NutriStack
5-HTP and Fluoxetine, contraindicated.
5-HTP directly increases serotonin synthesis, while fluoxetine blocks serotonin reuptake. This combination can lead to serotonin syndrome. The risk is compounded by fluoxetine's long half-life, meaning serotonergic effects persist for weeks.
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At a glance
- Substances
- 5-HTP and Fluoxetine
- Pair type
- Contraindicated
- Evidence (highest tier)
- Moderate
- Source citations
- 3 sources
- Stack Score effect
- −25 to your Stack Score (per scored contraindication row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Contraindicated · Moderate evidence
Contraindicated
What is happening. 5-HTP directly increases serotonin synthesis, while fluoxetine blocks serotonin reuptake. This combination can lead to serotonin syndrome. The risk is compounded by fluoxetine's long half-life, meaning serotonergic effects persist for weeks.
Mechanism. 5-HTP bypasses tryptophan hydroxylase (the rate-limiting enzyme) to directly increase serotonin production. Fluoxetine and norfluoxetine block SERT for extended periods. The combination of increased serotonin synthesis and blocked reuptake creates dangerous serotonin excess.
Recommendation. Do not combine 5-HTP with fluoxetine. Due to fluoxetine's long half-life, wait at least 5 weeks after discontinuing fluoxetine before starting 5-HTP.
Sources (3)
- Birdsall TC. 5-Hydroxytryptophan: a clinically-effective serotonin precursor. Altern Med Rev. 1998;3(4):271-280. PMID 9727088
- Truyens M, Lobatón T, Ferrante M et al.. Effect of 5-Hydroxytryptophan on Fatigue in Quiescent Inflammatory Bowel Disease: A Randomized Controlled Trial. Gastroenterology. 2022. PMID 35940251
- Sutanto CN, Xia X, Heng CW et al.. The impact of 5-hydroxytryptophan supplementation on sleep quality and gut microbiota composition in older adults: A randomized controlled trial. Clinical Nutrition. 2024. PMID 38309227
Stack Score
How this pair moves the number.
Effect on the composite score
If both 5-HTP and Fluoxetine are in the same stack, this pair applies −25 to your Stack Score (per scored contraindication row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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