Meperidine / promethazine Side Effects

Not all side effects for meperidine / promethazine may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to meperidine / promethazine: injectable solution, oral capsule

Get emergency medical help if you have any of these signs of an allergic reaction while taking meperidine / promethazine: hives; difficulty breathing; swelling of your face, lips, tongue, or throat.

Stop using meperidine and promethazine and call your doctor at once if you have any of these serious side effects:

  • fast, slow, or uneven heartbeats;

  • shallow breathing;

  • extreme weakness or drowsiness;

  • feeling light-headed, fainting;

  • feeling anxious or agitated;

  • urinating less than usual;

  • tremors; or

  • unusual thoughts or behavior.

Less serious side effects of meperidine / promethazine may include:

  • constipation;

  • mild nausea or stomach upset;

  • warmth, tingling, or redness under your skin;

  • blurred vision; or

  • dry mouth.

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

Nervous system

Central nervous system side effects of meperidine may be either depressant or excitatory. Excitatory symptoms are sometimes ignored as possible side effects of meperidine, but may be due to the accumulation of a metabolite, normeperidine. Accumulation of normeperidine occurs more frequently in patients with renal insufficiency and in patients who are receiving meperidine via a patient-controlled analgesia pump.

Meperidine may increase intracranial pressure, and therefore should be used with caution in patients with head injuries. Severe adverse effects, such as respiratory depression, may be treated with the opioid antagonist naloxone.

A case of seizures has been reported in a patient with porphyria receiving meperidine.

Central nervous system adverse effects of meperidine include sleepiness, respiratory depression, delirium, seizures, tremors, dizziness, visual disturbances, muscle twitches, dilated pupils, and Parkinsonian symptoms.

Nervous system side effects are common with the use of promethazine and include excessive sedation, drowsiness, fatigue, paradoxical excitation, and decreased motor coordination. Extrapyramidal effects (including oculogyric crises, torticollis and tongue protrusion), encephalitic symptoms, convulsions, and psychosis have been rarely reported.


Psychiatric adverse effects of meperidine include fearfulness, agitation, paranoia, hypervigilance, and auditory and visual hallucinations.

Psychological dependence on meperidine may develop.


Meperidine may cause contraction of the sphincter of Oddi, thereby increasing intrabiliary pressure. As a result, meperidine may aggravate rather than relieve biliary colic.

Constipation is less common with meperidine than some other narcotics.

Gastrointestinal effects of meperidine including increased gastroesophageal reflux, increased biliary pressure, dry mouth, nausea, and vomiting have been reported.

Gastrointestinal effects of promethazine include nausea and vomiting.


There are case reports of bronchospasm occurring in patients with a history of asthma after receiving meperidine. Because of this effect and possible respiratory depression, meperidine should be used with caution in patients with severe reactive or obstructive pulmonary disease.

Bronchospasm has been reported with the use of meperidine in patients with underlying pulmonary disease.

Respiratory depression and arrest may occur rarely, especially with parenteral administration of promethazine. Equipment for resuscitation should be available when parenteral promethazine is used.


Cardiovascular effects including phlebitis have been reported in patients who are receiving meperidine. Hypotension has been reported rarely.

Cardiovascular effects have been rarely observed with the use of promethazine and include tachycardia, bradycardia, and transient hypotension. Prolongation of the QT interval, heart block, and malignant arrhythmias have been reported in association with other phenothiazines.

The hypotension reported in patients receiving meperidine occurs most commonly in patients who are under anesthesia, who are dehydrated, and who are receiving other medications.


Genitourinary effects including urinary retention have been reported in patients who are receiving meperidine.


Dermatologic effects including rash and sweating have been reported in patients who are receiving meperidine.


The neuroleptic malignant syndrome has been rarely observed during treatment with promethazine.

Fever, altered consciousness, autonomic dysfunction, and muscle rigidity are the hallmarks of the neuroleptic malignant syndrome. The neuroleptic malignant syndrome is associated with a case fatality rate of about 20%. Immediate discontinuation of promethazine and intensive monitoring and supportive care are indicated.


Inadvertent intra-arterial injection of promethazine carries a high risk of distal necrosis and frequently requires amputation of the affected limb. Subcutaneous injection has more rarely caused chemical irritation and necrosis.


Hypersensitivity reactions to promethazine include rare reports of rash, pruritus, hypotension, photosensitivity, and tachycardia.


Hematologic effects of promethazine include rare cases of neutropenia.


Immunologic reactions with the use of promethazine include rare reports of a systemic lupus erythematosus syndrome.


Central and obstructive apneas have been observed in infants given promethazine. Promethazine has been implicated by some as a possible cause of the Sudden Infant Death Syndrome (SIDS).

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