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Promethazine with Dextromethorphan Side Effects

Generic Name: dextromethorphan / promethazine

Note: This page contains side effects data for the generic drug dextromethorphan / promethazine. It is possible that some of the dosage forms included below may not apply to the brand name Promethazine with Dextromethorphan.

For the Consumer

Applies to dextromethorphan / promethazine: syrup

Check with your doctor if any of these most COMMON side effects persist or become bothersome:

Dizziness; drowsiness; dry mouth; nausea; stomach upset.

Seek medical attention right away if any of these SEVERE side effects occur while taking dextromethorphan / promethazine:

Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue); blurred vision; confusion; fainting; fast or irregular heartbeat; fever, chills, or sore throat; hallucinations; seizures; sensitivity to light; tremor; uncontrolled muscle movements; unusual bruising or bleeding; yellowing of skin or eyes.

For Healthcare Professionals

Applies to dextromethorphan / promethazine: oral syrup

Nervous system

Nervous system side effects have included tinnitus, drowsiness, dizziness, sedation, somnolence, confusion, disorientation, lassitude, incoordination, fatigue, euphoria, nervousness, insomnia, tremors, convulsive seizures, excitation, catatonic-like states, hysteria, hallucinations, and extrapyramidal symptoms such as oculogyric crisis, torticollis, and tongue protrusion[Ref]


Gastrointestinal side effects have included dry mouth, nausea, vomiting, and gastrointestinal disturbances.[Ref]


Cardiovascular side effect have included increased or decreased blood pressure, tachycardia, bradycardia, and faintness.[Ref]


Hepatic side effects have included jaundice.[Ref]


Hematologic side effects have included leukopenia, thrombocytopenia, thrombocytopenic purpura, and agranulocytosis.[Ref]


Dermatologic side effects have included dermatitis, photosensitivity, and urticaria.[Ref]


Respiratory side effects have included asthma, nasal stuffiness, respiratory depression (potentially fatal) and apnea (potentially fatal).[Ref]


Hypersensitivity side effects ave included angioneurotic edema.[Ref]


Other side effects have included neuroleptic malignant syndrome (potentially fatal).[Ref]

A potentially fatal symptom complex sometimes referred to as Neuroleptic Malignant Syndrome (NMS) has been reported in association with promethazine alone or in combination with antipsychotic drugs. Clinical manifestations of NMS are hyperpyrexia, muscle rigidity, altered mental status and evidence of autonomic instability (irregular pulse or blood pressure, tachycardia, diaphoresis and cardiac dysrhythmias). The diagnostic evaluation of patients with this syndrome is complicated. In arriving at a diagnosis, it is important to identify cases where the clinical presentation includes both serious medical illness (e.g., pneumonia, systemic infection, etc.) and untreated or inadequately treated extrapyramidal signs and symptoms (EPS). Other important considerations in the differential diagnosis include central anticholinergic toxicity, heat stroke, drug fever and primary central nervous system (CNS) pathology.

The management of NMS should include 1) immediate discontinuation of promethazine, antipsychotic drugs, if any, and other drugs not essential to concurrent therapy, 2) intensive symptomatic treatment and medical monitoring, and 3) treatment of any concomitant serious medical problems for which specific treatments are available. There is no general agreement about specific pharmacological treatment regimens for uncomplicated NMS. Since recurrences of NMS have been reported with phenothiazines, the reintroduction of promethazine should be carefully considered.[Ref]

Other side effects have included paradoxical reactions. Hyperexcitability and abnormal movements have been reported in patients following a single administration of promethazine. Consideration should be given to the discontinuation of promethazine and to the use of other drugs if these reactions occur. Respiratory depression, nightmares, delirium, and agitated behavior have also been reported in some of these patients.[Ref]


Ocular side effects have included blurred vision and diplopia.[Ref]


1. "Product Information. Promethazine DM (dextromethorphan-promethazine)." Vintage Pharmaceuticals Inc, Hunstville, AL.

It is possible that some side effects of Promethazine with Dextromethorphan 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.