Antiretroviral (ARV) therapy not only helps people living with HIV. It also plays a role in preventing transmission of the virus.

Post-exposure prophylaxis (PEP): PEP involves taking a short course of ARV drugs, usually for a month, after a high-risk exposure. To be most effective, PEP should be started immediately after possible exposure, waiting no more than 72 hours.

If you suspect a high-risk exposure to HIV—semen leaking out of a condom during intercourse with an HIV-positive insertive partner; receptive anal sex without a condom with a partner who is either HIV positive or whose status you do not know or you have shared drug-injection works with someone who is either HIV positive or whose status you do not know—contact your health care provider or local hospital emergency room as soon as possible.

Pre-exposure prophylaxis (PrEP): PrEP is an HIV prevention tool in which an HIV-negative person takes antiretroviral medication to reduce the risk of contracting HIV. Currently, the available form of PrEP entails taking the pill Truvada, which is made of two drugs—tenofovir and emtricitabine. When these meds build up in the human body, they can stop HIV from replicating and establishing an infection. PrEP was approved in 2012 by the U.S. Food and Drug Administration (FDA) with the requirement that it be used every day, even during periods of minimal or low-risk sexual activity. Future studies are exploring intermittent dosing strategies (for example, using PrEP only during high-risk periods). Researchers are also looking into injectable, long-lasting forms of PrEP as well as different medications that could be used as PrEP.

The Centers for Disease Control and Prevention (CDC) recommends Truvada for those at high risk of HIV, including:

  • Those in a relationship with an HIV-positive partner.
  • Men who don’t use condoms when having sex with men.
  • Men who have been diagnosed with a sexually transmitted infection (STI) in the past six months and who are not in a mutually monogamous relationship with an HIV-negative partner.
  • Heterosexuals who don’t always use condoms for sex with partners who are themselves at high risk for HIV.
  • Anyone who, in the past six months, has shared equipment when injecting illicit drugs or who has been in an injection drug treatment program.

According to CDC recommendations, before prescribing PrEP, health care providers should thoroughly assess a patient’s HIV risk behaviors and also administer an HIV test. (More sensitive HIV tests can detect a more recent, or acute, infection; however, most home tests will not detect HIV during this “window period.”) Tests for STIs are recommended. So, too, are tests for kidney function—tenofovir is associated with kidney toxicity—and hepatitis B virus (HBV), given that Truvada is also active against HBV and must be used cautiously.

It is recommended that providers prescribe no more than a 90-day supply of PrEP and to offer extensive HIV risk-reduction counseling, adherence counseling and condoms. It is recommended that, before renewing Truvada scripts, providers follow up with patients every two to three months to test again for HIV, to assess adherence and HIV risk behavior, and to provide ongoing support and counseling. Kidney function testing is again recommended three months after a person first starts PrEP and yearly thereafter. Tests for common STIs are also recommended every six months, even if a person has no symptoms.

PrEP is appropriate for periods of time when people have greater risk for contracting HIV. Those periods may be short, long or recurrent, depending on the individual. The CDC also recommends that before people discontinue PrEP—whether because of safety concerns, a positive HIV test result, or a person requests to stop treatment—their providers should link them to HIV care (if a person has become infected) or ongoing HIV risk-reduction counseling and support. For people who have hep B, their providers should also discuss whether to continue treatment as a means to control their hepatitis.

How does PrEP work?
PrEP only works if you take it. Data from the iPrEx trial show that daily adherence reduces HIV risk between 96 percent and greater than 99 percent. Those who took four doses a week remained fully protected, and those who took two lowered their chance of getting HIV by 76 percent.

What about side effects?
Rates of side effects while on PrEP are low. Mild symptoms such as stomach cramps, headaches and loss of appetite may appear the first few weeks. Long-term use raises issues of kidney health and bone density. Health care providers should regularly test for kidney function.

What about drug resistance?
If you are HIV positive and start PrEP, the virus can become resistant to one or both meds in Truvada. This mutated virus is weaker and less likely to transmit. Still, it is important you are not in the window period of HIV infection when beginning PrEP.

Do I still need to use condoms?
PrEP is supposed to be used along with safer-sex practices, such as condom use and regular HIV testing.

How can I access PrEP?
At over $1,000 a month, PrEP is not cheap. Most insurance plans cover it, but you may have to work with your health care team before you get a prescription and coverage.

Last Revised: February 14, 2016