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The main cough medicine I use (I am in Australia) contains Pentoxyverine as an active ingredient. The wikipedia article for this chemical states the outcome of reducing a cough, but curiously states no understood mechanism for this outcome:

Pentoxyverine suppresses the cough reflex in the central nervous system, but the exact mechanism of action is not known with certainty.

Wikipedia also says no clinical trials are available.

My initial research into cough medicines has turned up a whole host of skeptic websites claiming that studies show cough mixtures are ineffective at stopping a cough.

I understand that some medicines have been proven to work even though we do not understand their mechanism. But in this case the lack of an understood mechanism adds to my overall skepticism.

Does anyone know of any studies that assert whether this ingredient is effective or not?

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Brian Hinchey
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  • I heard that honey also works as a cough syrup; maybe it's just the texture of the stuff that soothes the throat and the rest is placebo – ratchet freak Mar 14 '12 at 23:28
  • My wife swears that cough syrups work and I am sure many others do. But I am trying to determine if any remedies have a scientifically described and proven mechanism. E.g. If honey does work, what is it about the texture that soothes the throat and how does soothing the throat stop the coughing. – Brian Hinchey Mar 14 '12 at 23:43
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    Define work(ie what symptoms is it supposed to treat) and find a claim that the cough syrups do treat that (those) symptom(s) and I will up vote. But as the question stands I think it is to vague to reasonably answer. Your problem may lie in unreasonable expectations. – Chad Mar 15 '12 at 13:09
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    @ratchetfreak I understand that [honey](http://en.wikipedia.org/wiki/Honey#In_medicine) is antiseptic and antibacterial. – ChrisW Mar 17 '12 at 01:44
  • @ChrisW: That's honey as it pertains to wounds, right? – Oddthinking Mar 17 '12 at 06:47
  • @ratchetfreak: [I've heard that too!](http://skeptics.stackexchange.com/questions/6002/does-honey-cure-or-alleviate-the-symptoms-of-a-common-cold) :-) – Oddthinking Mar 17 '12 at 06:47
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    This is too broad to have an answer really. It's like asking: "Do pain-killers work? I've tried aspirin and was not very effective...". Please restrict the question to one kind of cough suppressant molecule (e.g. "Pentoxyverine"). Thanks. – Sklivvz Mar 17 '12 at 10:43
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    The fact that a product's mechanism of action is not know does not make it inefficacious. For instance, lithium salts have been used for the treatment of bipolar disorders for decades, and still their mechanism of action is unknown. – nico Mar 17 '12 at 14:09
  • @nico Let me contradict you: that fact that neuro-psychiatrists don't know exactly how or why various medications work does make them less efficacious. If they knew, then they might be able to design other medications with fewer side-effects; and, they would know what they were treating! Currently there's no biological (neurological) test to determine which if any medication ought to benefit you. – ChrisW Mar 17 '12 at 15:38
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    @Oddthinking Honey wouldn't be the first thing I'd think of if I had a wound to manage (I'm not a doctor): just saying there may be more to honey than only texture. – ChrisW Mar 17 '12 at 16:44
  • @ChrisW: I think I was reacting to an attempt to explain a mechanism of an effect when we haven't even established the effect exists. I am not saying honey is not an antiseptic - highly sugared items can be - but that doesn't necessarily help a cough. – Oddthinking Mar 17 '12 at 23:18
  • @ChrisW: sure, but the is not my point. What I am saying is that a drug works in the same way whether you know its mechanism or not. One of the OP's point is that because the mechanism are not known pentoxyverine must be inefficacious, which is a bit of a fallacious conclusion. – nico Mar 18 '12 at 07:49
  • @nico: Actually I was just referring to the unknown mechanism as a possible red flag. I completely understand that there are many drugs where we have a scientifically proven outcome without the understood mechanism. When I get some time I am going to try and rewrite this question so that it is acceptable. – Brian Hinchey Mar 19 '12 at 09:46
  • Note: This question remained closed for over 12 months. I have substantially rewritten it, and narrowed the scope immensely onto one active ingredient, to allow it to be reopened. – Oddthinking May 20 '13 at 12:09
  • @Oddthinking looks like a good question now. But may not be answerable due to a lack of research. There *are* however Cochrane reviews on a variety of other cough medications, mostly inconclusive. Would broadening the question slightly to allow related compounds to be included improve it? – matt_black May 20 '13 at 20:12
  • @matt_black I am genuinely curious to know if any cough syrup variations have scientific backing and my original question was broad to represent that. However it was rewritten to be specific to a single variation at the moderator's request... – Brian Hinchey May 20 '13 at 23:53
  • According to Wikipedia entry you quote, the question is currently unanswerable: *"No controlled clinical trials regarding the efficiency of pentoyxverine are available."* – vartec May 21 '13 at 09:01
  • @vartec I appreciate that, but I wanted to reach out to the Skeptical community on this. Am I just being paranoid or are cough syrups just a placebo? If it is so obvious to us that there is no high quality clinical evidence for them, why do doctors keep recommending them to me whenever I get a cough! – Brian Hinchey May 22 '13 at 01:27

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TL/DR: There are no quality studies supporting the Pentoxyverine. The class of drugs that Pentoxyverine belongs to does not have strong support either.

Our good friends at the Cochrane Collaboration, who do high-quality meta-analyses, looked at over-the-counter cough medicines:

(Ambulatory settings roughly means medical care not in a hospital ward.)

They looked at twenty-five trials involving 3492 people (separating adults and children), and they looked at expectorants, antihistamines, antihistamine decongestants, antitussives, bronchodilators and guaifenesin.

Their conclusion:

The evidence for effectiveness of oral over-the-counter cough medicines is weak

Acute cough is a common and troublesome symptom in people who suffer from acute upper respiratory tract infection (URTI). Many people self-prescribe over-the-counter (OTC) cough preparations and health practitioners often recommend their use for the initial treatment of cough. The results of this review suggest that there is no good evidence for or against the effectiveness of OTC medications in acute cough. The results of this review have to be interpreted with caution because the number of studies in each category of cough preparations was small. Many studies were of low quality and very different from each other, making evaluation of overall efficacy difficult.

Now, there were no trials included that covered Pentoxyverine. However, Pentoxyverine is an antitussive, and there were a total of 8 trials that covered antitussives. So the class of drugs was tested, and did not provide clear evidence for or against, but the individual drug wasn't covered.

Further, looking at their selection criteria, any high-quality studies of Pentoxyverine should have been found and included. We can conclude that a careful search by these researchers for quality trials of Pentoxyverine found none.

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Oddthinking
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  • That's great to know! Especially when almost everyone I raise this issue with seems SO SURE that cough medicines help their cough. I'll be sure to push the point the next time a doctor tries to tell me to spend my money on a cough syrup... – Brian Hinchey Jun 19 '13 at 01:29
  • While having a similar discussion with a friend on Facebook, I unearthed [this 1977 trial](http://www.ncbi.nlm.nih.gov/pubmed/927305) comparing two different drug combinations, and finding one was better than the other: I am not sure why it didn't meet Cochrane's standards. (Or perhaps it did, but was countered by other studies.) – Oddthinking Jun 19 '13 at 01:34