The 2-1-1 rule is an on-demand way to take PrEP for HIV prevention without
taking a pill every day. Here’s how it works: take 2 pills 2-24 hours before sex, then 1 pill
24 hours later, then 1 more pill 24 hours after that. This method is also called event-based
PrEP or on-demand PrEP.
It’s recommended for cisgender men who have sex with men and is backed by the
IPERGAY study, which found it to be about 86% effective at preventing HIV. It’s not
recommended for people with vaginal exposure to HIV, as the medication needs more
time to reach protective levels in vaginal tissue.
Below, we’ll walk through the exact dosing schedule, who it’s for, how it compares to daily
PrEP, and how to get started.
The 2-1-1 PrEP Schedule at a Glance
Interested in on-demand PrEP? Talk to MISTR to find out if the 2-1-1
method is right for you.
The 2-1-1 method (also called event-based PrEP or on-demand PrEP) lets you take PrEP only when you need it, instead of every day. Here’s the schedule:
Example: If you take your first two pills on Friday at 6 PM, take one pill on Saturday at 6 PM, and one more on Sunday at 6 PM. The timing doesn’t have to be exact to the minute, but stay as close to the 24-hour window as you can.
Important: This method only works with Truvada (tenofovir disoproxil fumarate/emtricitabine). It does NOT work with Descovy. If you’re currently on Descovy and interested in on-demand PrEP, talk to your provider about switching. What if you have sex again during the cycle? Keep taking one pill every 24 hours until 48 hours have passed since your last sexual encounter. You’re extending the protection
by continuing the daily doses.
The 2-1-1 method has been studied and shown to work for a specific group. Here’s who
it’s for and who should stick with daily PrEP:
2-1-1 is recommended for:
2-1-1 is NOT recommended for:
The evidence comes from the IPERGAY study, conducted in France and Canada, which found event-based PrEP to be about 86% effective at preventing HIV in cisgender men who have sex with men.
If you’re not sure which method is right for you, talk to a provider. MISTR can help you figure out the best PrEP approach for your situation.
Like anything in healthcare, event-based PrEP has its upsides and downsides. Let’s be real about both.
For most people, daily PrEP is simpler. You take a pill every day and you’re protected – no planning around sex, no tracking doses.
But the 2-1-1 method can be a good fit if you:
Common examples: you’re in a long-distance relationship, you travel for work and know your schedule, or you only have sex a few times a month.
The best PrEP method is the one you’ll actually stick with. Both daily and on-demand PrEP work well when used correctly. A provider can help you decide which fits your life.
Interested in on-demand PrEP? Talk to MISTR to find out if the 2-1-1
method is right for you.
The basic 2-1-1 schedule is simple, but real life isn’t always simple. Here’s how to handle common situations:
Scenario 1: You have sex again the next day
Keep taking one pill every 24 hours. Continue until 48 hours have passed since your last
sexual encounter, then stop. You’re extending the protection window.
Scenario 2: You have sex multiple days in a row
Same rule – take your initial 2 pills before the first time, then keep taking 1 pill every 24
hours. Your last pill should be 48 hours after your last sexual encounter.
Scenario 3: You didn’t take the 2 pills beforehand
If you didn’t take the initial 2-pill dose at least 2 hours before sex, you were not protected
for that encounter. Take the 2 pills as soon as possible after and continue with the 1+1
follow-up doses, but understand that protection for that specific encounter is not
guaranteed. Talk to your provider about whether PEP (post-exposure prophylaxis) might
be appropriate.
Scenario 4: You want to switch from daily PrEP to 2-1-1
Talk to your provider first. You’ll need to make sure you’re on Truvada (not Descovy), and
your provider can help you time the transition so you stay protected.
Scenario 5: Can I take 2 PrEP pills in one day?
Yes – but only as the initial dose of the 2-1-1 method, taken 2-24 hours before sex. Do not
take 2 pills as a daily dose. If you’re on daily PrEP, take 1 pill per day as prescribed.
Daily PrEP:
On-Demand PrEP (2-1-1):
Both methods protect against HIV. The right choice depends on how often you have sex,
how predictable your schedule is, and what medication you’re on. MISTR can
help you decide.
1. Can I switch between daily PrEP and the 2-1-1 rule?
Yes, but talk to your provider first. You’ll need to be on Truvada (not Descovy) for 2-1-1 to
work, and the timing of the switch matters to make sure you stay protected.
2. What if I have sex again before I finish the 2-1-1 cycle?
Keep taking one pill every 24 hours until 48 hours have passed since your last sexual
encounter. You’re extending the protection window by continuing daily doses.
3. Is the 2-1-1 rule as effective as daily PrEP?
The 2-1-1 method is about 86% effective for cisgender men who have sex with men
(IPERGAY study). Daily PrEP is over 99% effective when taken consistently. Both work
well, but daily PrEP has a higher effectiveness rate and works for all populations.
4. Do I still need to use condoms with the 2-1-1 method?
PrEP only protects against HIV, not other STIs. Condoms provide broader protection
against chlamydia, gonorrhea, syphilis, and other infections. You can also ask your
provider about DoxyPEP for additional bacterial STI prevention.
5. Where can I get started with PrEP?
MISTR offers free online PrEP consultations. A provider can help you decide between
daily and on-demand PrEP, prescribe your medication, and get it delivered to your door.
You can also review the CDC’s PrEP guidelines for background information.
6. Does the 2-1-1 rule work with Descovy?
No. The 2-1-1 on-demand method has only been studied and proven effective with
Truvada (tenofovir disoproxil fumarate/emtricitabine). Descovy has not been validated for
event-based dosing. If you’re on Descovy and want to try on-demand PrEP, talk to your
provider about switching to Truvada.
7. Can I take 2 PrEP pills in one day?
Only as the initial dose of the 2-1-1 method – you take 2 Truvada pills together, 2 to 24
hours before sex. This is not the same as doubling up on daily PrEP. If you’re on a daily
regimen, take 1 pill per day as prescribed.
8. What if I didn’t take the 2 pills before sex?
If you didn’t take the initial 2-pill dose at least 2 hours before sex, you were not fully protected for that encounter. Take the 2 pills as soon as possible and continue with the follow-up doses, but talk to your provider about whether PEP (post-exposure prophylaxis
for HIV) might be needed.
9. Is on-demand PrEP recommended for women?
No. The CDC does not recommend the 2-1-1 method for people with vaginal exposure to
HIV. PrEP medications take longer to build up to protective levels in vaginal tissue, so
daily dosing is necessary. Women should use daily oral PrEP or injectable PrEP (CAB-
LA).
