What is PrEP?

PrEP is a medication that is used as an HIV prevention strategy by those of us who are HIV-negative.

PrEP comes in the form of a single pill that contains two medications. When taken regularly, and with the support of a medical care provider, PrEP greatly reduces the chances of picking up HIV (becoming HIV positive).

PrEP stands for Pre-Exposure Prophylaxis. Basically, prophylaxis is a treatment or tool designed to prevent disease or infection, and PrEP is a medication taken specifically to prevent HIV.

PrEP is sometimes known as its brand name Truvada  (emtricitabine/tenofovir).


How PrEP works...

While PrEP as a prevention strategy is relatively new, the pill that we take as PrEP has been used by those of us living with HIV as treatment since 2004.

PrEP prevents HIV by stopping HIV from establishing itself in our bodies. This stops us from becoming HIV positive. HIV transmission can be prevented once the medications in PrEP reach therapeutic levels in our bodies. It is important that we take PrEP as it is prescribed so we maintain the concentration of PrEP in our bodies needed to prevent HIV.

The health care professionals who prescribe PrEP will share more information about how to take PrEP, and how PrEP works.


Ways to take PrEP...

There are two ways to take PrEP that we will discuss in this section. The method recommended by Health Canada is taking PrEP every day (Daily PrEP). Another method is taking PrEP on-demand, which basically means taking PrEP when we are planning to have the kinds of sex that can pass HIV to another person. In this resource, we provide information about both ways of taking PrEP to make sure that community members interested in PrEP know that there are options.

It’s important to start with a discussion with a doctor or nurse practitioner about the sex that we have, the sex we want to have, and our preferred way of taking PrEP and other medications.


Current Health Canada guidelines recommend taking PrEP every day. Taking PrEP every day helps us make sure that we maintain the concentration of PrEP needed to prevent HIV. This is the way most people take PrEP. Because we can’t always predict when sex is going to happen, maintaining a regular dose of PrEP is a great way to stay consistently covered.


Research has demonstrated that “on-demand” or “event-based” use of PrEP is also effective in preventing HIV transmission during anal sex.

On-demand PrEP may make sense for guys who have sex less than once per week, and for guys who plan out when they are having certain kinds of sex.  More information on on-demand use of PrEP can be found in the “How effective is PrEP?” section of this website.


PrEP and other STIs...

It is important to remember that PrEP only prevents HIV and does not prevent the transmission of any other STIs (Sexually transmitted infections). Condom use is still the most effective prevention method for many different kinds of STIs. Most STIs are treatable with medication, and so regular testing helps us and our partners know what our sexual health status is and access treatment if necessary. When we take care of our sexual health with PrEP, condoms, and regular testing we help ourselves, our partners, and our community by preventing the spread of STIs and HIV.


For those of us taking testosterone...

There is not a lot of clinical data on how hormone therapy (e.g. testosterone taken by trans guys) interacts with PrEP. However, we do know that there have been no reported negative interactions between testosterone and the medications in PrEP (which is also sometime used to treat HIV).

There may be other considerations for front hole sex when someone is on testosterone. Some people on testosterone experience genital atrophy (thinning of the tissue inside the front hole). This makes the tissue more vulnerable to small tears during receptive sex.   We don’t have conclusive data on the effectiveness or dosing requirements of PrEP for front hole sex when someone has thinner genital tissue. While it is still considered to be highly effective, you may want to bring this up with the person prescribing you PrEP because small tears can increase the chances of getting an STI, including HIV.

To make sure we have the most up-to-date information, It’s important that we try and inform our PrEP prescriber about any hormone or other therapy or medication we may be on.


For those of us having frontal and/or anal sex...

Bodies are diverse. Some bodies have a penis and an anus that can be used for sex, some bodies have a front-hole (sometimes called a vagina) and an anus that can be used for sex. The kind of body, and body parts that we have changes the ways that we might need to take PrEP.

It is necessary to have been on PrEP for seven days for it to be fully effective at preventing HIV. If we are having receptive frontal/vaginal sex, almost perfect adherence is required, meaning taking PrEP daily with very few missed doses. The tissues in the front-hole are different than the tissues in the ass which means that we may need to be more diligent about taking PrEP daily to make sure we are covered.

In addition to this, those of us having front-hole sex need to make sure that we take PrEP every day, missing a few doses as possible. This means that on-demand PrEP is not effective when it comes to front hole sex.

While PrEP has generally shown to work well at preventing HIV, research is ongoing and studies are being conducted with trans guys to determine specific guidelines that address how PrEP interacts with our bodies.