HIV Prevention

What is pre-exposure prophylaxis?

Pre-exposure prophylaxis (PrEP) refers to HIV medicine taken by people without HIV to reduce the risk of HIV transmission before a possible exposure. The word “prophylaxis” means to prevent or control the spread of an infection or disease.

Four HIV medicines are approved by the U.S. Food and Drug Administration (FDA) for use as PrEP: 

• Descovy (or a generic equivalent), a pill taken by mouth every day.
• Truvada (or a generic equivalent), a pill taken by mouth every day.
• Apretude, a shot taken every two months.
• Yeztugo, a shot taken every six months.

Which medicine to use for PrEP depends on a person’s individual situation.

PrEP works by blocking the HIV life cycle. This prevents the virus from taking hold and spreading if exposed during sex or injection drug use. However, its effectiveness relies on taking the medication as prescribed to ensure there is enough medicine in the bloodstream to stop the virus from spreading.

Should I consider taking PrEP?

PrEP is used by people who do not have HIV and who may be exposed to HIV through sex or injection drug use. PrEP is not intended for people with HIV or who have recently been exposed to HIV.

According to the Centers for Disease Control and Prevention (CDC), PrEP may be beneficial if you do not have HIV and—

• You have had anal or vaginal sex in the past six months and—
  • Have a sexual partner with HIV (especially if the partner has an unknown or detectable viral load),
  • Have not consistently used a condom, or
  • Had a sexually transmitted infection (STI) in the past six months
• You inject drugs and—
  • Have an injection partner with HIV, or
  • Share needles, syringes, or other injection equipment
• Have been prescribed post-exposure prophylaxis (PEP) and—
  • Report continued sex, or
  • Have used multiple courses of PEP

If you think PrEP may be right for you, talk to your health care provider. PrEP can only be prescribed by a provider, and you’ll need to take other tests to make sure it’s safe and appropriate for you.

How well does PrEP work?

According to the CDC, PrEP pills and shots can reduce the risk of sexual HIV transmission by about 99% when taken exactly as prescribed. PrEP pills can reduce the risk of HIV transmission from drug injections by as much as 74%. PrEP shots have not been studied for this type of HIV exposure. It is important to avoid sharing needles, syringes, or other injection equipment even while taking PrEP.

Although getting HIV is unlikely when taking PrEP as prescribed, it can still occur. In rare cases, people who get HIV while taking PrEP may develop HIV drug resistance. People who develop drug resistance may have fewer treatment options. However, a health care provider can still help identify effective options. Taking PrEP exactly as prescribed remains one of the safest and most effective ways to prevent HIV.

PrEP does not protect against other STIs. Combining other prevention methods (such as condom use) with PrEP can further reduce the risk of HIV or other STIs.

Does PrEP cause side effects?

Some people taking PrEP may experience side effects such as nausea, diarrhea, headache, dizziness, and insomnia. These side effects are typically mild and go away over time. In rare cases, more serious side effects such as kidney failure and lactic acidosis can occur.

Before starting PrEP, consult with your health care provider about any potential side effects. If you are taking PrEP, tell your health care provider immediately if you have any side effects that make it difficult to keep taking your PrEP medicines.

How often should you take PrEP?

PrEP pills: PrEP pills (Truvada or Descovy) should be taken once a day. This is the only CDC- and Food and Drug Administration (FDA)-recommended way to take PrEP pills for HIV prevention.

Some people may take PrEP “on demand” only when they have a high chance of HIV exposure. On-demand PrEP refers to a “2-1-1” schedule, in which you take two PrEP pills between two and 24 hours before sex, one pill 24 hours after the first dose, and another pill 24 hours after the second dose. 

Because on-demand PrEP is not recommended by CDC or approved by FDA, this approach should only be considered if recommended by your health care provider. 

PrEP shots: PrEP shots should be received every two months (Apretude) or every six months (Yeztugo). Depending on the type of shot, you may also be required to have more frequent shots or take pills for a couple of days when you first start injectable PrEP.

Whether taking PrEP pills or shots, it is important to take all doses on time. PrEP is much less effective when it is not taken as prescribed, which increases the likelihood of HIV transmission and drug resistance.

What else should you know about PrEP?

People taking PrEP should be tested for HIV regularly (usually every three months), which may require routine follow-up visits with a health care provider. If taking PrEP as scheduled doesn’t work for you or if you want to stop taking PrEP altogether, talk to your health care provider first before making changes.

You are unlikely to get HIV if you take PrEP as prescribed. If you do get HIV while taking PrEP, you will need different medicines for treatment. For information on what to do if you test positive for HIV, see the HIVinfo fact sheet Just Diagnosed: Next Steps After Testing Positive for HIV.

This fact sheet is based on information from the following sources:

From CDC:

• Clinical Guidance for PrEP
• Let’s Stop HIV Together: PrEP
• Preventing HIV with PrEP
• PrEP Medication Guide: Reduce Your Risk of Getting HIV
• Now’s the Time to Find Out About PrEP and PEP

From DailyMed:

• Truvada
• Descovy
• Apretude
• Yeztugo

Also see the HIV Source collection of HIV links and resources.