For 137 years the creators of Listerine have been claiming the mouthwash can cure gonorrhoea.
Researchers at Monash University in Melbourne decided to finally test it out (because no one else ever had, apparently), and preliminary results show the century-old claim may have legs, after all.
As far back as 1879, and before the advent of antibiotics, the manufacturer of Listerine, a commercial brand of mouthwash, claimed that it could be used to cure gonorrhoea. But no published research has tested out this claim.
In a bid to rectify this, the researchers assessed whether Listerine could curb the growth of N gonorrhoeae in laboratory tests and in a clinical trial.
For the laboratory tests, different dilutions (up to 1:32) of Listerine Cool Mint and Total Care, both of which contain 21.6 per cent alcohol, were applied to cultures of N gonorrhoeae to see which of any of them might curb growth of the bacteria. By way of a comparison, a salt water (saline) solution was similarly applied to an identical set of cultures.
Listerine at dilutions of up to 1 in 4, applied for 1 minute, significantly reduced the number of N gonorrhoeae on the culture plates, whereas the saline solution did not.
The clinical trial involved 196 people who had previously tested positive for gonorrhoea in their mouths/throat, and who were returning for treatment at one sexual health clinic in Melbourne, Australia, between May 2015 and February 2016. Almost a third tested positive for the bacteria in their throat on the return visit.
33 people were randomly assigned to a rinse and gargle with Listerine and 25 people to a rinse and gargle with the saline solution.
After rinsing and gargling for 1 minute, the proportion of viable gonorrhoea in the throat was 52 per cent among those using Listerine compared with 84 per cent among those using saline. And those using Listerine were 80 per cent less likely to test positive for gonorrhoea in their throat five minutes after gargling than were those using the saline solution.
The researchers admit that the monitoring period was short, so the possibility that the effects of the mouthwash might be short-lived can't be ruled out. But the laboratory test results would suggest otherwise, they say.
This research is preliminary, so a larger trial is currently under way to confirm these results and see whether the use of mouthwash could curb the spread of gonorrhoea, they say.
"If daily use of mouthwash was shown to reduce the duration of untreated infection and/or reduce the probability of acquisition of N gonorrhoeae, then this readily available and low cost intervention may have very significant public health implications in the control of gonorrhoea." write the researchers.