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I've heard that mint tea can help with the symptoms of the common cold. In practice I find it generally can ease a cough/sore throat. I'm sure some of that is just drinking plenty of fluids, but does the mint actually have a medicinal effect? All of my googling has brought up semi-dubious results and I'd like something more than the anecdotal evidence of personal experience.

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Summary

Peppermint tea (and related: peppermint oil and menthol) has been studied as a treatment for a wide-range of conditions, and shows some potential to help in a number of them.

There are a number of hurdles that drugs must pass before they can be recommended for a particular condition - including safety and efficacy. Peppermint Tea hasn't passed those hurdles (with a minor exception that it is approved in Germany to treat indigestion).

2006 Review

A 2006 paper reviewed the evidence that was current at the time.

  • Diane L. McKay and Jeffrey B. Blumberg, A Review of the Bioactivity and Potential Health Benefits of Peppermint Tea ( Mentha piperita L.), Phytother. Res. 20, 619–633 (2006) DOI: 10.1002/ptr.1936

The key finding here:

However, human studies of peppermint leaf are limited and clinical trials of peppermint tea are absent. Adverse reactions to peppermint tea have not been reported, although caution has been urged for peppermint oil therapy in patients with GI reflux, hiatal hernia or kidney stones.

That doesn't mean there hasn't been evidence that it has some potential.

Non-human evidence related to colds

For example, the paper explains it has some anti-viral and anti-bacterial properties in tissue cultures (which is still a long way from saying it is safe and effective in humans). A 50% ethanol extract helped reduced sneezing in rats caused by an allergen. (See note at end.)

These results suggest that peppermint may be helpful in alleviating the nasal symptoms of allergic rhinitis.

Similarly, it have some effect as an antitussive (cough suppressant) in guinea pigs.

Human evidence related to colds

When it came to humans, there were some more interesting results:

Oral administration of 11 mg menthol (lozenges) did not decrease nasal decongestion in a randomized, double-blind, placebo-controlled trial of 62 subjects diagnosed with the common cold (Eccles et al., 1990), but did cause a marked change in nasal sensation of airflow with a subjective sensation of nasal decongestion.

I read this as saying it won't unblock your nose, but it will make it feel like your nose is unblocked, which may help you feel better.

It also may help with coughing:

Compared with placebo (pine oil or air), menthol did reduce coughing induced by inhalation of 33 µmol citric acid in 20 healthy subjects when given 5 min prior to each citric acid challenge (Morice et al., 1994), suggesting its effectiveness as an antitussive agent.

Conclusion

In summary, the paper covers a large number of (fairly minor?) potential benefits of peppermint tea, in dealing with minor complaints like sneezing, coughing, tension headaches, indigestion, irritable bowel syndrome and inflammation in humans, but the evidence falls short of being able to recommend peppermint tea as a safe and effective treatment or to recommend particular dosages.

The paper is admittedly 10 years old; perhaps more recent evidence has surfaced.

(Caution: The paper also shows that peppermint oil inhibits (non-heme) iron bioavailability, so care should be made to ensure iron consumption is high enough. There are no chronic toxicity studies in humans, but it shouldn't be used in patients with bile duct, gallbladder and liver disorders. Caution is also recommended for the use of peppermint oil capsules in patients with GI reflux, hiatal hernia or kidney stones.)


Note

In a comment, @called2voyage asked about the control for the 50% ethanol extract in experiment with the sneezing rats. That was a good question, and I wondered what the answer was so I explore it more here.

The McKay paper cites two papers:

  • Kamei C, Inoue T, Sugimoto Y, Masuda H. 2000. Effects of peppermint extracts on experimental allergic rhinitis in rats. Aroma Res 1: 61–66.

  • Inoue T, Sugimoto Y, Masuda H, Kamei C. 2001. Effects of peppermint ( Mentha piperita L.) extracts on experimental allergic rhinitis in rats. Biol Pharm Bull 24: 92–95. [PDF]

I was only able to find a copy of the latter, but given the dates and the same author list, I suspect it is sufficient.

The paper compares the sneeze rate and nasal rubbing of rats treated with:

  • "Control"
  • three different decreasing dosages of peppermint extract ("eluate") in 50% ethanol
  • "Tranilast"
  • "Saline"

(These are presented in decreasing order of sneezing/nasal rubbing.)

What does this mean?

The "happiest" rats were the ones that received saline. I was unable to see in the paper where it explicitly stated the definitions of "saline", but I believe it meant they never received the dose of the allergen - i.e. they had simple saline dripped into their noses, where the other rats had the allergen, ovalbumin (in saline) dripped into their noses.

The next happiest were the ones that were dosed with Tranilast, a "relatively safe and well tolerated" "antiallergic drug" (according to Wikipedia). So conventional medicine performed better than the peppermint oil.

The next happiest rats were the ones receiving the most most peppermint oil - there was a dose-response curve that suggests the peppermint oil was having some effect.

The least happy rats were the "Control". I would like to think the control was treated with a 50% ethanol solution, but I could not find any definition, and can't rule out that there was no treatment at all.

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    "A 50% ethanol extract helped reduced sneezing in rats caused by an allergen." How does this compare to 100% ethanol? – called2voyage Oct 12 '16 at 14:19
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    Or to 50% ethanol and 50% water. – called2voyage Oct 12 '16 at 14:19
  • @called2voyage: Good question that turned out to have an interesting answer, so I added it to the end. Thanks. – Oddthinking Oct 12 '16 at 15:45
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    Thanks, it is good to see more about their methods, though slightly dissatisfying that the "control" is not specified more. – called2voyage Oct 12 '16 at 15:47
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According to http://umm.edu/health/medical/altmed/herb/peppermint

Peppermint and its main active agent, menthol, are effective decongestants. Because menthol thins mucus, it is also a good expectorant, meaning it helps loosen phlegm and breaks up coughs. It is soothing and calming for sore throats (pharyngitis) and dry coughs.

The source given is McKay DL, Blumberg JB. A review of the bioactivity and potential health benefits of peppermint tea (Mentha piperita L.). Phytother Res. 2006;20:619-33. Review.

In vitro, peppermint has significant antimicrobial and antiviral activities, strong antioxidant and antitumor actions, and some antiallergenic potential. Animal model studies demonstrate a relaxation effect on gastrointestinal (GI) tissue, analgesic and anesthetic effects in the central and peripheral nervous system, immunomodulating actions and chemopreventive potential.

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    This is a tertiary (secondary?) source. It would be nice to quote the primary source of this claim. It isn't very convincing as is. – Oddthinking Oct 12 '16 at 6:46

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