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Dextromethorphan / promethazine Side Effects

Medically reviewed by Last updated on Mar 17, 2022.

For the Consumer

Applies to dextromethorphan / promethazine: oral solution, oral syrup


  • Do not give this drug to a child younger than 2 years of age. It may cause very bad and sometimes deadly breathing problems.
  • Use with care in children 2 years of age and older. Talk with the doctor.
  • Before your child takes this drug, tell the doctor if your child is taking any drugs that can cause breathing problems. There are many drugs that can do this. Ask the doctor or pharmacist if you are not sure.

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of high or low blood pressure like very bad headache or dizziness, passing out, or change in eyesight.
  • Fast or slow heartbeat.
  • Trouble passing urine.
  • Feeling very tired or weak.
  • Trouble controlling body movements, twitching, change in balance, trouble swallowing or speaking.
  • Hallucinations (seeing or hearing things that are not there).
  • Mood changes.
  • Ringing in ears.
  • Seizures.
  • Any unexplained bruising or bleeding.
  • Change in eyesight.
  • Feeling nervous and excitable.
  • Not able to sleep.
  • Yellow skin or eyes.
  • A very bad and sometimes deadly health problem called neuroleptic malignant syndrome (NMS) may happen. Call your doctor right away if you have any fever, muscle cramps or stiffness, dizziness, very bad headache, confusion, change in thinking, fast heartbeat, heartbeat that does not feel normal, or are sweating a lot.
  • This drug may cause very bad and sometimes deadly breathing problems. Call your doctor right away if you have slow, shallow, or trouble breathing.
  • Low white blood cell counts have rarely happened with this drug. This may lead to a higher chance of getting an infection. Tell your doctor if you have ever had a low white blood cell count. Call your doctor right away if you have signs of infection like fever, chills, or sore throat.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

  • Feeling sleepy.
  • Dizziness.
  • Dry mouth.
  • Upset stomach or throwing up.
  • Feeling tired or weak.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-332-1088. You may also report side effects at

For Healthcare Professionals

Applies to dextromethorphan/promethazine: oral syrup


The most common adverse reaction is somnolence.

Nervous system


Frequency not reported: Drowsiness, dizziness


Frequency not reported: Drowsiness, dizziness, sedation, somnolence, tremors, convulsive seizures, extrapyramidal symptoms such as oculogyric crisis, torticollis, and tongue protrusion, incoordination, neuroleptic malignant syndrome, serotonin syndrome, abnormal movements[Ref]



Frequency not reported: Asthma, nasal stuffiness, respiratory depression (potentially fatal), apnea[Ref]



Frequency not reported: Gastrointestinal disturbances


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



Frequency not reported: Disorientation, euphoria, nervousness, insomnia, excitation, catatonic-like states, hysteria, hallucinations, confusion, nightmares, delirium agitated behavior, hyperexcitability



Frequency not reported: Increased or decreased blood pressure, tachycardia, bradycardia, faintness[Ref]



Frequency not reported: Jaundice[Ref]



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



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



Frequency not reported: Angioneurotic edema[Ref]



Frequency not reported: Lassitude, tinnitus, fatigue[Ref]



Frequency not reported: Blurred vision, diplopia[Ref]


1. "Product Information. Promethazine DM (dextromethorphan-promethazine)." Par Pharmaceutical Inc (formerly Qualitest Pharmaceuticals Inc) (2008):

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.