← All causality assessments
Causality: well established
Causality assessment · Causality: well established
Phenelzine and Serotonin syndrome: is the FAERS signal real?
A written Bradford Hill assessment of one drug–event pair. The grade is a judgement about the signal, not a statement that this drug causes this event in any one person; FAERS counts are reports, not rates.
Phenelzine ↔ Serotonin syndrome
n=36 co-reports · PRR 25.3 · ROR 25.9
Phenelzine is a monoamine-oxidase inhibitor; by blocking MAO-A it raises serotonin, noradrenaline, and dopamine, and combining it with any serotonergic drug (including SSRIs) can precipitate life-threatening serotonin syndrome — 36 co-reports here (PRR 25.3). This is why MAOIs carry strict dietary (tyramine) and drug-interaction restrictions, including a required washout when switching to or from SSRIs.
Regulatory basis: phenelzine prescribing information — serotonin syndrome; hypertensive crisis with tyramine; MAOI interaction warnings.
| Bradford Hill viewpoint | Status | Note |
|---|---|---|
| Temporality (necessary) | met | Onset within hours of a serotonergic combination |
| Strength | met | PRR 25.3, large |
| Consistency | met | Reproduced across MAOI cases |
| Specificity | partial | Not specific within serotonergic drugs |
| Biological gradient | met | Worse with higher combined load |
| Plausibility | met | Excess-serotonin mechanism |
| Coherence | met | Fits MAOI pharmacology |
| Experiment | met | Case series and dechallenge support it |
| Analogy | met | Analogous to other MAOI/SSRI combinations |
This table is this page's own qualitative read of the literature cited above, not an automated or citation-gated assessment — see the note at the bottom of this page.
✗ No ClinicalTrials.gov results-posting trial in the top search hits for phenelzine-sulfate captured serotonin syndrome as a tracked adverse event in a usable structure. Serotonin syndrome is a combination-triggered event that single-agent MAOI trials did not capture as a coded term.