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5-HTP and attention: grade C

Limited evidence. Direction: No effect.

C LimitedShort-term only

Educational guidance, not medical advice

Why this grade

Rubric condition met: One double-blind placebo RCT with no significant effect on its primary outcome; N needs a meta-analysis or a second independent, adequately sized null trial

A double-blind, placebo-controlled trial of a single 200 mg dose in 112 adults with high or low attention-deficit traits found no significant positive effect on any distractibility measure, its primary outcome, 90 minutes after dosing. On one N-back measure the placebo group improved and the 5-HTP group did not. The N-back task did not produce the expected distractor effect, and the authors call for more sensitive measures. One null trial is not enough for N.

How we grade evidence

Studies this grade rests on

The effect of 5-hydroxytryptophan, a serotonin precursor, on adults with high levels of Attention Deficit Hyperactivity Disorder traits: A randomised, controlled trial.

Jackson 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. PMID 42160304

Result not recorded
Design
Randomized, double-blind, placebo-controlled trial, single 200 mg dose
Sample
n = 112
Population
Adults with high (56) or low (56) levels of self-reported attention-deficit traits
Funding
not stated in the PubMed record or the full text we read

Search and history

Search (): (5-hydroxytryptophan[ti] OR 5-HTP[ti]) AND (fatigue[tiab] OR cognit*[tiab] OR exercise[tiab]) AND humans[mh] AND (clinical trial[pt] OR randomized controlled trial[pt])

  • Graded C (proposed): Proposed in the monograph draft
  • C to C (approved): Editor sign-off November 13, 2026: grade matches the editor-approved final page