Research consistently shows PrEP, when taken daily as prescribed, significantly reduces the likelihood of acquiring HIV for cisgender men, and women who are transgender or cisgender. However, research has not yet determined if PrEP works for transgender men. PrEP research has focused on cisgender gay men and other men who have sex with men, as well as cisgender men and self-identified women who are heterosexual and/or use injection drugs.

So far, research has only been done with people over the age of 18, so we do not know how PrEP works for younger youth. The level of risk reduction that PrEP provides varies greatly based on a person’s exposure to HIV and how closely individuals follow the prescription. If we are using PrEP, it is important to follow our doctor's instructions about how to use it. 

Studies have shown that PrEP reduces the risk of HIV acquisition between 74% and 92% among individuals who take Truvada daily as prescribed. In these studies, research participants were also given access to safer sex counselling, STI testing and treatment, and condoms. The research participants reported a range of sexual acts and relationships, including having multiple partners, anal sex, and vaginal sex. PrEP does not prevent other STIs such as chlamydia, gonorrhea or syphilis.

PrEP can be used alongside existing HIV prevention methods such as using condoms. We also know that PrEP alone significantly reduces the possibility of becoming HIV-positive, when taken daily as prescribed. PrEP does not work immediately when we start taking it: current evidence suggests it can take between 7 and 21 days for there to be enough medication in our bodies to prevent HIV.

More research is underway in Canada and globally to learn more about PrEP.  Current research is looking at the long-term impacts of using PrEP, and if PrEP still works if taken less often or in other forms, such as injections. At this point, Truvada is the only medication that has been approved for use as HIV PrEP in Canada. Because of the impacts PrEP can have on our bodies, it is important to be monitored regularly by a doctor when taking PrEP.