Sexual health experts are urging caution when prescribing doxycycline as a morning after pill for STI prevention in gay, bisexual and other men who have sex with men until the true impact on antimicrobial resistance is understood.

While the use of doxycycline post-exposure prophylaxis (doxy-PEP) was “unavoidable”, they said its widespread implementation without adequate surveillance “warrants increased vigilance”.

The team, including Associate Professor Catriona Bradshaw from the Melbourne Sexual Health Research Centre, wrote in the Medical Journal of Australia in response to a consensus statement published last September.

The guidance suggested that doxy-PEP — taken as a single 200mg dose within 72 hours of condomless sex — “should be considered” primarily for syphilis prevention in high-risk men who have sex with men (MSM).