NutriStack
Fluoxetine and L-Tryptophan, a caution.
L-Tryptophan supplementation increases serotonin synthesis, and combined with fluoxetine's potent, long-lasting serotonin reuptake inhibition, can produce excessive serotonergic activity. Early case reports of this combination documented agitation, restlessness, and other serotonin syndrome symptoms.
One pair, every claim cited. The two substances, the type, the mechanism, the recommendation, and the primary literature.
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At a glance
- Substances
- Fluoxetine and L-Tryptophan
- Pair type
- Caution
- Evidence (highest tier)
- Moderate
- Source citations
- 1 source
- Stack Score effect
- −5 to your Stack Score (per scored caution row).
- Scope
- Supplement × Prescription
- Last verified
- May 30, 2026
Caution · Moderate evidence
Caution
What is happening. L-Tryptophan supplementation increases serotonin synthesis, and combined with fluoxetine's potent, long-lasting serotonin reuptake inhibition, can produce excessive serotonergic activity. Early case reports of this combination documented agitation, restlessness, and other serotonin syndrome symptoms.
Mechanism. Tryptophan is the rate-limiting precursor for serotonin synthesis via the tryptophan hydroxylase pathway. Supplemental tryptophan increases brain serotonin production. Fluoxetine's SERT blockade (with long half-life) prevents reuptake, causing dangerous accumulation of synaptic serotonin.
Recommendation. Avoid supplemental L-tryptophan with fluoxetine. This was one of the first reported SSRI-supplement serotonin syndrome interactions. Dietary tryptophan from food is not a concern.
Stack Score
How this pair moves the number.
Effect on the composite score
If both Fluoxetine and L-Tryptophan are in the same stack, this pair applies −5 to your Stack Score (per scored caution row).
The full algorithm, the clamping rules, and four worked stacks are documented at /methodology/stack-score.
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