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Phenelzine Side Effects

For the Consumer

Applies to phenelzine: oral tablet

As well as its needed effects, phenelzine may cause unwanted side effects that require medical attention.

Major Side Effects

If any of the following side effects occur while taking phenelzine, check with your doctor immediately:

More common:
  • Chills
  • cold sweats
  • confusion
  • dizziness, faintness, or lightheadedness when getting up from a lying or sitting position
  • overactive reflexes
  • shakiness in the legs, arms, hands, or feet
  • sudden jerky movements of the body
  • swelling
  • trembling or shaking of the hands or feet
Less common:
  • Abdominal or stomach pain
  • actions that are out of control
  • burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • change in consciousness
  • clay-colored stools
  • dark urine
  • decrease in frequency of urination
  • decrease in urine volume
  • difficult or troubled breathing
  • difficulty in passing urine (dribbling)
  • disorganized thoughts
  • dizziness
  • drowsiness
  • false or unusual sense of well-being
  • fast, pounding, or irregular heartbeat or pulse
  • fear or nervousness
  • fever
  • general feeling of discomfort, illness, or weakness
  • headache
  • high blood pressure
  • increased sweating
  • irregular, fast or slow, or shallow breathing
  • irritability
  • itching
  • lack of emotion or feelings
  • loss of appetite
  • loss of consciousness
  • loud or fast speech
  • low blood pressure
  • muscle tremors
  • muscle twitching
  • nausea or vomiting
  • nervousness
  • no emotion or expression in speech
  • painful urination
  • pale or blue lips, fingernails, or skin
  • rapid, deep, or shallow breathing
  • rash
  • restlessness
  • seeing or hearing things that are not there
  • seizures
  • shakiness and unsteady walk
  • shortness of breath
  • slow or irregular heartbeat
  • stomach cramps
  • sweating
  • swelling of the feet or lower legs
  • talking, feeling, and acting with excitement
  • uncontrolled eye movements
  • unpleasant breath odor
  • unsteadiness, trembling, or other problems with muscle control or coordination
  • unusual paleness
  • unusual tiredness or weakness
  • vomiting of blood
  • weakness
  • yellow eyes or skin

Minor Side Effects

Some phenelzine side effects may not need any medical attention. As your body gets used to the medicine these side effects may disappear. Your health care professional may be able to help you prevent or reduce these side effects, but do check with them if any of the following side effects continue, or if you are concerned about them:

More common:
  • Constipation
  • decreased interest in sexual intercourse
  • diarrhea
  • dry mouth
  • inability to have or keep an erection
  • indigestion
  • loss in sexual ability, desire, drive, or performance
  • loss of appetite
  • not able to have an orgasm
  • passing of gas
  • sleeplessness
  • stomach pain, fullness, or discomfort
  • trouble sleeping
  • unable to sleep
  • unusually deep sleep
  • unusually long duration of sleep
  • weight gain
Less common:
  • Blindness
  • blurred vision
  • decreased vision
  • eye pain
  • redness, swelling, or soreness of the tongue
  • tearing

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]


Common (1% to 10%): Postural hypotension
Uncommon (0.1% to 1%): Arrhythmias
Frequency not reported: Hypertensive crisis[Ref]


Common (1% to 10%): Gastrointestinal disturbances (nausea, vomiting, dryness of mouth, constipation)[Ref]


Common (1% to 10%): Weakness, fatigue, adverse effects on driving ability, tremors
Uncommon (0.1% to 1%): Jitteriness
Very rare (less than 0.01%): Transient respiratory and cardiovascular depression following ECT, fever associated with increased muscle tone
Frequency not reported: Withdrawal, withdrawal syndrome[Ref]

-Withdrawal may be associated with nausea, vomiting, and malaise.
-An uncommon withdrawal syndrome following abrupt drug discontinuation generally starts after 24 to 72 hours and may vary from vivid nightmares and agitation to frank psychosis and convulsions.
-Withdrawal syndrome generally responds to reinstitution of low dose therapy, followed by cautious downward titration and discontinuation.[Ref]

Nervous system

Common (1% to 10%): Dizziness, headache, drowsiness, sleep disturbances (including insomnia and hypersomnia), myoclonic movements, hyperreflexia
Uncommon (0.1% to 1%): Paresthesia, peripheral neuritis, convulsions, palilalia, nystagmus
Very rare (less than 0.01%): Ataxia, shock-like coma, neuroleptic malignant syndrome (occasionally fatal)[Ref]


Common (1% to 10%): Insomnia, anorgasmia
Uncommon (0.1% to 1%): Nervousness, euphoria, behavioral changes, confusion, hallucinations
Very rare (less than 0.01%): Toxic delirium, manic reaction, acute anxiety reaction, precipitation of schizophrenia
Frequency not reported: Suicidal ideation, suicidal behaviors[Ref]


Common (1% to 10%): Sexual disturbances (anorgasmia and ejaculatory disturbances)
Uncommon (0.1% to 1%): Difficulty in micturition, impotence and delayed ejaculation[Ref]


Uncommon (0.1% to 1%): Blood dyscrasias
Frequency not reported: Leukopenia[Ref]


Common (1% to 10%): Elevated serum transaminases
Uncommon (0.1% to 1%): Elevated liver enzymes
Very rare (less than 0.01%): Fatal progressive necrotizing hepatocellular damage, reversible jaundice[Ref]


Common (1% to 10%): Edema, weight gain
Uncommon (0.1% to 1%): Increased appetite, hypernatremia
Very rare (less than 0.01%): Hypermetabolic syndrome
Frequency not reported: Hyponatremia, inappropriate ADH secretion[Ref]


Common (1% to 10%): Twitching
Uncommon (0.1% to 1%): Muscle tremor[Ref]


Common (1% to 10%): Blurred vision
Uncommon (0.1% to 1%): Glaucoma[Ref]


Uncommon (0.1% to 1%): Sweating, rash, pruritus, purpura[Ref]


Very rare (less than 0.01%): Edema of the glottis[Ref]


Frequency not reported: Lupus-like illness[Ref]


1. Cerner Multum, Inc. "UK Summary of Product Characteristics." O 0

2. Cerner Multum, Inc. "Australian Product Information." O 0

3. "Product Information. Nardil (phenelzine)." Parke-Dvis, Morris Plains, NJ.

It is possible that some side effects of phenelzine may not have been reported. These can be reported to the FDA here. Always consult a healthcare professional for medical advice.

Disclaimer: Every effort has been made to ensure that the information provided is accurate, up-to-date and complete, but no guarantee is made to that effect. In addition, the drug information contained herein may be time sensitive and should not be utilized as a reference resource beyond the date hereof. This material does not endorse drugs, diagnose patients, or recommend therapy. This information is a reference resource designed as supplement to, and not a substitute for, the expertise, skill , knowledge, and judgement of healthcare practitioners in patient care. The absence of a warning for a given drug or combination thereof in no way should be construed to indicate safety, effectiveness, or appropriateness for any given patient. does not assume any responsibility for any aspect of healthcare administered with the aid of materials provided. The information contained herein is not intended to cover all possible uses, directions, precautions, warnings, drug interactions, allergic reactions, or adverse effects. If you have questions about the substances you are taking, check with your doctor, nurse, or pharmacist.