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Sexual and Reproductive Health

HIV Pre-Exposure Prophylaxis (PrEP)

​​​​​​​​​​​Human immunodeficiency virus (HIV) attacks the immune system and makes it hard for the body to fight diseases and infections. HIV is passed (transmitted) through blood, semen, and fluids from the vagina and rectum.

HIV pre-exposure prophylaxis (PrEP) helps prevent HIV in people who have a very high risk of getting the virus. It is taken as a pill once a day.

Who should think about taking HIV PrEP?

You should think about taking HIV PrEP if you are HIV-negative and have a high, ongoing risk of getting HIV. This includes men who have sex with men (MSM), transgender women, people who have anal sex without a condom in the past 6 months and people who:

  • have had chlamydia, gonorrhea, or syphilis in the past 12 months
  • have a sex partner with HIV who is not getting treatment or doesn’t know their HIV virus levels
  • have many sex partners
  • inject drugs and share needles or other drug equipment
  • have sex partners that belong to populations with high rates of HIV (such as MSM and people from countries or areas where HIV is common)

Who doesn’t need to think about HIV PrEP when you have a partner living with HIV?

If you are in a stable, closed relationship with a partner living with HIV who is getting treatment and has very low levels of HIV in their blood, you don’t need to think about taking HIV PrEP.

People with very low levels of HIV in their blood have an undetectable viral load. This means that standard tests don’t detect that they have HIV. If your partner has an undetectable viral load, they won’t pass HIV to you. This is called U=U which means HIV that is undetectable is untransmissible and can’t be passed from one person to another.

How well does HIV PrEP work?

HIV PrEP lowers the risk of getting HIV from sexual activity by more than 95% when it’s taken every day. It uses tenofovir disoproxil fumarate (TDF) and emtricitabine (FTC) (a combination of medicines that is also called TDF/FTC or Truvada) and are the same medicines used to treat HIV. HIV PrEP stops the virus from making copies of itself (multiplying).

The medicine doesn’t work right away to protect you so it’s important to use condoms or avoid having sex for at least:

  • 7 days, if you have anal sex
  • 20 days, if you have vaginal sex

HIV PrEP works best to help lower your risk of getting HIV when you also talk openly with your sex partners about their HIV status, use condoms, and have regular STI testing.

How do I start HIV PrEP?

Talk to your healthcare provider if you want to start taking HIV PrEP. They will need to look at your vaccine history and send you for tests that check for HIV and other sexually transmitted infections (STI), liver infections (called hepatitis), pregnancy (if needed) and tests to see how well your kidneys are working. Once your healthcare provider has all of your information, they will be able to decide if they can give you a prescription for HIV PrEP.

What do I need to know about taking HIV PrEP?

When you take HIV PrEP, you will need to have regular appointments with your healthcare provider. You will also need to have blood tests and STI testing about 30 days after starting HIV PrEP and every 3 months while you take it. You can take HIV PrEP:

  • any time of day, with food or without food
  • with hormones, including birth control and hormone replacement therapy
  • with alcohol (Since alcohol can make it harder to remember things, think about setting a phone alarm to remind you to take your medicine.)

What are the side effects of HIV PrEP?

The most common side effects of HIV PrEP include:

  • headache
  • stomach pain
  • weight loss
  • upset stomach (nausea) or vomiting
  • gas (flatulence)
  • loose stool (diarrhea)
  • dizziness

Most of these side effects are mild and get better in a few weeks. If side effects bother you, change the time of day you take your medicine or try taking it with food.

In rare cases, HIV PrEP may cause damage to bone or kidneys. This damage tends to be mild and will get better after you stop HIV PrEP.

What else do I need to know?

HIV PrEP doesn’t prevent other STIs. It’s important to have regular STI testing and go for testing right away if you have symptoms of an STI, such as discharge from the penis or vagina or burning when you pee (urinate).

If you have HIV and you take HIV PrEP before you have been diagnosed, you may develop drug resistance to TDF and FTC. This may prevent these drugs from working to treat HIV and limit your treatment options.

If you want to stop taking HIV PrEP, wait 28 days after your last contact with someone who has or who may have HIV. You should have HIV testing between 4 and 8 weeks after stopping it.

HIV PrEP doesn’t prevent pregnancy so talk to your healthcare provider about birth control options.

Where can I get more information?

For more information about sexual health, call Health Link at 811 or visit:

Current as of: October 15, 2020

Author: Provincial STI Program, Communicable Disease Control AHS