If you stop taking PrEP, the medicine clears from your body over days and your protection against HIV fades. Once levels drop, you're no longer shielded. PrEP works only while it's in your system on an ongoing schedule, so any sex or injection-drug exposure after you stop carries your usual HIV risk again. Restarting takes time to rebuild full protection.
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 |
The short version: protection fades, it doesn't vanish instantly
PrEP (pre-exposure prophylaxis) is medicine HIV-negative people take before a possible exposure to keep HIV from taking hold CDC PrEP. It prevents infection rather than curing it, and it only protects you while the drug is circulating at protective levels. When you stop, those levels decline and your defenses come down with them. There's no single moment where you go from fully protected to fully exposed. Protection tapers off, and how long that tail lasts depends on the medicine and the type of exposure. Don't time your last dose to a planned encounter, and if you've stopped and want protection again, plan to restart well ahead of any risk.
What PrEP is and how it works
PrEP keeps a steady level of antiretroviral medicine in the cells and tissues HIV would try to infect. If the virus shows up, the drug blocks it from copying itself and establishing an infection. It has to be on board before exposure, because the medicine needs to already be sitting in the right tissues. PrEP is different from PEP (post-exposure prophylaxis), the emergency course you start after a single possible exposure; the two aren't interchangeable CDC PEP. PrEP is the ongoing plan; PEP is the fire extinguisher.
How well PrEP works — and what stopping changes
Taken as prescribed, PrEP reduces the risk of getting HIV from sex by about 99%, and it cuts the risk from injection drug use by at least 74%. Those numbers describe consistent use, and they don't carry over after the last dose. The tissues also don't reach full protection the moment you start, which tells you what happens when you stop in reverse:
- For receptive anal sex, daily oral PrEP reaches maximum protection in about 7 days, so rectal tissue both protects and clears relatively quickly.
- For receptive vaginal sex and for injection drug use, it takes about 21 days to reach maximum protection. These tissues build up slowly, and by the same logic, you shouldn't assume protection ends the instant you skip a dose.
- Because the drop-off mirrors the ramp-up, stopping leaves a brief residual window before levels fall below protective. Don't rely on it as cover for an exposure.
If your risk hasn't changed but your PrEP seems less reliable — missed doses, side effects, or doubts about whether it's working — that's a conversation worth having, since prep may not be working as it should for some users in specific situations.
How to use it, who it's for, and how to stop or restart safely
PrEP is for HIV-negative people who could be exposed through sex or injection drug use. There are pills and a shot:
- Truvada — a daily oral pill for people at risk through sex or injection drug use.
- Descovy — a daily oral pill for those at risk through sex only; it's not for people assigned female at birth who are at risk through receptive vaginal sex.
- Apretude (cabotegravir) — an injectable for people at risk through sex who weigh at least 77 pounds (35 kg), a good fit if you'd rather not take a daily pill.
In practice, starting PrEP begins with an HIV test, because PrEP alone isn't enough to treat an existing infection and using it that way can cause problems. After that, you stay on a schedule and check in with your clinician regularly. Stopping isn't a medical emergency, but do it deliberately. Tell your prescriber, keep covering exposures (with condoms, for instance) during the tail period, and don't quit mid-week thinking you're still protected for the weekend. If you restart later, you'll need to rebuild protective levels. Count on roughly the same ramp-up times above before you're back to full coverage, and your clinician will repeat an HIV test first.
A common mistake is treating PrEP like a morning-after pill. It only works taken on an ongoing schedule. One tablet the day before a hookup doesn't do it, and stopping for a stretch means you're not covered until you've restarted and rebuilt levels.
Cost and how to get it
You can get PrEP from a primary-care clinic, sexual-health clinic, or many telehealth services, and assistance programs exist to cover the cost for people who are uninsured or underinsured. If money or access is the reason you're thinking about stopping, ask about those programs before you quit. Staying on consistently protects far better than an on-and-off pattern.
What PrEP does NOT protect against
PrEP guards against HIV and nothing else. It does not protect against other STIs — chlamydia, gonorrhea, or syphilis — and it does not prevent pregnancy. This matters whether you're on PrEP or have just stopped: people on PrEP still need routine STI screening, and the same is true the moment you come off it. If you've stopped and had an exposure, an HIV-only mindset leaves blind spots, so plan to get tested for the full panel rather than assuming PrEP had you covered.
How PrEP fits with the rest of your prevention
PrEP works best as one layer, not the whole wall. Condoms add protection against the STIs and pregnancy PrEP ignores, regular testing catches anything early, and vaccines such as hepatitis B and HPV close other gaps. Treatment is part of prevention too. When partners living with HIV are on effective therapy with an undetectable viral load, they don't transmit the virus sexually, and earlier hiv treatment can help prevention across a whole community. If you stop PrEP, lean harder on these other layers to fill the gap.
When to talk to a clinician
Reach out before you stop if you can, and definitely if you've already stopped and then had a possible HIV exposure. That may be a situation for PEP, which has to start quickly after exposure to work. Also check in if your risk is changing, if side effects are pushing you to quit, or if you want to switch from a daily pill to the shot. Timing matters for testing, so review when to test after exposure so you don't test too early and get false reassurance.