As the mandelic acid salt (methenamine mandelate) or the hippuric acid salt (methenamine hippurate), it is used for the treatment of urinary tract infections. In an acidic environment, methenamine is believed to act as an antimicrobial by converting to formaldehyde. A systematic review of its use for this purpose in adult women found there was insufficient evidence of benefit and further research was needed. A UK study showed that methenamine is as effective as daily low-dose antibiotics at preventing UTIs among women who experience recurrent UTIs. As methenamine is an antiseptic, it may avoid the issue of antibiotic resistance.
Methenamine acts as an over-the-counter antiperspirant due to the astringent property of formaldehyde. Specifically, methenamine is used to minimize perspiration in the sockets of prosthetic devices.