10 Questions and Answers About PrEP, the HIV Prevention Pill

When PrEP, the HIV prevention pill, was approved in the United States in 2012, it was met with controversy and confusion. But the truth is, there’s nothing controversial or confusing about this important HIV prevention tool.

PrEP is a tool that people who are not living with HIV can use to reduce their chance of becoming HIV positive. PrEP works even if you have sex with someone who is HIV positive and don’t use other forms of protection, like condoms.

PrEP works for all different types of people from all different walks of life. More than 150,000 people in the United States are already taking PrEP, and experts estimate that more than 1 million more are eligible.

PrEP is only available with a prescription. Doctors will often only prescribe PrEP if a person is considered to be at high risk for HIV infection, meaning you may benefit from having an extra tool in your sexual health toolkit.

The important thing to remember about PrEP is that it is most effective when taken as prescribed. And, despite rumors you may have heard to the contrary, there’s nothing slutty or shameful about taking PrEP if you and your doctor agree it’s right for you.

What Is PrEP, and How Does It Work?

Technically, PrEP stands for pre-exposure prophylaxis, which is a term used to describe the strategy of taking medicine to prevent an infection. PrEP is not a vaccine, meaning it’s not a one-time shot that makes you immune to HIV for the rest of your life. Instead, it’s a pill that is generally taken daily.

Right now, PrEP is only available as a tablet you take by mouth. In the future, other forms of PrEP are likely to be available, including a long-acting injectable version.

For now, though, two specific drugs are approved in the U.S. as PrEP:

• Truvada, which is approved for use by all adults.
• Descovy, which is approved only for cisgender men who have sex with men and transgender women who have sex with men.

Both Truvada and Descovy were originally developed as part of a treatment regimen for people who are already living with HIV. But scientists quickly realized that they also work well at stopping HIV infection among people who are HIV negative.

These pills work because the medications within them congregate inside your body’s T cells—the same type of cells that HIV tries to attack first. The drugs disrupt HIV’s ability to gain access to those cells and transform them into HIV-making machines.

What’s the Evidence to Support PrEP?

PrEP has been studied in at least 15 large experimental trials that demonstrated it is safe and effective when taken correctly. It has been studied in gay and bisexual men, transgender women, and cisgender, heterosexual couples.

These studies found that PrEP reduces the risk of getting HIV through sex by 99% and reduces the risk of getting HIV by sharing needles or injection drug equipment by 74%, according to the U.S. Centers for Disease Control and Prevention (CDC).

But these studies also revealed that when it comes to PrEP, most people need to take it every day for it to work. The people in the studies who missed days were more likely to become HIV positive. That’s why PrEP is often just one part of a larger HIV prevention plan that includes regular check-ins with your doctor and periodic HIV testing to make sure you’re still negative.

It’s also worth noting that although PrEP can offer effective protection against HIV, it doesn’t protect people from other sexually transmitted infections (STIs), such as syphilis and gonorrhea. For people who are exposed to HIV through injection drug use, PrEP also won’t help prevent blood-borne infections like hepatitis C.

How Do I Get PrEP?

PrEP must be prescribed to you by a health care provider—usually a doctor, physician assistant, or nurse practitioner. It’s not available over the counter.

You don’t need to go specifically to an HIV doctor to get PrEP. In fact, many people get PrEP prescriptions from their primary care providers.

Before prescribing PrEP, a health care provider will usually go through a few steps with you to make sure it’s the right time for you to start taking it. These steps include:

• Talking with you about your sexual history and potential drug use. (This helps them figure out what your risk level for HIV is.)
• Giving you an HIV test. (This confirms you’re not already HIV positive.)
• Giving you a hepatitis B test. (This is because Truvada can also treat hep B—and hep B infections can flare back up if you start Truvada and then stop it later.)

This video on whether you need to go to a specialist for PrEP features Demetre Daskalakis, M.D., and is part of the #AskTheHIVDoc series by Greater Than AIDS.

What’s the Difference Between Truvada and Descovy?

Right now, people who are interested in PrEP have two options to choose from: Truvada and Descovy.

Truvada and Descovy are very similar drugs:

• Both are tablets you take by mouth.
• Both of them contain two HIV-fighting medications within each tablet.
• In fact, one of the two medications, emtricitabine, is used in both drugs.

The big difference between Truvada and Descovy is in the second medication contained within the tablet. Truvada contains a medication called tenofovir disoproxil fumarate (TDF), which has been used as part of HIV treatment regimens since 2001 under the brand name Viread. Descovy contains a much newer version of that medication: tenofovir alafenamide (TAF). (Descovy was approved in the U.S. as an HIV treatment in 2016, and was approved for use as PrEP in 2019.)

Both drugs work very well against HIV, both of them are very safe to take, and they’re both equally good as part of a PrEP regimen. What sets TDF apart from TAF is how they break down inside your body: TAF is designed to break down much more slowly than TDF in your blood, which appears to make it a little more friendly to bones and kidneys. We’ll get into this more in the next section.

[Related story: Truvada vs. Descovy: Which Is Better for PrEP?]

Is PrEP Safe? What Are the Side Effects?

PrEP is safe. Some people have been taking it to protect themselves from HIV more than five years, and researchers haven’t reported any significant long-term health effects. Truvada has also been reliably used in HIV treatment since 2004, and most people who have taken it for years have experienced no serious problems.

That said, like with just about any drug in existence, PrEP can potentially cause side effects in some people. In one of the major research studies comparing Truvada to Descovy for PrEP, about one in four people who started taking either drug felt a side effect during their first few weeks of taking it.

These are the most common side effects—all of which are usually mild and typically go away within one to three months:

• headache
• diarrhea
• gas (which can cause stomach pain and farting)
• nausea
• joint pain

In addition, Truvada and Descovy each have their own specific potential side effects—although, again, most people don’t experience any side effects at all:

• Truvada can cause slight changes in bone density and kidney function, although these are not serious in most people. (They’re generally only a potential concern for people who already have bone or kidney problems; in a major study, only 2% of people on Truvada for PrEP needed to stop the drug due to side effects.)

• Descovy is less likely than Truvada to cause bone and kidney problems, but it may cause some people to gain a small amount of weight (typically 2 or 3 pounds) or see slightly increased cholesterol numbers compared to people taking Truvada.

Anyone who takes PrEP will need to visit their doctor for regular check-ins, to make sure they are still HIV negative and to make sure they are treated quickly for any issues that may crop up.

How Do I Know If PrEP Is Right for Me?

PrEP isn’t for everyone. But it might be right for you, if you or your health care provider think you could be exposed to HIV in the future.

If any of these things apply to you, it’s possible you could benefit from PrEP:

• You have been treated for another STI, like syphilis or gonorrhea.
• You have taken the emergency HIV protection pill PEP (post-exposure prophylaxis) several times over the past year.
• You have one sex partner, and you don’t know their HIV status.
• You have multiple sex partners, especially if you’re not sure of their HIV status.
• You have one main sex partner who is HIV positive, and you aren’t certain whether they have an undetectable viral load. (HIV-positive people with an undetectable viral load can’t transmit the virus during sex.)
• You don’t use condoms consistently, or you have trouble negotiating condom use with your sex partners.
• You or your sex partners use injection drugs.
• You or your sex partners engage in sex work (which can include non-professional sex work, such as exchanging sex for money, drugs, or housing).

Right now, the majority of people on PrEP in the U.S. are gay and bisexual white men. But doctors agree that a lot of people who need PrEP are not getting it—particularly people of color, including cisgender and transgender men and women.

Truvada PrEP is approved for use by all adults. Because Descovy PrEP was only deeply studied in gay and bisexual men and transgender women, for the time being it is not approved for cisgender women.

Even if people in your community don’t take PrEP, it’s important to know that people from all walks of life—including people of all races, all sexual orientations, and all gender identities—might be good candidates. Your eligibility should not be determined by your zip code, gender, or sexual orientation. Taking PrEP is more about supporting your sexual health, and gauging how likely it is that you might be exposed to HIV.

Does PrEP Mean I Don’t Need Condoms?

Barrier protection such as condoms remain the best way to protect yourself from STIs, including HIV. But it’s also true that not everyone is willing or able to use condoms. For some people, it might not be safe to negotiate condom use during sexual encounters. Other people might rather forego condoms, for any number of important reasons.

If you use PrEP correctly, which means following the dosing schedule prescribed by your doctor, it is highly effective at preventing HIV infection, even if you have condomless sex with someone who is HIV positive. However, unlike condoms, PrEP cannot protect you against other STIs, such as syphilis, gonorrhea, and chlamydia. And studies show that if you have another untreated STI, it boosts the chance that you could become HIV positive.

The bottom line is: PrEP is one of several very effective tools you can use to reduce your HIV risk. The more tools you use, the further it can reduce your risk.

Can I Stop and Start PrEP Whenever I Want?

The answer to this is complicated. Officially, PrEP is approved in the U.S. for daily use. But reliable research has shown that another approach is safe and effective for some people. This is called “on-demand” or “2-1-1” PrEP.

Many doctors and scientists believe that on-demand PrEP is more of an option for people who have anal sex than people who have vaginal sex. It works like this:

• You take two PrEP tablets between 2 and 24 hours before you plan to have sex.
• 24 hours later, you take one PrEP tablet.
• After another 24 hours, you take one more PrEP tablet.
• You restart the cycle (or continue it) whenever you plan to have sex again.

The reason 2-1-1 PrEP is only considered for some people is that PrEP generally takes several days to be fully “topped up” throughout your body, offering you maximum HIV protection. This is particularly true for people who have vaginal sex: Studies have suggested that while PrEP generally needs about a week to be fully effective in the blood and rectal lining, it can take up to three weeks to reach that level in vaginal tissue.

This is why the 2-1-1 dosing approach tends only to be offered to cisgender men who have sex with men (MSM). Our best research to date has found that, while daily PrEP is about 99% effective, 2-1-1 PrEP is around 86% effective in MSM.

The bottom line is: Daily PrEP is the most effective way to guarantee protection. But if you’re interested in on-demand dosing, talk to your care provider to see if it applies to you. It can be an especially helpful option if you have a pretty reliable sense of when you’re likely to have sex.

For Emergencies, There’s Also PEP

Keep in mind that there is another medicine HIV-negative people can use to stay negative in a pinch. It’s called PEP, and it’s reserved for emergencies after a possible exposure to HIV that you didn’t anticipate.

PEP, which is short for post-exposure prophylaxis, is for people who are HIV negative and are not already taking PrEP. You would use PEP if you were exposed to HIV through condomless sex or injection drug use, and you think the other person might have HIV or you don’t know their status.

PEP must be started within 72 hours of a possible exposure. You take PEP every day for 28 days—unlike PrEP, PEP is a full HIV treatment regimen, just like you’d take if you had actually been diagnosed with HIV.

This video on PEP and PrEP featuring David Malebranche, M.D., is part of the #AskTheHIVDoc series by Greater Than AIDS, a public outreach program run by the Kaiser Family Foundation.

Is PrEP Only for People Who Have a Lot of Sex?

When Truvada was first approved for PrEP, some people started calling the people who take it “Truvada whores.” This is stigmatizing, false, and makes people afraid to ask their doctors about PrEP—all of which make it harder for us to end the HIV epidemic and can make life worse for people who are living with HIV.

People may want to protect themselves from HIV infection for a wide range of reasons, all of which are completely OK:

• They like to have sex with multiple sex partners.
• They have one partner who is HIV positive.
• They are navigating an addiction to opioids and want to protect themselves from HIV transmission through injection drug use.
• They just want that extra bit of assurance that they’re being safe, especially if they’re in a community of people where a lot of people are HIV positive.

The bottom line is: __Taking PrEP doesn’t mean anything about your promiscuity or your worth as a person. It just means you’re taking an important step to reduce your risk of HIV. __

Once I Start Taking PrEP, Do I Have to Keep Taking It for Life?

No. People change, their circumstances change, and so too does their need for PrEP.

You can stop taking PrEP if your situation changes and you think it’s unlikely you’ll be exposed to HIV for the foreseeable future. But similarly to starting PrEP, stopping is a decision you should make after talking it over with your health care provider.

Ultimately, PrEP is about having an extra tool to prevent HIV infection. Every person deserves to feel empowered to have sex in exactly the way they prefer. Educating yourself on the potential benefits of PrEP can help you make better choices about your sexual health.

The bottom line is: PrEP is a good HIV prevention tool that’s there for you when—and if—you need it.

Myles Helfand contributed reporting to this article.