On-demand PrEP (2-1-1)

On-demand PrEP, or the 2-1-1 schedule, means taking PrEP only around the time of sex. Learn how to take it, who it suits and does not, its effectiveness, and cautions.

What on-demand PrEP is

On-demand PrEP, also called event-driven PrEP, means taking PrEP only around the time you expect to have sex, instead of every day.

Different from daily PrEP

Rather than taking a pill every day all the time, on-demand PrEP is taken as a short course around a period of risk, following a clear schedule called 2-1-1.

It suits some groups

On-demand PrEP suits people who have sex less often and can plan ahead. However, there are limits on who can use it. See the full PrEP overview at what is PrEP.

The 2-1-1 schedule

The 2-1-1 schedule is the accepted way to take on-demand PrEP, and it has three timing points.

How to take it for one occasion

• 2 pills taken 2 to 24 hours before sex
• 1 pill 24 hours after the first dose
• 1 pill 24 hours after the second dose

That is 4 pills in total for one occasion, with each dose about 24 hours apart.

The pre-sex dose matters most

The double dose before sex is the most important part for protection, so plan to take it at least 2 hours ahead, giving the drug time to reach a high enough level.

An easy way to remember 2-1-1

The numbers 2-1-1 make it easy to remember: 2 pills before, then 1 pill, then 1 more. Remembering this pattern helps you take it correctly each time.

If sex continues over several days

If sex continues over several days, the schedule adjusts slightly.

Keep taking it until the end

If you have sex several times over a few days, keep taking one pill a day for as long as sex continues, and carry on for 2 more days after the last time.

No need to restart the count

You do not need to start a new double dose each time if you are already taking it continuously — just take one pill a day until 2 days after the last sex. Understanding this helps you use it correctly.

An example

For example, if you have sex on Friday, take 2 pills at least 2 hours before, then 1 pill on Saturday and 1 on Sunday. If you also have sex on Saturday, keep taking one pill a day until 2 days after the last time.

How effective it is

On-demand PrEP has evidence that it works well in the groups studied.

Evidence from research

The IPERGAY study in men who have sex with men found that the 2-1-1 schedule significantly reduced the risk of getting HIV, and the World Health Organization recognises it as an option for PrEP.

It depends on taking it correctly

Like daily PrEP, the effectiveness of on-demand depends on following the schedule closely, especially the pre-sex dose. Done correctly, it gives good protection.

Who it suits

On-demand PrEP suits some groups more than others.

It suits people who

• are men who have sex with men, the group with the clearest evidence
• have sex infrequently or can predict it in advance
• find a daily pill inconvenient or unwanted
• have periods without sex

You must be able to plan

Because the pre-sex dose matters so much, people using on-demand should be able to plan or anticipate the time of sex in advance. See who PrEP suits at who should take PrEP.

Who should not use it

An important thing to understand is that on-demand PrEP is not right for everyone, and some groups should use daily PrEP instead.

Not yet recommended for

• people who have vaginal sex, including women, because there is not yet evidence that the 2-1-1 schedule works — daily dosing is the only proven method for this group
• people with hepatitis B, because stopping and starting can affect the liver
• people who share injecting equipment, as there is not enough evidence

Always consult first

If you are in one of these groups or are unsure, talk to a provider first, who can advise whether daily or another option suits you better.

Safety first

Knowing which groups should not use on-demand is as important as knowing how to take it, because using it in the wrong group can leave protection incomplete. Talking to a provider helps you choose safely.

Advantages versus daily

On-demand PrEP has some advantages over daily PrEP for the right people.

The advantages

• fewer pills for people who have sex infrequently
• flexible, fitting a lifestyle with occasional sex
• less burden than a daily pill

But it means planning

These advantages come with the need to plan and follow the schedule closely. For people who have sex often or cannot predict it, daily PrEP may be more convenient and reassuring.

Choose what fits your life

Choosing between on-demand and daily depends on your lifestyle and risk, and neither is better overall — only one that fits you better.

Cautions and limitations

There are important cautions to know before choosing on-demand PrEP.

Limits to be aware of

• only works with certain medicines — the 2-1-1 schedule has evidence only for particular antiretrovirals, not all of them, and not the injectable
• must be taken exactly as scheduled, especially the pre-sex dose
• needs planning in advance — for unexpected sex, there may not be time to protect yourself

When unsure, ask

If you are not sure whether on-demand suits you, talk to a provider, who can help choose the safest and most suitable method.

Always ask

If you have questions about the on-demand schedule, timing, or whether it suits you, do not hesitate to ask a provider. Understanding it clearly before use helps you protect yourself with confidence.

On-demand does not protect against other STIs

Like all forms of PrEP, on-demand only protects against HIV.

It does not cover other infections

On-demand PrEP does not protect against other STIs, such as syphilis, gonorrhoea, or pregnancy, just like daily PrEP.

Use it with condoms

Using condoms as well protects against other infections and pregnancy, and regular sexual-health check-ups matter too, making your protection more complete.

Consult before starting

Before starting on-demand PrEP, talk to a provider for safety and effectiveness.

Before starting

• you must test for HIV first and be negative
• a provider will assess whether on-demand suits you or whether another option is better
• there are baseline checks and a follow-up plan

Get the right guidance

Because the on-demand schedule has specific details and limits, getting guidance from a provider helps you use it correctly and safely. See how to get PrEP at where to get PrEP and how much it costs.

In summary

On-demand PrEP, or the 2-1-1 schedule, means taking PrEP only around the time of sex — 2 pills 2 to 24 hours before, then 1 pill at 24 hours and 1 pill at 48 hours. It is an option with evidence in men who have sex with men.

On-demand suits people who have sex infrequently and can plan, but it is not yet recommended for people who have vaginal sex, people with hepatitis B, and some other groups, so talk to a provider first. And like all forms of PrEP, use condoms as well to protect against other infections.

If you are interested in on-demand PrEP or want to start, find and book a clinic at Love2Test.