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Dextromethorphan / diphenhydramine / phenylephrine Side Effects

Applies to dextromethorphan / diphenhydramine / phenylephrine: oral liquid.

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.

Use this medicine exactly as directed. Taking too much diphenhydramine can lead to serious heart problems, seizures, coma, or death.

Do not use this medicine to make a child sleepy. Ask a doctor before giving the medicine to a child younger than 4 years old.

Ask a doctor or pharmacist before using any other medicine that may contain diphenhydramine. Taking too much of this medicine can lead to a fatal overdose.

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

Stop using this medicine and call your doctor at once if you have:

  • severe drowsiness;

  • painful or difficult urination;

  • fast, pounding, or uneven heartbeats;

  • trouble breathing;

  • confusion, anxiety, irritability, tremors;

  • a seizure; or

  • problems with balance or speech.

Common side effects may include:

  • dizziness, drowsiness, headache;

  • blurred vision, dry eyes;

  • dry mouth, nose, or throat;

  • upset stomach, nausea, vomiting;

  • diarrhea, constipation; or

  • tiredness, trouble sleeping.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects.

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.