PrEP is a daily pill (or injection) that reduces the risk of getting HIV from sex by about 99% when taken as prescribed. There are several ways to take it, and the right method depends on your body, your risk factors, and your preferences. Here’s what you need to know to use PrEP correctly.
Types of PrEP Available
Four medications are FDA-approved for PrEP. The two most common are oral pills: Truvada (tenofovir DF-emtricitabine) and Descovy (tenofovir alafenamide-emtricitabine). Both are single tablets containing two active drugs. You take one pill per day.
If you’d rather skip daily pills, there’s an injectable option called Apretude (cabotegravir). It’s given as a shot by a healthcare provider. A newer injectable option, lenacapavir, is also FDA-approved and requires even fewer visits.
How to Take Daily Oral PrEP
Take one pill at roughly the same time each day. You can take it with or without food, though some people find it easier on the stomach with a meal. There’s no strict rule about morning versus evening; pick whichever time fits your routine and helps you remember.
Consistency matters more than perfection. If you miss a dose, take it as soon as you remember. The one exception: if it’s almost time for your next dose, skip the missed one and resume your normal schedule. Don’t double up by taking two pills within a few hours of each other.
PrEP doesn’t work instantly. It takes several days of consistent use to build up protective drug levels in different body tissues. For receptive anal sex, protection reaches high levels after about 7 days of daily use. For receptive vaginal sex and for people who inject drugs, it takes longer, closer to 21 days. During that initial window, use other protection like condoms.
The 2-1-1 “On-Demand” Option
If you don’t have sex frequently enough to justify a daily pill, on-demand PrEP (also called the 2-1-1 method) is an alternative. This approach has been studied specifically for men who have sex with men and involves Truvada only, not Descovy.
The schedule works like this:
- Before sex: Take 2 pills between 2 and 24 hours before anticipated sex.
- First follow-up: Take 1 pill 24 hours after that first double dose.
- Second follow-up: Take 1 pill 24 hours after the second dose.
That’s a minimum of 4 pills covering a single sexual encounter. If you continue having sex over several days, you keep taking one pill daily until 48 hours after your last sexual contact, then take the final dose 24 hours later.
How Injectable PrEP Works
Apretude is given as an intramuscular injection in the buttock. The schedule starts with two initiation shots given one month apart, then switches to one shot every two months. Your provider may have you take a daily oral tablet of the same drug for about a month before the first injection, just to make sure you tolerate it well.
The main advantage is obvious: no daily pill to remember. The tradeoff is that you need to keep your injection appointments on schedule. Among people who inject drugs, oral PrEP reduces HIV risk by at least 74% when taken as prescribed; injectable PrEP removes the adherence challenge that can lower that number.
What Happens Before You Start
You can’t just pick up PrEP at a pharmacy. A few tests are required first. The most important is an HIV test, because PrEP is only for people who are HIV-negative. Taking PrEP while unknowingly HIV-positive can lead to drug resistance, making HIV harder to treat later. Providers use a blood-based test rather than an oral rapid test, since blood tests are more sensitive at catching recent infections.
Beyond HIV, your provider will typically screen for chlamydia, gonorrhea, and syphilis. If you’re taking either oral PrEP pill, a kidney function test is required because both formulations can affect the kidneys. Truvada requires a higher baseline kidney function than Descovy, which is one reason providers sometimes choose one over the other. Hepatitis B screening is also standard, and if you’re prescribed Descovy specifically, a cholesterol and triglyceride check may be added.
These aren’t one-time tests. You’ll repeat HIV testing and other labs at follow-up visits, typically every three months.
Side Effects and the “Start-Up Syndrome”
About 16% of people experience what’s known as start-up syndrome when beginning oral PrEP. Symptoms peak within the first month and typically resolve by month three. The most common complaints in clinical trials were nausea (5 to 19% of users), dizziness (15%), fatigue (11%), abdominal pain (5 to 13%), gas, and occasional vomiting.
These side effects are real but temporary for most people. If nausea is an issue, taking the pill with food can help. The discomfort is mild enough that it only modestly affects whether people stick with the medication. If symptoms persist beyond three months or feel severe, that’s worth raising with your provider, as switching formulations may help.
How to Stop PrEP Safely
You can’t just quit PrEP the day you decide to stop. Drug levels need to remain protective long enough to cover your most recent exposure. Guidelines vary slightly by organization, but the general principle is the same: keep taking your pills for a buffer period after your last potential HIV exposure.
The CDC recommends continuing for 7 to 10 days after your last exposure. The World Health Organization is more conservative, recommending 28 days. For people whose risk comes through receptive anal sex, some guidelines allow stopping as soon as 48 hours after the last sexual contact, while vaginal sex exposure calls for at least 7 days of continued use. The safest approach is to discuss a specific stop date with your provider.
One important note: both Truvada and Descovy contain drugs that are also active against hepatitis B. If you have hepatitis B (even without knowing it), stopping PrEP abruptly can cause a flare of liver inflammation. This is another reason the initial hepatitis B screening matters, and why stopping should be a planned decision rather than something you do on your own.