Daily use of Listerine mouthwash may help prevent the spread of some cases of gonorrhoea, according to results from a new study.
Researchers discovered that a diluted solution of the mouthwash curbed the growth of Neisseria gonorrhoeae, the bacteria responsible for the sexually transmitted disease, following the results of a laboratory experiment as well as a clinical trial involving men who have sex with men.
“[These] data suggest Listerine significantly reduces the amount of N. gonorrhoeae on the pharyngeal surface. With daily use it may increase gonococcal clearance and have important implications for prevention strategies,” the researchers conclude.
The findings, published on 20 December 2016 in Sexually Transmitted Infections
, reinforce claims made as long ago as 1879 by the manufacturer of Listerine that the product had the potential to cure gonorrhoea.
Researchers added a sample of N. gonorrhoeae to a series of dilutions (up to 1:32) of Listerine Cool Mint and Listerine Total Care. A saline solution was used as a control. The number of N. gonorrhoeae colonies were measured in the samples.
The researchers found that Listerine dilutions of up to 1:4 in contact with N. gonorrhoeae for a minute led to significant reductions in the total number of colonies. There was no inhibitory effect in the saline control.
In a clinical trial, 196 men who attended a sexual health clinic in Melbourne who had pharyngeal gonorrhoea were recruited. Some 58 (30%) had tested positive for N. gonorrhoeae before the trial.
Untreated men were requested to either rinse or gargle for a minute with a Listerine solution or a saline solution. Pharyngeal swabs were taken before and after to test for N. gonorrhoeae.
The researchers found that men in the Listerine group were less likely to have a positive culture test result for N. gonorrhoeae on the pharyngeal surface (52%) compared with men in the saline group (84%); P=0.013.
 Chow EPF, Howden BP, Walker S et al. Antiseptic mouthwash against pharyngeal Neisseria gonorrhoeae: a randomised controlled trial and an in vitro study. Sexually Transmitted Infection 2016. doi: 10.1136/sextrans-2016- 052753