One pill. Once a day.

PrEP now. Prevent HIV.

One PrEP pill a day is 92% effective at preventing HIV.


PrEP is a daily pill for HIV prevention.

PrEP (short for Pre-Exposure Prophylaxis) is a new way to prevent HIV. It’s a prescription medicine that, when taken every day, greatly reduces your risk of getting HIV by blocking the virus.

If you are HIV-negative and think you might be at risk of getting HIV, taking PrEP can give you protection and peace of mind.

PrEP does not protect against sexually transmitted diseases like gonorrhea or syphilis, so you should continue using condoms to prevent the spread of sexually transmitted diseases.

pill bottle


If you are HIV-negative and think you might be at risk of getting HIV, taking PrEP once a day can help you take control of your health.


You might be at risk of getting HIV if:

  • You have more than one sex partner.
  • You do not regularly use condoms.
  • You’re in an ongoing relationship with someone who has HIV.
  • You’re not sure if your sex partner is HIV-positive.
  • You or your sex partner have been diagnosed with a sexually transmitted infection in the past six months.
  • You have injected drugs in the past six months and have shared needles.

If you have a sex partner who is HIV-positive and are considering getting pregnant, talk to your doctor about PrEP. It may be an option to protect you and your baby.


PrEP works to prevent HIV by interfering with HIVs ability to copy itself in your body after exposure. This prevents the virus from establishing an infection and making you sick.

When taken every day, PrEP has shown to reduce the risk of HIV infection in people who are at high risk by more than 90%. PrEP is much less effective if not taken every day. PrEP can be more effective if combined with other ways to prevent HIV infection, like using condoms and drug abuse treatment.

how does prep work


If you think you may be at risk for HIV, talk to your healthcare provider about whether PrEP is right for you.

If your healthcare provider is unfamiliar with PrEP, AIDS Foundation Houston can connect you to PrEP services while your primary care doctor maintains your primary health needs.

If you have questions about PrEP, speak with an AFH PrEP Specialist between 9 am and 5 pm at 832-874-5380 or leave a message after hours and we’ll return your call.

Once PrEP is prescribed to you, you’ll need to return for blood work every three months. Your doctor will keep close track of any side effects, which are typically minor and not experienced by the majority of PrEP users.

PrEP is covered by Medicaid and most insurance programs.

If you do not have insurance, AIDS Foundation Houston can help you find programs that cover the cost of your appointments and blood tests, as well as co-pay assistance programs for the cost of your prescription.

PrEP should be taken daily. Remember, PrEP does not protect agains STDs like gonorrhea or syphilis. You should continue using condoms to prevent the spread of sexually transmitted diseases.

prescription pad


How long does PrEP take to work?

PrEP typically takes one to two weeks to provide full protection. It’s important to use a condom in the first two weeks of taking PrEP to make sure you’re protected against HIV.

Are there any side effects associated with daily PrEP use?

Most PrEP users don’t experience side effects. In your first few weeks of taking PrEP, you might experience minor symptoms such as fatigue, headache, abdominal pain and weight loss. These side effects should go away on their own.

A small number of PrEP users might be at increased risk for kidney disease. While you’re taking PrEP, your doctor will monitor your kidney function with routine blood tests every three months.

For a comprehensive overview of all possible side effects, including those that are uncommon and rare, click here.

If I take PrEP, can I stop using condoms?

Because PrEP only protects against HIV, we strongly suggest that you use condoms to prevent the spread of sexually transmitted diseases. Condoms can help you prevent things that PrEP can’t—like pregnancy, or STIs like gonorrhea and syphilis.

I think I’ve been exposed to HIV. Can I start taking PrEP to prevent infection?

No. PrEP (Pre-Exposure Prophylaxis) can only prevent HIV when taken consistently BEFORE exposure. PrEP cannot be started as a method of treatment AFTER an event of HIV exposure (such as sex without a condom, needle-sharing drug use, or sexual assault).

PEP (Post-Exposure Prophylaxis) is the 28-day treatment regimen recommended for people who’ve been exposed to HIV. If you think you have been exposed to HIV, it is important that you start taking PEP as soon as possible. PEP is only effective is taking within 36 hours (a day and a half) of HIV exposure.

If you are exposed to HIV during a weekend, or you cannot make an appointment for the next day with your primary care doctor, go to an emergency room for immediate treatment. Do not wait more than 36 hours to start PEP treatment.

If you are currently taking PEP, talk to your doctor before starting PrEP. Blood testing and a short wait time are required to make sure you are HIV-negative after finishing a PEP regimen.

What happens if I miss a dose or only take PrEP once in a while?

To be effective at preventing HIV, PrEP must be taken every day as prescribed by your doctor.

If you miss one dose, that’s okay. Take your next dose as planned.

If you miss two or three doses while you’re sexually active, or if you don’t take PrEP as prescribed, check in with your doctor to make sure that you’re still HIV-negative. You can restart your PrEP routine after you get a new negative HIV test.

What if my doctor doesn’t know about PrEP?

If your primary care doctor is unfamiliar with PrEP, call AIDS Foundation Houston at 713-623-6796. AIDS Foundation Houston can help you find PrEP services, so you may continue seeing your primary doctor for the rest of your health needs.

If you want your primary care doctor to handle your PrEP services, AIDS Foundation Houston can contact your doctor on your behalf to talk about what PrEP is, and how it might be beneficial to you.

Is PrEP a vaccine?

No, PrEP is not a vaccine. A vaccine provides immunity against an illness for a long period of time with no daily upkeep.

PrEP is a daily pill that, when taken as prescribed, greatly reduces your risk of getting HIV. PrEP does not provide immunity against HIV; as soon as you stop taking PrEP, you lose protection against the HIV virus. PrEP has to be taken every day for optimal protection against HIV.

I am a heterosexual woman who is HIV-negative. I want to have a baby with my partner who is HIV-positive. Can PrEP protect my baby and me against HIV?

Yes. PrEP is one of several recommended options available to prevent the transmission of HIV. Talk to your primary care doctor for more information on the options available to you.

I want to take PrEP and I have insurance. Is PrEP covered by my plan?

PrEP is covered by Medicaid and most insurance programs. Co-pay assistance programs are available. Call AIDS Foundation Houston at 713-623-6796 for more information about co-pay assistance.

Does PrEP interfere with my birth control pill?

To date, research shows that hormone-based birth control drugs do NOT interact with PrEP. As advocated by the U.S. Women and PrEP Working Group, a coalition of more than 50 women from leading AIDS and women’s health organizations, more research needs to be done studying women and their prevention choices to avoid both HIV infection and pregnancy.

How effective at preventing HIV is PrEP?

If taken correctly and consistently, PrEP is 92%–99% effective in reducing your risk for HIV.

How long does it take PrEP to become effective after you start taking it? How long does it take to become protective?

It’s estimated that it takes at least seven days for PrEP to reach high levels of protection in the body. When used correctly, PrEP provides 92%–99% reduction in HIV risk for HIV-negative individuals who take the pills every day as directed.

Once you start using PrEP, do you have to use PrEP forever?

No. We recognize that people go in and out of “seasons of risk,” where there are certain times it makes sense to take PrEP and then other times where it doesn’t make sense to take PrEP.

For example, if you start taking PrEP because you are sexually active with multiple partners who are HIV-positive and HIV-negative, and later you find yourself in a relationship where you and an HIV-negative partner are committed to having sex with only each other, then continuing to take PrEP might not make a whole lot of sense for you.

Or maybe you start PrEP when you are in a relationship, then that relationship ends and you have no sexual partner for the next six months; then it might not make sense to take PrEP.

Or more simply, maybe you decide to use other options to reduce your risk for getting infected with HIV, and PrEP doesn’t make the most sense at the moment.

With proper guidance, people can safely start and stop taking PrEP. Think of PrEP as an HIV prevention option where HIV-negative individuals take a pill to prevent HIV infection for the “season” when they are most at risk for being exposed to HIV.

If I’m not having sex right now, do I still need to take PrEP?

If you feel your risk for HIV has changed recently and it doesn’t make sense for you to take PrEP anymore, then talk to your doctor about discontinuing PrEP. If you’re just experiencing a temporary “lull” in your sex life lasting less than a month or two and expect to be sexually active again in the near future, it may not be advisable to discontinue PrEP. Ask your doctor.