NutriStack
5-HTP and Mirtazapine, a caution.
Mirtazapine enhances serotonergic and noradrenergic transmission through alpha-2 antagonism. Adding 5-HTP increases serotonin production, creating risk of serotonin excess.
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At a glance
- Substances
- 5-HTP and Mirtazapine
- Pair type
- Caution
- Evidence (highest tier)
- Moderate
- Source citations
- 3 sources
- 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. Mirtazapine enhances serotonergic and noradrenergic transmission through alpha-2 antagonism. Adding 5-HTP increases serotonin production, creating risk of serotonin excess.
Mechanism. Mirtazapine blocks alpha-2 autoreceptors, enhancing serotonin and norepinephrine release. It also blocks 5-HT2A and 5-HT3 receptors. Adding 5-HTP increases serotonin production beyond what the compensatory mechanisms can handle.
Recommendation. Avoid combining 5-HTP with mirtazapine. While mirtazapine's mechanism differs from SSRIs, the serotonergic enhancement is still significant.
Sources (3)
- Boyer EW, Shannon M. The serotonin syndrome. N Engl J Med. 2005;352(11):1112-1120. PMID 15784664
- 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 Mirtazapine 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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