PrEP is daily or on-demand medicine that HIV-negative people take to prevent infection before exposure. You have two main forms: oral pills (Truvada or Descovy) and an injectable, cabotegravir (Apretude). Pills can be taken daily or, for some, on-demand; the shot replaces pills with periodic injections for people who'd rather not take a daily tablet.
risk reduction, taken as prescribed
daily Truvada/Descovy or the Apretude injection
not other STIs or pregnancy
| Item | Value |
|---|---|
| From sex | ~99% — risk reduction, taken as prescribed |
| From injection use | ≥74% |
| Forms | pill or shot — daily Truvada/Descovy or the Apretude injection |
| Protects against | HIV only — not other STIs or pregnancy |
What each option actually is
PrEP stands for pre-exposure prophylaxis — medicine you take before a possible exposure to keep HIV from taking hold in your body CDC, Talk PrEP Together. It's prevention, not treatment, and it's for people who are HIV-negative. Don't confuse it with PEP, the emergency course you start after a single possible exposure; the two aren't interchangeable, and PEP is a stopgap, not an ongoing plan CDC, Preventing HIV with PEP.
One thing PrEP does not do: it protects only against HIV. It won't stop chlamydia, gonorrhea, or syphilis, and it doesn't prevent pregnancy. That's why people on PrEP keep using condoms when they want STI protection and keep up routine screening — more on that below.
Daily oral pills (Truvada and Descovy)
Oral PrEP is a once-a-day tablet. Truvada is approved for people at risk through sex or injection drug use. Descovy is approved for those at risk through sex only — it's not recommended for people assigned female at birth who are at risk through receptive vaginal sex. Both are taken on an ongoing schedule; the difference between the two molecules is worth understanding if you're weighing kidney and bone effects, which we cover in truvada vs descovy.
On-demand (2-1-1) dosing
Some people who don't want a daily habit use "on-demand" oral PrEP — sometimes called 2-1-1 — where pills are timed around a planned sexual exposure rather than taken every single day. This approach has been studied mainly for receptive anal sex, and it requires planning ahead because the medicine needs lead time to reach protective levels. It's not a morning-after option, and it isn't appropriate for injection-drug risk. Ask a clinician whether your situation fits this schedule before you rely on it.
Injectable cabotegravir (Apretude)
Apretude is the injectable form — cabotegravir given as a shot rather than a daily pill. It's for people at risk through sex who weigh at least 77 pounds (about 35 kg). The appeal is simple: no daily tablet to remember and no pill bottle to carry. Like the pills, it protects against HIV only, so STI screening and other prevention still matter. The shot is given by a clinician, which means your protection is tied to keeping your injection appointments on schedule.
The key differences
How well PrEP works depends on taking it correctly. Oral PrEP reduces the risk of getting HIV from sex by about 99% when taken as prescribed. For injection drug use, the pills cut risk by at least 74% when taken as prescribed. The headline takeaway: adherence is everything — a pill skipped is protection lost.
Protection also isn't instant, and the lead time depends on the kind of exposure. It takes about 7 days of consistent dosing to reach maximum protection for receptive anal sex, and about 21 days for receptive vaginal sex and for injection drug use. That ramp-up is exactly why PrEP can't double as emergency protection after a one-off exposure — if you've already had a possible exposure, see when to test after exposure and ask about PEP instead.
The biggest practical split between pills and the shot is the rhythm of your life. Pills put the schedule in your hands every day; the injectable hands it to your clinic calendar. Both work when followed; neither works when forgotten.
Pills vs injectable PrEP, side by side
| Feature | Oral pills (Truvada / Descovy) | Injectable (Apretude / cabotegravir) |
|---|---|---|
| Form | Daily tablet (or on-demand for some) | Clinician-administered shot |
| Who it's for | Truvada: sex or injection risk. Descovy: sex only (not for receptive vaginal risk in people assigned female at birth) | People at risk through sex who weigh at least 77 lb (35 kg) |
| Effectiveness against HIV from sex | About 99% when taken as prescribed | For sexual risk |
| Effectiveness for injection drug use | At least 74% (pills) when taken as prescribed | Not indicated for injection-drug risk |
| Daily pill needed? | Yes (or on-demand timing) | No |
| Best for | People comfortable with a daily routine or planned 2-1-1 dosing | People who prefer not to take a daily pill |
| Protects against other STIs / pregnancy? | No | No |
Which one fits you — how to choose
Start with your risk route. If any of your risk comes from injection drug use, the pills (specifically Truvada) are your route — the shot and Descovy aren't options there. If your risk is sexual and you'd genuinely struggle to take a pill every day, the injectable removes that daily decision and may be the more reliable choice for you, because the best PrEP is the one you'll actually stick with.
- Choose a daily pill if you want flexibility, are comfortable with a routine, or have injection-drug risk (Truvada).
- Consider on-demand (2-1-1) pills if your exposures are infrequent and predictable, and a clinician confirms you're a candidate.
- Consider the injectable if remembering a daily pill is your weak spot and your risk is sexual — and you can keep regular appointments.
- Whichever you pick, plan to keep using condoms for STI protection and to keep testing on schedule.
It's also worth knowing that prevention isn't only about your own medicine — when people living with HIV start treatment early and reach an undetectable viral load, they don't transmit the virus through sex. That's the principle behind why earlier hiv treatment can help prevention across a whole community.
The practical next step
Starting PrEP begins with an HIV test, because PrEP is for HIV-negative people — taking it while already infected can cause resistance. After that, expect regular check-ins while you're on it: repeat HIV testing, kidney monitoring with the pills, and STI screening, since PrEP doesn't cover other infections. You can get PrEP through a primary care office, a sexual-health clinic, or telehealth, and patient-assistance programs exist to bring the cost down, often to little or nothing for people who qualify.
A note on a mistake I see often: people treat PrEP like a morning-after pill. It only works on an ongoing schedule, and it ramps up over days — so it can't rescue you after last night. If you need protection on the same day you don't yet have it, when to test after exposure and the PEP route are what to ask about. And because PrEP leaves you exposed to everything except HIV, make routine screening part of the plan — you can get tested alongside your PrEP visits.
When to talk to a clinician
Reach out if you're HIV-negative and have ongoing risk through sex or injection drug use, if you've had a recent possible exposure (so they can sort out PrEP versus PEP), or if you're on PrEP and notice side effects, missed doses, or new symptoms. A short conversation settles which form fits your body, your routine, and your insurance — and gets the first HIV test on the books.