Phenelzine Side Effects

Medically reviewed by Drugs.com. Last updated on Mar 7, 2025.

Applies to phenelzine: oral tablet.

Precautions

It is very important that your doctor check your progress at regular visits to allow for changes in your dose and to check for any unwanted effects.

You will also need to have your blood pressure measured before starting this medicine and while you are using it. If you notice any change to your recommended blood pressure, call your doctor right away. If you have questions about this, talk to your doctor.

When taken with certain foods, drinks, or other medicines, phenelzine can cause very dangerous reactions, such as sudden high blood pressure (also called hypertensive crisis). To avoid such reactions, follow these rules of caution:

• Do not eat foods that have dopamine and a high tyramine content (most common in foods that are aged or fermented to increase their flavor), such as cheese (especially strong or aged kinds), caviar, sour cream, liver, canned figs, soy sauce, sauerkraut, fava beans, yeasts, and yogurt. Avoid smoked or pickled meat, poultry, or fish, such as sausage, pepperoni, salami, anchovies, or herring. Do not eat dried fruit (such as raisins), bananas, avocados, raspberries, or very ripe fruit.
• Do not drink alcoholic beverages. This includes Chianti wine, sherry, beer, non-alcohol or low alcohol beer and wine, and liqueurs.
• Do not eat or drink too much caffeine. Caffeine can be found in coffee, cola, chocolate, tea, and many other foods and drinks. Ask your doctor how much caffeine is safe to use.

Phenelzine may cause some people to be agitated, irritable, or display other abnormal behaviors. It may also cause some people to have suicidal thoughts and tendencies or to become more depressed. If you or your caregiver notice any of these adverse effects, tell your doctor right away.

Call your doctor or hospital emergency room right away if you have a severe headache, stiff or sore neck, chest pains, fast heartbeat, sweating, dizziness, or nausea and vomiting while you are taking this medicine. These may be symptoms of a serious side effect called hypertensive crisis.

This medicine may cause blurred vision or make some people drowsy or less alert than they are normally. Make sure you know how you react to this medicine before you drive, use machines, or do anything else that could be dangerous if you are unable to see well or not alert.

This medicine will add to the effects of alcohol and other CNS depressants (medicines that slow down the nervous system, possibly causing drowsiness). Some examples of CNS depressants are antihistamines or medicine for hay fever, allergies, or colds; sedatives, tranquilizers, or sleeping medicine; prescription pain medicine or narcotics; medicine for seizures or barbiturates; muscle relaxants; or anesthetics, including some dental anesthetics. Check with your doctor before taking any of the above while you are using this medicine.

Dizziness, lightheadedness, or fainting may occur, especially when you get up suddenly from a lying or sitting position. Getting up slowly may help. When you get up from lying down, sit on the edge of the bed with your feet dangling for 1 or 2 minutes, then stand up slowly. If the problem continues or gets worse, check with your doctor.

Do not Stop taking phenelzine without checking first with your doctor. Your doctor may want you to gradually reduce the amount you are using before stopping it completely.

Before having any kind of surgery, dental treatment, or emergency treatment, tell the medical doctor or dentist in charge that you are using this medicine or have used it within the past 10 days. Taking phenelzine together with medicines that are used during surgery, dental, or emergency treatments may increase the risk of serious side effects.

Your doctor may want you to carry an identification card stating that you are using this medicine.

This medicine may affect blood sugar levels. If you are diabetic, be especially careful in testing for sugar in your blood or urine. If you have any questions about this, check with your doctor.

After you stop using this medicine, you must continue to exercise caution for at least 2 weeks with your foods, drinks, and other medicines, since these items may continue to react with phenelzine.

Do not take other medicines unless they have been discussed with your doctor. This includes prescription or nonprescription (over-the-counter [OTC]) medicines and herbal or vitamin supplements.

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:

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:

For healthcare professionals

Applies to phenelzine: oral tablet.

General adverse events

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]

Psychiatric

• 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]

Gastrointestinal

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

Genitourinary

• Common (1% to 10%): Anorgasmia, ejaculatory disturbances, impotence, sexual disturbances
• Uncommon (0.1% to 1%): Delayed ejaculation, difficulty in micturition, urinary retention^[Ref]

Other

• 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]

Cardiovascular

• 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]

Metabolic

• 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]

Ocular

• Common (1% to 10%): Blurred vision
• Uncommon (0.1% to 1%): Glaucoma, nystagmus
• Frequency not reported: Dilated pupils, photophobia^[Ref]

Musculoskeletal

• 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]

Hepatic

• 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]

Dermatologic

• Uncommon (0.1% to 1%): Pruritus, purpura, rash/skin rash, sweating
• Frequency not reported: Sweating with cold, clammy skin or fever^[Ref]

Hematologic

• Uncommon (0.1% to 1%): Blood dyscrasias
• Rare (less than 0.1%): Leucopenia^[Ref]

Immunologic

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

Respiratory

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

Hypersensitivity

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

Endocrine

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

See also:

Frequently asked questions

• What are some common side effects of antidepressants?

Further information

Phenelzine side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

Medical Disclaimer