Dextromethorphan (DELSYM, ROBITUSSIN DM) for Cough: More Reasons to Avoid It

The over-the-counter cough suppressant dextromethorphan (DELSYM, ROBITUSSIN DM) is widely available in cough and cold preparations, either alone on in com­bination with various decongestants, antihistamines and expectorants.
 
The editors of Worst Pills, Best Pills News have listed dextrometho­rphan as a Do Not Use drug because clinical trials have not found it to be effective and also because of growing evidence that dextromethorphan can have significant toxic effects, particularly when combined with some other medications.

Dextromethorphan may cause interactions because it modestly increases serotonin activity. This is rarely a problem when dextrometho­rphan is given in normal doses for a short time to people who are not taking other medications.

But when combined with drugs that strongly increase serotonin ef­fects, dextromethorphan can some­times produce dangerous reactions, such as serotonin syndrome.

Serotonin syndrome is a rare but serious condition that usually occurs when two or more drugs combine or interact to create too much serotonin in the body. In mild forms, the condition may be simply a nuisance. In severe cases, seizures, coma and death can occur. Symptoms of severe serotonin syndrome include jerking of muscles, rigid muscles, tremor, overactive reflexes, fever, sweating, shivering, confusion and agitation.

Another factor that can lead to in­teractions is when the person taking the drug is deficient in the enzyme CYP2D6, which metabolizes dex­tromethorphan. Millions of North Americans have this deficiency, and many millions more are taking medications that strongly inhibit the activity of CYP2D6.

Do not mix with ...

Dextromethorphan should not be taken with drugs that are called monoamine oxidase (MAO) inhibi­tors. These drugs include the anti­depressants phenelzine (NARDIL) and tranylcypromine (PARNATE), and the Parkinson’s disease drugs rasagiline (AZILECT) and selegiline (ELDEPRYL).

Serotonin syndrome has been re­ported when dextromethorphan was used with phenelzine.

The risk of combining dextromethorphan with other drugs that increase serotonin activity does not appear to be large, but given the minimal efficacy of dextrometho­rphan, even a modest risk is probably not worth taking.

Accordingly, patients taking any drug that increases serotonin blood levels should avoid dextrometho­rphan (See Table).

The antidepressants fluoxetine (PROZAC), paroxetine (PAXIL) and duloxetine (CYMBALTA) have the added problem of being moderate to potent inhibitors of CYP2D6. Such drugs are likely to increase dextromethorphan blood levels.

What You Can Do

The best way to avoid dex­tromethorphan drug interactions, of course, is to avoid taking dex­tromethorphan. It usually does not work very well anyway.

However, if you choose to take dextromethorphan, be particularly alert for evidence of serotonin toxic­ity when taking dextromethorphan concurrently with other serotonin active drugs.

Table. Drugs That Can Interact With Dextromethorphan to Increase Serotonin Levels

* Do Not Use on WorstPills.org
** Limited Use on WorstPills.org
*** Do Not Use Until Seven Years After Approval on WorstPills.org