Delsym XR Side Effects: What to Expect and When to Call Your Doctor

Delsym XR is one of the most widely used OTC cough suppressants in the United States — and for good reason. Most people tolerate it very well. But like any medication, dextromethorphan (the active ingredient) can cause side effects, and a small number of interactions can be serious. Here's what you need to know before taking Delsym XR.

Common Side Effects of Delsym XR

Most people who take Delsym XR at the recommended dose experience few or no side effects. When side effects do occur, the most common are:

• Nausea: The most frequently reported side effect. Taking Delsym XR with a small amount of food may help reduce nausea.
• Stomach upset or stomach pain: Mild GI discomfort that typically resolves on its own.
• Dizziness (rare): Some people feel lightheaded, especially at higher doses. Avoid driving or operating machinery if this occurs.
• Drowsiness (rare): Unlike some older cough medicines that contain antihistamines (like diphenhydramine), dextromethorphan is not primarily sedating. Drowsiness can occur but is less common than with antihistamine-based products.

These common side effects are typically mild and do not require stopping the medication. If nausea or dizziness is significant, try taking Delsym XR with a light snack.

Serious Side Effects: Know the Warning Signs

While rare at normal doses, serious side effects can occur — particularly if Delsym XR is taken with certain other medications.

Serotonin Syndrome

This is the most serious drug interaction risk with Delsym XR. Serotonin syndrome can occur when dextromethorphan is combined with MAOIs (monoamine oxidase inhibitors), SSRIs, SNRIs, St. John's Wort, or other serotonergic drugs. DXM is a weak serotonin reuptake inhibitor; when combined with drugs that also increase serotonin, the levels in the body can become dangerously high.

Symptoms of serotonin syndrome include:

• Agitation, confusion, or restlessness
• Rapid heart rate and high blood pressure
• Fever and sweating
• Muscle twitching, tremors, or stiffness
• Seizures (in severe cases)

If you experience any of these symptoms after taking Delsym XR, call 911 or go to the emergency room immediately. Do NOT combine Delsym XR with an MAOI drug — this combination can be fatal. Wait at least 14 days after stopping an MAOI before taking any DXM product.

Signs of Overdose

Taking more than the recommended amount of Delsym XR can cause overdose symptoms. At supratherapeutic doses, dextromethorphan acts as a dissociative substance and can cause:

• Hallucinations and extreme confusion
• Rapid or irregular heartbeat
• Slow, shallow breathing
• Seizures
• Loss of consciousness

If you suspect a DXM overdose, call Poison Control at 1-800-222-1222 or call 911 immediately. Adults should not exceed 120 mg of dextromethorphan in a 24-hour period.

What Side Effects Are Normal vs. When to Call Your Doctor

Normal (monitor, no urgent action): Mild nausea, mild stomach upset, slight drowsiness or dizziness

Call your doctor: Cough that returns or worsens after 7 days; cough accompanied by fever, rash, or persistent headache; symptoms that suggest a secondary infection

Call 911 / go to the ER: Any signs of serotonin syndrome; suspected overdose; difficulty breathing; rapid or irregular heart rate; seizures; loss of consciousness

Special Populations: Extra Caution Needed

• Children under 4: Do not give any DXM product. Not approved and can cause serious adverse effects.
• Pregnant or breastfeeding: Ask a healthcare professional before use. Safety has not been fully established.
• Liver disease: Dextromethorphan is primarily metabolized by the liver (CYP2D6). Use with caution in patients with significant hepatic impairment.

For a full list of drug interactions, see: Delsym XR drug interactions: What to avoid and what to tell your doctor.

If you're having trouble finding Delsym XR at your pharmacy, medfinder can help you locate it in stock near you.