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How Effective is PrEP?

How Effective is PrEP?

Updated on:
September 2, 2021

Are you sexually active and want to minimize your exposure to HIV? Today, we have more tools than ever to prevent HIV and reduce harms associated with having an active sex life.

Pre-exposure prophylaxis (PrEP) works to prevent HIV infection in those who are HIV negative and at higher risk for HIV. PrEP combines two drugs in one pill that is taken every day.

When PrEP is in your bloodstream, it can stop HIV from taking hold and spreading, keeping you HIV negative.

PrEP Effectiveness

PrEP is highly effective in preventing HIV. When PrEP is taken as daily prescribed, it reduces the risk of getting HIV by 99%. PrEP is even more effective when combined with other protections, such as condoms. Though it can also be prescribed as PrEP on demand.

You should consider taking PrEP if:

  • You have sexual intercourse with multiple partners
  • You inject drugs and/or use drugs during sex
  • You had condomless sex without knowing your partner's HIV status

When taken as prescribed, PrEP is safe and effective. However, PrEP may cause minor side effects such as nausea, diarrhea, fatigue, headache, and stomach pain for a small number of patients in their first days of PrEP.

PrEP effectiveness for bottoming

PrEP is one of the best options for receptive anal sex. When taken daily for seven days, PrEP is extremely effective in preventing HIV. As explained above, it's okay to miss a few doses, however, if you find that sticking to daily PrEP is challenging, speak to your healthcare provider for some strategies that can help. For example, prescribing PEP could make more sense in emergency situations.

Be aware that each dose you miss reduces the effectiveness of PrEP. It's best to follow a daily dosage schedule if you want maximum protection.

PrEP effectiveness for topping

Insertive partners have a statistically lower chance of getting HIV. However, this doesn't mean that you're risk-free. In deciding whether to take PrEP as a top, there are some things to consider.

How long does PrEP take to be effective?

PrEP is not immediately effective. Like any other medication, it takes time for it to take effect. When it comes to anal sex, PrEP is highly effective after taking it for seven days without missing a dose. For vaginal / frontal sex, it takes PrEP about 21 days to reach desired concentrations.

What causes PrEP to not be effective?

Research has found that PrEP is less effective when it isn't taken every day. This lack of protection is because there isn't enough of the medicine in your body to prevent HIV from spreading.

If PrEP is taken four times a week, it's 99% effective at preventing HIV infection through anal sex. If taken only two times a week, effectiveness drops to 75%.

As PrEP's efficiency decreases when doses are missed, adherence (taking your medication as prescribed) is essential to maintain maximum levels of protection.

Is your partner HIV negative? Are they correctly taking PrEP? Do you want total control over preventing HIV, or are you willing to accept the small risk of getting HIV as a top? Are you using a condom correctly each time you have sexual intercourse?

These are all questions to think about before deciding whether to take PrEP.

Reviewed by:
Thomas Trombetta

Thomas is passionate about gender and sexuality liberation social movements. Before beginning his work with Freddie, Thomas studied Sociology and Global & Development Studies at the University of Alberta, after which he began working with marginalized communities. In previous roles, Thomas was involved in queer and trans health education, PrEP health promotion, community-based research, HIV education, and LGBTQ2S+ advocacy.