PrEP: A Quick and Dirty Guide to the Pill that Prevents HIV

Kyan Lynch, MD, MA


Frequently Asked Questions about PrEP



Question 1: What is PrEP?

PrEP is an idea. It's the notion that a person can take a medication before being exposed to a disease and prevent an infection from occurring. If you want another example of PrEP, think malaria. We've been offering pre-exposure prophylaxis for malaria since the mid 1800s!


PrEP for HIV, specifically, has been available since 2012. That's the year that the FDA approved Truvada, a once-a-day pill, for HIV prevention.


While Truvada is the only option for PrEP today, that won't always be the case. As I type, different pills, injections, inserts, and vaginal rings are being tested and will likely be available in the not-too-distant future!



Question 2: Who Can Use PrEP?

The short answer is: anyone who is HIV negative and at risk for acquiring HIV.


The long(er) answer is:

  • HIV negative folks who have sex (a) with multiple partners (b) don't always use barrier protection such as condoms, and (c) don't always know that their partners are HIV negative

  • HIV negative persons who are in a sexual relationship with an HIV+ partner

  • Men who have sex with men, and cisgender women who have sex with men who have sex with men (say that 10x fast)

  • Transgender folks who are at risk due to sexual behavior or drug use

  • People who use IV drugs, and partners of people who use injection drugs

  • Sex workers, and partners of sex workers

  • People who use drugs such as cocaine, methamphetamines, GHB, ecstasy, PCP, poppers, marijuana, and alcohol to alter their consciousness or augment partying

  • Anyone diagnosed with a sexually transmitted infection in the last year

  • Any HIV negative person who wants PrEP

  • And... as of May 15th, 2018... adolescents at risk for HIV!

Does that sound like pretty much everyone you know? Yep. Spread the word!




Question 3: Is PrEP Safe?

In general, PrEP is a safe medication. Some people who go on PrEP can score lower on bone density tests, even though they may not notice the change, and in some cases, PrEP can cause kidneys to work less efficiently. Fortunately, studies show that these effects go away once you stop taking PrEP.


To make sure you stay healthy while taking PrEP, it's important to get your labs drawn before you start PrEP, and every 3 months while you stay on PrEP.

PrEP is NEVER to be prescribed for HIV+ people. That's because Truvada alone is not enough to fight the infection. Before you start PrEP, you will be tested for HIV. If you are HIV negative and start PrEP, your provider will re-check your HIV status every 3 months.


Question 4: Does PrEP Have Side Effects?

Yes, PrEP can cause side effects, although the side effects are usually self-limited, lasting anywhere from a few days up to 3 months. The most common side effects are: stomach aches, gas, loose stools, headaches, and weight loss. If you experience some side effects from PrEP, you can ask your provider if there are ways to help you feel better until those side effects go away on their own. For example, some PrEP users find that they feel better when they take Truvada on a full stomach, rather than an empty one.


Question 5: How Often Do I Have to Take PrEP?

PrEP is a once-a-day, EVERYDAY medication. If you want it to work, you gotta take it. It's that simple.


Question 6: How Long Does PrEP Take to Work?

Interestingly, it depends upon the way in which you are being exposed to HIV. If you are at risk because of anal sex, you need to be on PrEP for 7 days before it starts working. If you are at risk because of vaginal sex, it takes 21 days to start working.


Questions remain for trans women who have had bottom surgery. While research is conducted, it is better to assume that the medication will take 21 days to work.


Question 7: How Does PrEP Work?

Truvada is two medications combined inside of one pill. Both medications are called anti-retrovirals, and they work to stop HIV from being able to hijack healthy cells and reproduce. When viruses can't reproduce, they can't cause an infection, and our bodies wash them out.

The BEST way to prevent HIV is to also use a condom or other barrier method, so that HIV can't even get in the body.


Question 8: How Well Does PrEP Work?

PrEP, in the form of Truvada, is very effective at preventing HIV. When taken every day, studies show PrEP can reduce a person’s risk of getting HIV by up to 99%.


Question 9: What if I've Already Been Exposed to HIV? Or I'm Exposed Before PrEP Starts to Work?

That's where post-exposure prophylaxis, or PEP, comes in. PEP is a combination of medications that people take for 28 days after they have been exposed to HIV.

If possible, it's always better to be on PrEP instead of waiting to use PEP from time-to-time when exposed. PEP has nastier side effects (nausea, vomiting), requires more medications, and needs to be taken IMMEDIATELY after you are exposed to HIV.




Question 10: Do I Have to Stay on PrEP Forever?

PrEP does not need to be a life-long medication. Rather, PrEP is there for you when you want it, and you can stop taking it whenever you and your provider decide it’s no longer necessary. Typically, PrEP is prescribed at 3-month intervals, and you can check in with your medical provider about staying on PrEP every visit if you would like.


Some reasons why people decide to stop taking PrEP include: entering into a monogamous relationship with a person who is HIV negative, or a person who has HIV but is unable to transmit the virus, exiting a relationship with a person known to have transmittable HIV, pregnancy (some people choose to stay on PrEP during pregnancy), no longer having sex, and no longer using injection or other drugs.


Your need for HIV prevention strategies is unique to you, and will likely change over the course of your life. That is why the decision to start or stop PrEP should be made by you, with input from your provider.


Question 11: Where's the Proof?

Truvada was approved as a medication to prevent HIV by the Food and Drug Administration (FDA) in 2012. The FDA scientists decided to approve Truvada for HIV prevention based upon several large studies which proved that Truvada is both safe and effective when taken appropriately. Since then, dozens of additional studies have been published confirming these results, and discovering new ways to teach people about PrEP, and to help people remember to take the pill daily.


PrEP is no longer considered experimental. PrEP has proven itself as a scientific breakthrough and has been used successfully by thousands of individuals around the world.


Question 12: Does PrEP Interfere with Hormones for Gender Transition?

Right now, the best answer I can give is probably not. So far, there is no reason to believe that taking PrEP would impact hormone therapy in any way. In fact, there are some reasons to believe that PrEP and hormone therapy would get along nicely. For example, studies show that PrEP can be safely taken with hormone-based birth control.


Fortunately, some really smart people are currently answering this question directly in placebo-controlled studies. When I know more, you will too.


For more info, check out this pdf from Callen-Lorde.


Bonus Question: What is HIV?

HIV stands for Human Immunodeficiency Virus. This name tells us a lot of information. The first word, human, is pretty clear: this is something that can cause problems for humans. The last word, virus, is also straightforward. HIV is a virus. Viruses are infectious agents (sometimes referred to as “bugs”) which find their way into the body and hijack healthy cells, forcing them to start producing more virus. Different viruses cause different symptoms. For example, the cold virus can cause a runny nose and sore throat, while gastrointestinal viruses can cause vomiting, upset stomach, and diarrhea. In the case of these and many other viruses, a healthy body can fight off the infection, and you only have to experience these nasty effects for a few days.


In the case of HIV, the middle word, immunodeficiency, tells a more detailed story. The first part, immuno-, refers to the immune system. The immune system is a collaborative network of cells and organs in your body that fights off infections and keeps you healthy. You can think of the immune system as your own personal army. Deficiency means weakened, defective, ineffective. So, HIV is a virus that attacks humans by weakening the immune system – and we got all that from a name!


So now we know what HIV does, but how does it do it? As mentioned earlier, the first phase of any virus’ mission is getting into the body. This isn’t as easy as it sounds. HIV can’t get through your skin into your body, nor can it survive outside of the body for long. But HIV is clever. HIV can’t get into your body all by itself, so HIV must hitch a ride. HIV hides in an infected person’s bodily fluids, such as blood, semen, rectal secretions, vaginal secretions, and breast milk. When these bodily fluids get past another person’s skin barrier, through sex, injection with a needle, breastfeeding, or through a cut or break in the skin, the HIV spreads and infects the new person.


Once inside the body, HIV goes right to work attacking the immune system. HIV does this directly, by going after a specific type of immune system fighter: the T cell. If HIV is not treated properly and early, it can cause so much damage to the immune system that a body can’t even fight off the average cold and gastrointestinal infections mentioned earlier. When HIV goes unchecked, these simple viruses become deadly. When HIV has progressed this far, it has officially caused a disease known as the Acquired Immune Deficiency Syndrome, otherwise known as AIDS.




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