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Fact Sheet

Pre-Exposure Prophylaxis (PrEP)


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What Are Some of the Safety Concerns Associated With PrEP?

Drug Resistance

A person could develop drug resistance if they are HIV-positive (and don't know it) when starting PrEP or they become HIV-positive while taking PrEP. Once a person's HIV becomes resistant to the PrEP drugs, those same anti-HIV drugs may not work for treating their HIV.

A person who uses PrEP needs to follow the medication schedule that their doctor recommends. If the schedule is not followed -- if a person misses too many doses or experiments with another schedule -- then the risk of becoming infected and developing drug resistance can increase.

Side Effects

Anti-HIV drugs cause side effects, which may negatively affect a person's quality of life and ability to adhere to their medication schedule. Although the drugs selected for PrEP studies are generally better tolerated than other drugs used to treat HIV, they are still capable of causing mild to severe side effects. Some of the possible side effects include nausea, vomiting, diarrhea, headache and dizziness. PrEP may also cause decreases in kidney function and bone density. However, research suggests that side effects while using PrEP are generally mild and uncommon.

A False Sense of Security

Another concern is that people may feel a false sense of security when using PrEP and decide to engage in more risky activities. If people using PrEP decide to have sex with more partners, use condoms less often or share needles more frequently, then their overall risk for HIV infection (and other STIs) may increase because PrEP does not provide complete protection.


Now That Studies Have Found That PrEP Can Reduce the Risk of HIV Infection, Where and When Will People Be Able to Get It?

The anti-HIV drugs used for PrEP must be prescribed by a doctor, who can provide them in a safe and informed way. However, it is difficult to predict if and when PrEP will be widely available from doctors. Currently, no forms of PrEP have been approved by Health Canada.

Although anti-HIV drugs have not been approved for the prevention of HIV (as PrEP), they have been approved for the treatment of HIV. Once a drug has been approved, it can be prescribed by doctors for other conditions. This practice is called "off-label" use of prescription drugs. Some forms of PrEP, such as oral Truvada pills, can be prescribed by doctors in this way.

Because of the high cost of anti-HIV drugs, advocacy may be needed to get PrEP covered by provincial and territorial drug programs and ensure that people who need PrEP can access it. Some private health insurance plans may cover the cost of the drugs.

Obtaining anti-HIV drugs from other sources -- from a friend, people at parties, or over the internet -- may be dangerous. Anti-HIV drugs obtained from these sources may be fake, of poor quality or contain a different medication than expected.

Not all anti-HIV drugs and medication schedules may be appropriate for PrEP. Currently, only two anti-HIV drugs (there are more than 25 available) are known to be effective as PrEP and only if they are taken every day. Obtaining PrEP from a doctor will help ensure that a person is prescribed the right medications at a safe dose and provided with accurate information on how to use them safely and effectively. Incorrect use of anti-HIV drugs can cause serious, even life-threatening, reactions in some people. These drugs can also interact with other prescription drugs, recreational drugs and other substances. These interactions can be harmful, even when there are no symptoms. In rare cases, when not taken correctly, anti-HIV drugs have caused fatal overdoses.

Regular testing and medical check-ups are needed to ensure that a person remains healthy while using PrEP. To avoid drug resistance, regular HIV testing is needed to ensure that a person is HIV-negative before starting PrEP and that they remain HIV-negative while using it. If a person becomes HIV-positive, they will need to stop using PrEP.


Abdool Karim Q, Abdool Karim SS, Frohlich JA et al. Effectiveness and safety of tenofovir gel, an antiretroviral microbicide, for the prevention of HIV infection in women. Science. 2010 Sep 3;329(5996):1168-74.

Baeten JM, Donnell D, Ndase P et al. Antiretroviral prophylaxis for HIV prevention in heterosexual men and women. New England Journal of Medicine. 2012 Aug 2;367(5):399-410.

Grant RM, Lama JR, Anderson PL et al. Preexposure Chemoprophylaxis for HIV Prevention in Men Who Have Sex with Men. New England Journal of Medicine. 2010 Nov 23 [cited 2010 Dec 13];(Epub ahead of print).

Thigpen MC, Kebaabetswe PM, Paxton LA et al. Antiretroviral preexposure prophylaxis for heterosexual HIV transmission in Botswana. New England Journal of Medicine. 2012 Aug 2;367(5):423-34.

Van Damme L, Corneli A, Ahmed K et al. Preexposure prophylaxis for HIV infection among African women. New England Journal of Medicine. 2012 Aug 2;367(5):411-22.

Marrazzo J, Ramjee G, Nair G et al. Pre-exposure Prophylaxis for HIV in Women: Daily Oral Tenofovir, Oral Tenofovir/Emtricitabine, or Vaginal Tenofovir Gel in the VOICE Study (MTN 003). 20th Conference on Retroviruses and Opportunistic Infections, Atlanta, Paper#26LB, 2012.

Choopanya K, Martin M, Suntharasamai P, Sangkum U, Mock PA, Leethochawalit M, et al. Antiretroviral prophylaxis for HIV infection in injecting drug users in Bangkok, Thailand (the Bangkok Tenofovir Study): a randomised, double-blind, placebo-controlled phase 3 trial. The Lancet. 2013 Jun;381(9883):2083-90.

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This article was provided by Canadian AIDS Treatment Information Exchange. Visit CATIE's Web site to find out more about their activities, publications and services.
See Also
More on HIV Medications for HIV Prevention

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