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How effective is PrEP?

Dr. Demetre: This is a great question. People throw a lot of numbers out. How effective is PrEP, what’s the real deal?

Dr. David: Got questions about PrEP? #AskTheHIVDoc has all the answers.

Dr. Demetre: Well, the answer is if you take PrEP the medicine is effective. But it’s only as effective as you make it. Which means you have to take it everyday. The medicine is effective but it’s not effective if it sits on your shelf, in the bottle or in the pharmacy. That’s like every other drug in the world. If you take your high blood pressure medicine, it makes your blood pressure better. If you take your medicine that prevents HIV infection, it prevents HIV.

When taken as prescribed, PrEP – the HIV prevention pill – is highly effective! If you’re exposed to HIV while taking PrEP, the medicine can block HIV from taking hold in the body. In a major study of gay and bi men, as well as trans women, daily PrEP use lowered their risk of getting HIV by an estimated 99 percent – that’s pretty amazing!

If you decide to start PrEP, remember that it will take some time for the pill to reach maximum effectiveness – at least seven days for men who have sex with men, and longer if you are a woman having vaginal sex.

Find out if PrEP is right for you. Click here to find a PrEP-friendly provider near you. 



#AskTheHIVDoc is a video series from Greater Than HIV featuring top HIV doctors providing answers to commonly-asked questions about HIV prevention, testing and treatment.

This information is shared for educational purposes only and should not be used as a substitute for professional medical advice. The views expressed are those of the featured medical professional and reflect information available to that professional at time of filming. Always consult a health care provider for any personal health decision.

While we make every effort to keep the medical information on our website updated, we cannot guarantee that the information reflects the most up-to-date research. Also, please note the views expressed by individuals who appear in Greater Than HIV videos and other content are their own and are not made on behalf of any groups/organizations/associations.