Syphilis, chlamydia and gonorrhea are three of the most common sexually transmitted infections (STI). Over the last decade, these STIs have seen a resurgence in many parts of Canada, with most infections seen in major urban centres. These infections have primarily affected gay, bisexual, and other men who have sex with men (gbMSM). Recently, a small pilot study found that doxycycline — an inexpensive, well-tolerated antibiotic — given daily may prevent new STIs in gbMSM. Another study looked at the use of doxycycline given after a sexual encounter for prevention of STIs, and the results of this study showed protection against STIs as well. Based on these promising data, along with the concerning increases in STIs seen in Canada, the current study will examine the use of doxycycline as either a daily prevention therapy (preexposure prophylaxis, or PrEP) or an ‘after sex’ prevention tool (postexposure prophylaxis, or PEP) for STIs in gbMSM. While examining for efficacy as its primary goal, this study will also do an examination of some of the potential challenges and concerns associated with the use of a daily antibiotic: drug resistance, tolerability and side effects, and how acceptable this drug is for people to take regularly.