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PrEP: What Is HIV Prep & How it Works

Angela Sheddan

Medically reviewed by Angela Sheddan, DNP, FNP-BC

Written by Our Editorial Team

Last updated 8/20/2021

The AIDS epidemic of the 1980s and 1990s was a scary time for many underrepresented groups worldwide. 

The disease, which took years of research to fully understand, plagued communities of color, the gay community and those suffering from drug addiction. 

It was a source of fear — an unknown and silent killer. 

After more than 30 years, science has done incredible things to combat the HIV epidemic. We have medications that turn a once-fatal disease into a chronic condition (with proper treatment). 

We have a better understanding of sexually transmitted diseases and intravenously transmitted diseases. 

And for HIV-negative people who love HIV-positive people, we even have preventative medications to stop the disease from continuing its spread. 

Whether you’re with a partner who contracted HIV, or an intravenous drug user worried about transmission of HIV, there are ways to protect yourself and take measures to put your health first. 

Enter, daily PrEP medication.

What Is PrEP?

PrEP stands for Pre-Exposure Prophylaxis, which is a medicine for people at risk of HIV exposure to take preventatively before sexual contact to avoid contracting HIV. 

In other words, this is a medication for HIV-negative people who want to stay HIV-negative while engaging in certain activities (most often sexual activity with a positive partner, or intravenous drug use).

PrEP works as a preventative medication — you take it daily and build up a supply of it in your bloodstream, which in turn prevents the HIV virus from infecting your blood.

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Is PrEP Effective in Preventing HIV?

When taken properly, the CDC says daily PrEP is safe and highly effective in preventing the user from contracting HIV. 

PrEP reduces the risk of getting HIV from sexual activity by 99 percent, though there is less information available about whether it can help intravenous drug users. 

The CDC only shares data promoting a 74-percent effective rate for drug users who inject. 

When not taken as prescribed, the drug becomes much less effective, and the results are not guaranteed.

How to Take Daily PrEP for HIV Prevention

Depending on the potential source (and means) of HIV transmission, daily PrEP users should be aware of some different data about effective prevention. 

For instance, PrEP reached maximum protection ability for people who have anal sex after approximately one week, or seven days. 

For injection drug use and vaginal sex, however, the recommended period before PrEP reaches maximum effectiveness is three weeks, or about 21 days.

The CDC does not share data or recommendations for insertive or penetrating anal or vaginal sex.

There are two main medications with FDA approval under the PrEP banner: Truvada® and Descovy®. Both forms of PrEP are prescribed as a once-daily pill taken orally, but they have some key differences. 

Truvada, for instance, is effective and safe for everyone, while Descovy is not recommended for people who are assigned female at birth and are at risk of HIV transmission from vaginal sex.

Pills, however, are not the only effective means of treatment. A 2020 NIH study found that long-lasting injectable form of prevention outperformed daily oral medications, particularly for men and transgender women.

Things to Be Careful About with PrEP

Pre-Exposure Prophylaxis treatments are incredibly powerful medications that prevent contraction of a potentially deadly virus, so it makes sense that there are side effects and other cautions you’ll need to be aware of if you begin taking them. 

Let’s talk about side effects of PrEP first, which tend to be mild to moderate.

In addition to the risks of incorrectly taking PrEP (which include contracting HIV), side effects may include nausea, diarrhea, stomach pain, headache and fatigue. 

These side effects usually go away over time, but if they don’t or become worse, you should contact your healthcare provider.

Once you begin taking daily PrEP, there are further rules you’ll need to abide by. 

The CDC recommends regular visits to your healthcare provider for a follow-up appointment at three-month intervals, during which time they’ll assess the effectiveness and any issues related to your treatment. 

This is the time when you’ll be tested again for HIV, receive refills and discuss issues with the medication.

The CDC says telemedicine is an effective way to handle these meetings, and a specimen kit can be obtained and sent in, meaning an appointment is not necessary.

People tend to stop taking PrEP medications if risk of HIV exposure drops (in other words, if they break up with your HIV-positive sexual partner or discontinue drug usage), or if side effects are too severe. 

In the case of the latter, other prevention methods are recommended, and will likely include prophylaxis like condoms, at the very least. 

It’s recommended that multiple protective actions are taken by HIV-negative people who are interacting with HIV-positive partners, so using PrEP with condoms is a great way to double your protection against contracting HIV. 

It’s also worth noting that daily PrEP doesn’t prevent any other STIs, so using protection is still imperative.

PrEP is not a “morning-after” pill for HIV exposure — you don’t, for instance, take it once after a worrisome encounter or exposure. A single pill will have little or no effect on your chances of contracting HIV.

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PrEP, HIV and You

Whether your HIV risk is sexual or due to drug use, there’s no reason to feel embarrassed, judged or ashamed. There are bountiful, important reasons to consult a healthcare professional for this and other treatments. 

For intravenous drug users, your addiction is not a reason for anyone (including yourself) to think that you don’t deserve to be safe and healthy. 

A healthcare professional will be able to talk you through your protection options — shame-free — and answer any questions about PrEp, as well as help you lead a better, more confident life, and focus on the things that are important — like seeking help. 

The same goes for people in relationships with HIV-positive partners — HIV may have carried a stigma decades ago, but no good person judges someone for being exposed to HIV today. You already know that — you love your partner. 

They deserve your love, and you deserve theirs. You both also deserve protection and proper healthcare. Seek it out, take care of the ones you love. And yes, that includes yourself.

2 Sources

Hims & Hers has strict sourcing guidelines to ensure our content is accurate and current. We rely on peer-reviewed studies, academic research institutions, and medical associations. We strive to use primary sources and refrain from using tertiary references.

  1. Centers for Disease Control and Prevention. (2021, May 13). Prep. Centers for Disease Control and Prevention.
  2. U.S. Department of Health and Human Services. (2020, July 23). Long-acting injectable form of HIV PREVENTION outperforms daily pill in NIH study. National Institutes of Health.

This article is for informational purposes only and does not constitute medical advice. The information contained herein is not a substitute for and should never be relied upon for professional medical advice. Always talk to your doctor about the risks and benefits of any treatment. Learn more about our editorial standards here.