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Mepergan Side Effects

Generic name: meperidine / promethazine

Medically reviewed by Last updated on Apr 7, 2023.

Note: This document contains side effect information about meperidine / promethazine. Some dosage forms listed on this page may not apply to the brand name Mepergan.

Applies to meperidine / promethazine: injectable solution, oral capsule.


Meperidine and promethazine can slow or stop your breathing, and may be habit-forming. MISUSE OF THIS MEDICINE CAN CAUSE ADDICTION, OVERDOSE, OR DEATH, especially in a child or other person using the medicine without a prescription.

Meperidine and promethazine should not be given to a child younger than 2 years old.

Do not use this medicine if you have used an MAO inhibitor in the past 14 days, such as isocarboxazid, linezolid, methylene blue injection, phenelzine, rasagiline, selegiline, or tranylcypromine.

Taking this medicine during pregnancy may cause life-threatening withdrawal symptoms in the newborn.

Fatal side effects can occur if you use this medicine with alcohol, or with other drugs that cause drowsiness or slow your breathing.

Get emergency medical help if you have signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat.

Like other opioid medicines, meperidine and promethazine can slow your breathing. Death may occur if breathing becomes too weak.

A person caring for you should seek emergency medical attention if you have slow breathing with long pauses, blue colored lips, or if you are hard to wake up.

Call your doctor at once if you have:

Seek medical attention right away if you have symptoms of serotonin syndrome, such as: agitation, hallucinations, fever, sweating, shivering, fast heart rate, muscle stiffness, twitching, loss of coordination, nausea, vomiting, or diarrhea.

Serious side effects may be more likely in older adults and those who are overweight, malnourished, or debilitated.

Long-term use of opioid medication may affect fertility (ability to have children) in men or women. It is not known whether opioid effects on fertility are permanent.

Common side effects may include:

This is not a complete list of side effects and others may occur. Tell your doctor about any unusual or bothersome side effect.

For Healthcare Professionals

Applies to meperidine / promethazine: injectable solution, oral capsule.


The most frequently observed meperidine adverse reactions have included light-headedness, dizziness, sedation, nausea, vomiting, and sweating. Somnolence is the most prominent CNS effect reported with promethazine.[Ref]

Nervous system


Common (1% to 10%): Lightheadedness, dizziness, sedation

Rare (less than 0.1%): Extrapyramidal reactions

Frequency not reported: Weakness, headache, tremor, uncoordinated muscle movements


Common (1% to 10%): Drowsiness

Frequency not reported: Sedation, somnolence, dizziness, confusion, extrapyramidal symptoms, lassitude, tremors, convulsive seizures, neuroleptic malignant syndrome[Ref]

Hyperexcitability and extrapyramidal movements have been reported following a single dose of promethazine.[Ref]



Frequency not reported: Euphoria, dysphoria, agitation, transient hallucinations and disorientation


Frequency not reported: Confusion, disorientation, euphoria, nervousness, insomnia, excitation, catatonic-like states, hysteria, hallucinations, nightmares, agitation, paradoxical reactions, hyperexcitability[Ref]

Hyperexcitability and abnormal movements have been reported following a single dose of promethazine.[Ref]



Frequency not reported: Respiratory depression, respiratory arrest


Frequency not reported: Asthma, respiratory depression, apnea, nasal stuffiness[Ref]



Common (1% to 10%): Nausea, vomiting

Frequency not reported: Dry mouth, constipation, biliary-tract spasm


Frequency not reported: Dry mouth, nausea, vomiting, jaundice[Ref]



Frequency not reported: Phlebitis, hypotension, tachycardia, bradycardia, palpitation, syncope, circulatory depression, shock, cardiac arrest, faintness


Frequency not reported: Tachycardia, bradycardia, increased or decreased blood pressure, faintness[Ref]



Common (1% to 10%): Sweating

Frequency not reported: Facial flushing


Frequency not reported: Dermatitis, photosensitivity, urticaria angioneurotic edema[Ref]



Frequency not reported: Tinnitus, vertigo[Ref]



Frequency not reported: Leukopenia, thrombocytopenia, thrombocytopenic purpura, agranulocytosis[Ref]



Frequency not reported: Visual disturbances


Frequency not reported: Blurred vision, diplopia


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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.