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I had a pretty annoying dry cough a while ago following a cold. In the list of incredients for a cough syrup that I used, it said:

Each 5 mL or 1 teaspoonful (tsp.) contains:

  • DM | Cough Suppressant: Dextromethorphan Hydrobromide (15 mg): Controls dry cough.
  • E | Expectorant: Guaifenesin (200 mg): Relieves chest congestion.
  • Analgesic: Menthol (15 mg): Relieves sore throat pain.

Okay, seems straightforward enough.

But then I came across this reddit thread talking about an article titled "There is no evidence that cough medicine works" (posted in 2014).

Note that part of the article says:

It's important to understand that these studies have not proven that cough medicines don’t work. Rather, they’ve just found no proof that they do. It’s always possible that further studies could show that they help.

The comments in the reddit thread didn't seem to have any clear consensus about the validity of the article's claims, so I thought I'd ask here. I was wondering specifically about the Dextromethorphan. Is there any evidence that DM suppresses coughing?

  • 1
    +1. Just for anyone skimming over the text: The fact that DM seems to be as effective as a placebo does not mean that all cough medication has no effect. (Asthma Medication including β2-sympathomimetics are effective, as an example). For that to be proven, it needs a different answer - and a different question. – Narusan May 30 '18 at 16:04
  • Narusan-in-coma; b2 agonists aren't cough suppressants, so doesn't seem sensible to relate the not proven efficacy of a group of medication to the usefulness of another not related group. – whitebeltcoder May 31 '18 at 14:51
  • @whitebeltcoder Yes, but the quoted Reddit post talked about cough medicine in general. Hence my comment... – Narusan May 31 '18 at 15:51
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The bulk of the evidence says dextromethorphan (DM) is no better than placebo.

(2013) Do Cough Remedies Work?

Studies involving use of dextromethorphan in children have reported no clinically significant difference in symptoms of cough compared with placebo.[1] This lack of effect is not affected by dose, because studies of higher doses of dextromethorphan have also reported no difference in symptoms.[2] In adult patients with upper respiratory infection, there is no added benefit of using dextromethorphan or codeine.[3,4]

1. (2006) Child assessment of dextromethorphan, diphenhydramine, and placebo for nocturnal cough due to upper respiratory infection. https://www.medscape.com/medline/abstract/16928841
2. (2004) Dose-response relationship with increasing doses of dextromethorphan for children with cough. https://www.medscape.com/medline/abstract/15531013
3. (2000) Antitussive efficacy of dextromethorphan in cough associated with acute upper respiratory tract infection. https://www.medscape.com/medline/abstract/11045895

There is one study that found DM to be more effective than codeine, but it was very small (16 patients) and quite old (1983). It is not compelling.

2

What you've read seems to be the case, as this systematic review shows Cochrane review; there is no evidence for its use. There isn't evidence against its use either (I guess it hasn't shown security problems) but it doesn't seem sensible to spend your money or the health system's on medication with no evidence of efficacy.

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