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What the label lists and what reports show

Phenelzine side effects

Phenelzine's FDA label lists its adverse reactions in its own words. FAERS holds 1,563 reports naming it through July 30, 2026; the reaction reported most often, leaving out the conditions it is used for, product-use terms and outcomes, is headache (138 reports).

  • Generic listed
  • Boxed warning

Check it at the source: the phenelzine FDA label on DailyMed (effective June 6, 2025, Parke-Davis Div of Pfizer Inc); the FDA FAERS public dashboard.

What does the label list?

From the label: adverse reactions

NARDIL is a potent inhibitor of monoamine oxidase. Because this enzyme is widely distributed throughout the body, diverse pharmacologic effects can be expected to occur. When they occur, such effects tend to be mild or moderate in severity (see below), often subside as treatment continues, and can be minimized by adjusting dosage; rarely is it necessary to institute counteracting measures or to discontinue NARDIL. Common side effects include: Nervous System –Dizziness, headache, drowsiness, sleep disturbances (including insomnia and hypersomnia), fatigue, weakness, tremors, twitching, myoclonic movements, hyperreflexia. Gastrointestin al–Constipation, dry mouth, gastrointestinal disturbances, elevated serum transaminases (without accompanying signs and symptoms). Metabolic –Weight gain. Cardiovascular –Postural hypotension, edema. …

Source: FDA drug label, Parke-Davis Div of Pfizer Inc, effective June 6, 2025 (SPL set 513a41d0-37d4-4355-8a6d-a2c643bce6fa), via openFDA; the full label on DailyMed

What do FAERS reports show?

1,563 reports list phenelzine among the medicines taken, each a report of something that happened, not proof the medicine caused it; 41 are coded as a death and 331 as a hospital stay. Counts follow how widely a medicine is used and watched, and they are not a measure of how risky it is. Of the 20 reactions below, 7 are named by the same term (in US spelling) in the label's adverse reactions, warnings or patient leaflet; a reaction the label does not name may still be there under another word, and a report does not show that the medicine caused it.

Reports received each year

The 25 most reported reactions

  • Drug Ineffective (a use or a product term, not a reaction)330
  • Depression (a use or a product term, not a reaction)187
  • Headache (named in the label)138
  • Anxiety (a use or a product term, not a reaction)129
  • Weight Increased122
  • Insomnia (named in the label)104
  • Drug Interaction (a use or a product term, not a reaction)100
  • Dizziness (named in the label)99
  • Pharmaceutical Product Complaint97
  • Fatigue (named in the label)94
  • Feeling Abnormal89
  • Malaise78
  • Nausea78
  • Hypertension77
  • Fall61
  • Somnolence57
  • Weight Decreased56
  • Condition Aggravated (a use or a product term, not a reaction)52
  • Asthenia51
  • Suicidal Ideation (named in the label)51
  • Tremor (named in the label)49
  • Diarrhoea44
  • Drug Withdrawal Syndrome44
  • Drug Effect Decreased43
  • Hypotension (named in the label)42

Source: FDA Adverse Event Reporting System (FAERS) via openFDA, reports through July 30, 2026; reactions as MedDRA preferred terms

What next?

Phenelzine: the full record
label, generics, price, shortages, recalls
Side effects hub
the most reported medicines and reactions