotonin and serotonergic metabolites have been observed in ADHD individuals, suggesting a potential issue in serotonin synthesis. This experiment assessed the efficacy of 5-hydroxytryptophan, a serotonin precursor, in reducing the core ADHD trait of distractibility.
112 non-clinical participants completed a randomised, double-blind trial with a 2(intervention: placebo or 200mg 5-hydroxytryptophan) x2(group: high ADHD traits or low ADHD traits) x2(time: pre and 90 minutes post-administration) design. Participants completed the Adult ADHD Self-Report Scale Screener and were partitioned into high (score ≥ 4, n = 56) and low (scores ≤ 1, n = 56) groups. Distractibility was assessed using reaction time and accuracy in a task-relevant (flanker) and task-irrelevant (N-back coupled with auditory stimuli) distractor. Efficacy was assessed using 2x2x2 ANOVA at 5% 2-tailed significance.
Contrary to previous reports, flanker and n-back results revealed only small, non-significant performance differences between high- and low-ADHD groups pre-intervention. Whilst 5-hydroxytryptophan administration produced a small decrease in reaction time, similar decreases were seen in the placebo condition. Overall, three-way interaction between intervention, group, and time was non-significant (F(1,108)=0.409, p=0.524).
5-Hydroxytryptophan supplementation was not found to improve or impair distractibility in any measure for individuals with high or low ADHD traits. Future work should consider traits more sensitive to ADHD status to assess efficacy.