Skip to main content

Phenelzine Side Effects

Medically reviewed by Last updated on Feb 16, 2023.

Applies to phenelzine: oral tablet.


Oral route (Tablet)

Antidepressants increased the risk compared to placebo of suicidal thinking and behavior (suicidality) in children, adolescents, and young adults in short-term studies of major depressive disorder (MDD) and other psychiatric disorders. Anyone considering the use of phenelzine sulfate or any other antidepressant in a child, adolescent, or young adult must balance this risk with the clinical need. Short-term studies did not show an increase in the risk of suicidality with antidepressants compared to placebo in adults beyond age 24; there was a reduction in risk with antidepressants compared to placebo in adults aged 65 and older. Depression and certain other psychiatric disorders are themselves associated with increases in the risk of suicide. Patients of all ages who are started on antidepressant therapy should be monitored appropriately and observed closely for clinical worsening, suicidality, or unusual changes in behavior. Families and caregivers should be advised of the need for close observation and communication with the prescriber. Phenelzine sulfate is not approved for use in pediatric patients.

Serious side effects of Phenelzine

Along with its needed effects, phenelzine may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking phenelzine:

More common

Less common

Other side effects of Phenelzine

Some side effects of phenelzine may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

Less common

For Healthcare Professionals

Applies to phenelzine: oral tablet.


The most important adverse event reported is hypertensive crisis, which has been associated with intracranial bleeding and has been fatal.[Ref]

Nervous system

Common (1% to 10%): Dizziness, drowsiness, headache, hyperreflexia, myoclonic movements, tremors

Uncommon (0.1% to 1%): Convulsions, palilalia, paresthesia, peripheral neuritis

Rare (0.01% to 0.1%): Acute dystonic reaction, ataxia, coma, neuroleptic malignant syndrome (occasionally fatal), sensorimotor peripheral neuropathy, shock-like coma, speech blockade, transient respiratory and cardiovascular depression following ECT

Frequency not reported: Intracranial bleeding/fatal intracranial bleeding, occipital headache/occipital headache which may radiate frontally[Ref]


Common (1% to 10%): Anorgasmia, hypersomnia, hypomania, insomnia, sleep disturbances

Uncommon (0.1% to 1%): Agitation, behavioral changes, confusion, euphoria, frank psychosis, hallucinations, nervousness, vivid nightmares

Rare (0.01% to 0.1%): Acute anxiety reaction, delusional parasitosis, manic reaction, precipitation of schizophrenia, toxic delirium

Frequency not reported: suicidal behaviors, suicidal ideation[Ref]


Common (1% to 10%): Constipation, dry mouth, gastrointestinal disturbances, nausea, vomiting[Ref]


Common (1% to 10%): Anorgasmia, ejaculatory disturbances, impotence, sexual disturbances

Uncommon (0.1% to 1%): Delayed ejaculation, difficulty in micturition, urinary retention[Ref]


Common (1% to 10%): Adverse effects on driving ability, fatigue, weakness

Uncommon (0.1% to 1%): Jitteriness, withdrawal/withdrawal syndrome

Rare (less than 0.1%): Fever associated with increased muscle tone, hyperpyrexia, malaise[Ref]

Withdrawal may be associated with nausea, vomiting, and malaise.

Withdrawal syndrome occurred after abrupt drug discontinuation, and generally started after 24 to 72 hours; signs/symptoms varied from vivid nightmares and agitation to frank psychosis and convulsions. The withdrawal syndrome generally responded to reinstitution of low dose therapy, followed by cautious downward titration and discontinuation.[Ref]


Common (1% to 10%): Edema, postural hypotension

Uncommon (0.1% to 1%): Arrhythmias

Rare (0.01% to 0.1%): Blood pressure changes, tachycardia

Frequency not reported: Bradycardia, constricting chest pain, hypertensive crisis, palpitation[Ref]


Common (1% to 10%): Weight gain

Uncommon (0.1% to 1%): Hypernatremia, increased appetite

Rare (0.01% to 0.1%): Hypermetabolic syndrome, metabolic acidosis

Frequency not reported: Hyponatremia[Ref]

Hyponatremia may be more likely to occur in older patients or in those with inappropriate secretion of antidiuretic hormone; this side effect should be considered in patients treated with antidepressants who present with confusion, convulsions, and/or drowsiness.

Hypermetabolic syndrome may resemble signs/symptoms of an overdose.[Ref]


Common (1% to 10%): Blurred vision

Uncommon (0.1% to 1%): Glaucoma, nystagmus

Frequency not reported: Dilated pupils, photophobia[Ref]


Common (1% to 10%): Twitching

Uncommon (0.1% to 1%): Muscle tremor

Rare (0.01% to 0.1%): Elevated creatine kinase levels, muscular rigidity

Frequency not reported: Neck soreness, neck stiffness[Ref]


Common (1% to 10%): Elevated serum transaminases (without accompanying signs/symptoms)

Uncommon (0.1% to 1%): Elevated liver enzymes

Rare (less than 0.1%): Fatal progressive necrotizing hepatocellular damage, reversible jaundice[Ref]


Uncommon (0.1% to 1%): Pruritus, purpura, rash/skin rash, sweating

Frequency not reported: Sweating with cold, clammy skin or fever[Ref]


Uncommon (0.1% to 1%): Blood dyscrasias

Rare (less than 0.1%): Leucopenia[Ref]


Uncommon (0.1% to 1%): Lupus-like illness[Ref]


Rare (0.01% to 0.1%): Hypoxia, tachypnea[Ref]


Rare (0.01% to 0.1%): Edema of the glottis[Ref]


Rare (0.01% to 0.1%): Inappropriate secretion of antidiuretic hormone/ADH secretion[Ref]

Frequently asked questions


1. Product Information. Nardil (phenelzine). Parke-Davis. 2001;PROD.

2. Cerner Multum, Inc. UK Summary of Product Characteristics.

3. Cerner Multum, Inc. Australian Product Information.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.