Supplements and Phenelzine.
Phenelzine, sold under the brand name Nardil, is a monoamine oxidase inhibitor (MAOI): it irreversibly inhibits MAO-A and MAO-B, with strict dietary and drug interaction rules.
Phenelzine is a monoamine oxidase inhibitor (MAOI). The class irreversibly inhibits MAO-A and MAO-B, raising synaptic monoamine levels. Current UK use is uncommon. It is confined to depression that has resisted other treatments and is managed in specialist psychiatry, because of the strict dietary rules (foods rich in tyramine) and drug interaction rules. The supplement surface is one of the most restrictive in clinical pharmacology. Anything serotonergic stacked on top can drive serotonin syndrome. St John's Wort, 5-HTP, tryptophan, SAMe, and saffron extract are all excluded. Anything sympathomimetic stacks on noradrenergic effect. Caffeine at high doses, yohimbe, bitter orange, ephedra (where available), and even excessive ginseng warrant care. Supplements rich in tyramine and certain protein extracts carry the same hypertensive crisis concern as the dietary tyramine rule. The psychiatric team is the gatekeeper for any new supplement on an MAOI regimen.
Below are the 8 documented pairs we have explicitly assessed against Phenelzine in the Distil database: 7 red and 1 amber. The pairs cluster around 2 mechanisms: MAOI pressor (blood-pressure surge) and Additive serotonergic activity. Every call is cited to either a clinical reference (PMID) or the British National Formulary. Anything not on this list is either still to be assessed or beyond our database scope. The checker beneath surfaces assessments by supplement, and the missing-item form at the bottom of the page routes any uncatalogued supplement into our next curation pass.
Documented interactions
MAOI pressor (blood-pressure surge)
L-Tyrosine is the raw material your body turns into adrenaline and noradrenaline. Phenelzine is an irreversible MAOI that blocks the breakdown of those same chemicals. Loading extra precursor while the breakdown pathway is shut off may push blood pressure up sharply, so we treat this as a do-not-combine pair without specialist sign-off.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
There is a published report of someone on the MAOI phenelzine developing headache, tremor and an over-elevated, restless mood after adding ginseng. The reason is not fully understood, but ginseng has mild stimulant-like effects on the nervous system that can clash with MAOIs. If you take phenelzine, do not start ginseng without talking to the doctor who manages your antidepressant.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Additive serotonergic activity
5-HTP raises serotonin levels. Combined with an MAOI like phenelzine, which blocks serotonin breakdown, this can produce severe serotonin syndrome. Do not combine.
Tryptophan is the building block your body uses to make serotonin, and phenelzine is an MAOI that blocks serotonin breakdown. Combining them can drive serotonin to dangerous levels and has caused toxic reactions in published cases. Do not combine.
Rhodiola appears to slow the same enzyme (monoamine oxidase) that phenelzine blocks. Stacking the two could push serotonin and related signals too high, risking serotonin syndrome or a dangerous rise in blood pressure. We treat this as a do-not-combine pair without specialist sign-off.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
SAMe raises serotonin-related activity, and phenelzine is an MAOI that blocks serotonin breakdown. Stacking the two could push serotonin too high, risking serotonin syndrome. We treat this as a do-not-combine pair without specialist sign-off.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
Saffron has its own antidepressant effect that appears to act on serotonin, and phenelzine is an MAOI that blocks serotonin breakdown. Stacking the two could push serotonin too high, risking serotonin syndrome. We treat this as a do-not-combine pair without specialist sign-off.
Reviewer-flagged: awaiting clinical-reviewer sign-off.
St John's Wort with an MAOI like phenelzine can cause hypertensive crisis and serotonin syndrome. This is a strict do-not-combine.
What this list does not say. Pairs not flagged here are not implicitly safe. They are either not yet in our database, or fall outside our inclusion scope (food-supplement interactions only; for drug-drug interactions, the BNF is authoritative). Use the checker below to surface any supplement, and submit a missing item if you take something we have not catalogued.
How we grade severity, choose what's in scope, and what we exclude.
Every call on this page is reasoned. We publish the full rubric for severity tiers, the medication inclusion logic, the evidence grades we accept, and what we deliberately leave out. About three thousand words. Worth reading once if you use this tool more than occasionally.
Read the full methodologyWant this checked across everything you take?
This page checks the pairs you enter. The personalised Distil report goes further:
- the same graded, cited interaction check across your whole stack, not just the pairs you thought to type in
- where your current routine may be leaving you short of your goals
- the evidence-backed compounds worth adding, and the ones worth dropping
It's a paid report: £79, or £49 for the first 25 customers. The interactions check is one section of it, and you can read a real one in full before you buy.
See a real sample reportSomething missing?
If a supplement or medication you take isn't in our autocomplete, tell us. We go through what people flag every week and add what's missing.