PrEP (pre-exposure prophylaxis) is a preventative antiviral medication that if taken appropriately reduces your chances of getting HIV if you are exposed. It is available either as an oral medication or as an injection. When PrEP is taken as prescribed, it is a highly effective way of preventing HIV transmission (99% effective for exposures through sex, and at least 74% effective for exposures through injection drug use).

PrEP can cause some people to experience side effects including nausea, diarrhea, headaches, fatigue, and stomach pain. Typically these side effects go away within a few days.

There are no known interactions between PrEP and alcohol or any recreational drugs.

It is safe and effective to take both PrEP and birth control or emergency contraception.

It is safe and effective to be on both PrEP and HRT.

PrEP is only effective for preventing HIV. It does not prevent other STIs. When taking PrEP and having condomless sex, it is good practice to see a provider quarterly for routine STI screening, since many STI are asymptomatic.

If taken as prescribed, PrEP is highly effective at protecting you from HIV during condomless sex. However, PrEP does not protect you from other kinds of STIs or prevent pregnancy. Whether it makes sense to stop using condoms or other barriers depends on your specific situation, and whether might be at risk of other STIs or unwanted pregnancy.

Most insurance plans and state Medicaid plans cover PrEP. Co-payments and deductibles may vary state by state, but many clinics and the companies that make PrEP have programs to subsidize those costs of PrEP for those with more limited means. If you are uninsured, there are other programs available to help pay for PrEP. Look at this flowchart and this list of PrEP financial assistance programs.

You will need HIV testing every three months while you are on PrEP. Even though it’s very unlikely that you will get HIV if you are taking PrEP as prescribed, it’s important to test regularly because taking PrEP medication if you become HIV positive can result in drug resistance to the antiretroviral medications used to treat HIV.

If it is difficult for you to see your healthcare provider regularly, there are many online options for HIV testing. There are also a number of telehealth services available online that prescribe oral PrEP. For more information, see our resource list.  

Some people use on-demand PrEP instead of daily PrEP. This means that they take 2 pills 2 to 24 hours before a possible HIV exposure, 1 pill 24 hours after the first dose, and 1 pill 24 hours after the second dose.

The 2-1-1 method has only been tested in cisgender men using PrEP to prevent HIV transmission during anal sex. At this point, it’s not possible to definitively say whether it’s effective in other groups of people, including transmasculine people, or for different types of exposures, such as vaginal sex or sharing injection supplies.  

The primary concern is that PrEP may take longer to be fully effective in cervical and vaginal tissues than rectal tissue. Some analyses of daily PrEP suggest that rectal tissues, cervical and vaginal tissues have different pharmacology in regards how quickly the medicine (tenofovir) gets into each tissue type. Missed doses of medication may be less problematic for people whose only exposure to HIV is through anal sex, because of tenofovir’s rapid uptake in anal cells, compared to cervical and vaginal cells. That means that when you use a method that involves taking fewer doses, or if you miss doses, you may be less protected from HIV during frontal/vaginal exposures than anal exposures.  

Since we know that daily oral PrEP and injectable PrEP are effective for transmasculine people, those are the most reliable options until we have more information.

Truvada^TM (tenofovir disoproxil fumarate and emtricitabine) has been approved for people of all genders, so Truvada is a safe and reliable choice no matter what types of sex or HIV exposures you have.

Descovy^TM (tenofovir alafenarmide and emtricitabine) is currently only approved for cisgender men and transfeminine people because there hasn’t been adequate research evaluating whether it’s effective for cisgender women or transmasculine people. There is currently an ongoing study of Descovy^TM in cisgender women, so we should have more information in the future. Dr. Kenneth Mayer suggests that Descovy^TM is most likely an effective option if your only HIV exposure is through anal sex, but if there is any potential for an HIV exposure through frontal /vaginal sex, Descovy^TM is not yet known to be effective and may not be the best option available for you.  

If it has been less than 12 hours when you realize you missed a dose of PrEP, take your missed dose right away. Past 12 hours, wait until it is time to take your next dose as usual.  

PrEP is less effective when you miss doses (much like birth control). If you miss just one pill very occasionally, you should still have a high level of protection. If you’ve missed more doses, let your healthcare provider know, and consider using another form of protection from HIV (such as condoms) until you’ve reached maximum protection again. Data suggests that 4 or more pills a week still has a high level of protection for anal sex, while anything less than 6 a week is significantly less protection for frontal/vaginal sex.

There is currently one kind of injectable PrEP available, which is called Apretude (cabotegravir)^TM. It is an intramuscular injection, which your healthcare provider will administer every two months after an initial loading dose.  

Injectable PrEP is approved for anyone who needs protection from HIV during sex. However, injectable PrEP is currently not recommended for people who need protection from HIV during injection drug use or while sharing injection supplies.

There are various options when it comes to PrEP forms. Here is a quick flowchart that can guide your decision-making process when it comes to which PrEP works for you.

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What we do know:

• For receptive anal sex, you will have maximum protection after 7 days of daily oral PrEP.

• For receptive frontal/vaginal sex, the CDC says you will have maximum protection after 21 days of daily oral PrEP.

• For injection drug use, the CDC says you will have maximum protection after 21 days of daily oral PrEP.

What we don’t know:

• When insertive partner will have maximum protection during anal or frontal/vaginal sex

• When you will have maximum protection from injectable PrEP

Dr. Kenneth Mayer suggests that although the time to optimal protection from injectable PrEP is not well understood, if you decide to start injectable PrEP, it makes sense to follow the guidelines for when you would be protected by daily oral PrEP for the best possible estimate.

For more information on how long it takes to have maximum protection from PrEP, read these guidelines from the CDC.

PrEP is effective for preventing HIV when taken before an exposure. If you have already had an exposure, PEP (post-exposure prophylaxis) may be a good option. See the next question below for more information about PEP.

PEP (post-exposure prophylaxis) is a medication you can take after an HIV exposure to prevent HIV infection. You have to start PEP within 72 hours of exposure, and it is more effective the sooner you start to take it. After you start PEP, you will need to take it daily for 28 days. PEP is available in the emergency room in a crisis, but it’s also possible to get it from an urgent care, your primary care, or a sexual health clinic.

It is possible to transition directly from PEP to PrEP! You do not need to take a break between the two. If you think it’s likely that you’ll have another HIV exposure, it’s better to avoid a gap between PEP and PrEP. As soon as you’re done with PEP, your healthcare provider can give you an HIV test and then get you started with PrEP immediately.

PEP prevents HIV after an exposure, but it does not prevent other sexually transmitted infections (STIs), since the medications used in PEP are antiretrovirals, drugs which are specifically acting against HIV.  

However, Doxy PEP (Doxycycline post-exposure prophylaxis) has recently become available. Doxy PEP is a short, preventative course of Doxycycline antibiotics you can take to prevent chlamydia, gonorrhea, and syphilis after an exposure. Doxy PEP involves taking 200 mg (one or two pills) of doxycycline, a common antibiotic. Doxy PEP must be taken within 24-72 hours of an exposure, and it is more effective the sooner you take it. For more information, visit this resource from the San Francisco AIDS Foundation or this resource from the San Francisco City Clinic.

It is safe and effective to take Doxy PEP alongside PEP, PrEP, and emergency contraception.