How to Take PrEP

Knowing how to take PrEP, what to do if you miss a dose, and what happens if you stop your treatment can all help you stay safe and protected in the long term.

Different dosing schedules work for different lifestyles. But once you’ve made your decision, taking PrEP as instructed is one of the most effective tools for preventing HIV.

This guide breaks down everything you need to know, from choosing between daily and event-based dosing to switching schedules if your circumstances change.

Three key takeaways

• When you take PrEP daily, it offers up to 99% protection when you stick to your routine.
• Event-based dosing can work brilliantly if you're good at planning ahead. If your sex life tends to be more spontaneous, daily dosing will probably feel much less stressful.
• If you do miss a pill, don't panic, but do act quickly. What you need to do next depends on a few things (your schedule, the type of sex you've had, and timing), and you might need post-exposure prophylaxis (PEP).

What is PrEP?

PrEP is a group of medicines that can reduce your risk of getting HIV by up to 99% when taken properly. It can be taken orally or by injection.

If you want to better understand what PrEP is, our guide explains how it works, what treatments are available, and how you can access it safely.

Daily PrEP

The most effective way to take PrEP is every day. Daily PrEP gives you up to 99% protection, compared to 86-97% with event-based dosing.

Taking PrEP every day is recommended if you have sex frequently or know you might struggle with remembering to take your medication on demand.

The NHS encourages daily PrEP for those who are having vaginal and/or anal sex. To start taking PrEP daily, you should:

1. Take one tablet every day, around the same time each day. It's best to take it with or after food.
2. Wait seven days after you start taking it before you have sex.
3. If you think you may have sex within the first seven days, take two tablets at least two hours before you have sex.

Tip: If you're sick within one hour of taking PrEP, take another tablet. If you're sick more than one hour after taking PrEP, do not take another tablet.

Event-based dosing (EBD)

Often referred to as on-demand dosing, event-based dosing involves you only taking PrEP when you plan to have sex. There are different dosing recommendations depending on what type of sex you’re having.

2:1:1 dosing

A 2:1:1 dosing schedule is recommended if you’re giving vaginal sex or giving/receiving anal sex. You should:

1. Take a double dose of PrEP 2-24 hours before you have sex.
2. Take a single pill 24 hours after the double dose.
3. Take another single pill 24 hours later.

If your sexual encounter is a one-off, then you’ll take a maximum of four tablets.

Important: If you’re having sex multiple times a week, you should keep taking a pill each day you have sex, remembering to still take one pill two days after the last day you have sex.

2:7 dosing

If you’re a cis woman, trans, or non-binary person planning on dosing on-demand, and receiving vaginal sex, then it’s recommended you:

1. Take a double dose of PrEP between 2-24 hours before you have sex.
2. Taking a single pill every 24 hours for the next seven days.

This means you will take nine pills in total.

“The key thing to remember about event-based PrEP is that while it’s flexible, it’s not magic. You should still plan ahead!

“If that’s something you might struggle with, or you know that you’ve got a sex life that is quite spontaneous, it’s better to consider daily dosing instead.

“If you are taking PrEP on demand, then make sure you’re not cutting corners, or skipping those follow-up doses. PrEP is a powerful tool that gives you back your sexual freedom, but it works best when you use it in a way that suits your lifestyle.”

Ness Cooper, Clinical Sexologist

5 tips for taking PrEP safely

However you choose to take PrEP, there are a few things to keep in mind to make sure that you're getting the most out of your treatment. Top tips include:

1. If dosing on demand, take PrEP early enough (2-24 hours before sex) and keep taking it for as long as recommended above, depending on the type of sexual contact. Most people who get HIV when using PrEP got it because they stopped taking it too soon or forgot to take it regularly.
2. If you've stopped PrEP or taken a break, then make sure you get advice from your clinician on how to restart safely.
3. Continue to get STI screenings regularly while you're taking PrEP. It's important to remember that PrEP will only protect you from HIV.
4. Try your best not to miss pills. If you do miss a pill, don't give up just because you were late with the first dose.
5. Regardless of how you choose to take PrEP, you shouldn’t take more than one double dose within seven days.

What to do if you miss a pill

Missing doses of PrEP may mean you’ve got to take PEP (post-exposure prophylaxis)to reduce the risk of becoming HIV positive.

However, the actions you take before this depend on what dosing routine you’ve chosen, and what type of sex you’re having.

For example, if your only risk of exposure has been oral sex, then you won’t need to take PEP regardless of how many doses have been missed.

For daily PrEP

If you're daily dosing, what you do if you miss a dose depends on how long it's been since you were supposed to take it.

If you remember within 12 hours of your usual time:

1. Take your missed pill as soon as possible.
2. Continue taking one tablet every day at your usual time.

If more than 12 hours have passed since your usual time:

1. Skip the missed dose entirely.
2. Take your next dose at your usual time the next day and carry on as normal. The British HIV Association (BHIVA) suggests that it may be recommended to take two tablets for your initial restarting dose, depending on the gap and the number of correctly taken doses in the previous seven days.

You may still be protected as long as you have taken at least four tablets in the previous seven days if you're having anal sex, or at least six tablets in the previous seven days if you're having vaginal or frontal sex.

For event-based dosing

With event-based dosing, there's less medication in your body at any one time, so it's especially important that you take all of your doses on time and don't skip any steps.

If you forget a dose, what you do next depends on which part of the schedule you've missed:

If you missed your double dose before sex:

1. Take both tablets as soon as you can, even if this is after sex.
2. Continue with your single daily doses as normal to complete the course.
3. Contact your clinic or doctor as soon as possible to find out whether you need additional protection from PEP.

If you forget any other dose in your schedule:

1. Take it as soon as you remember.
2. Continue with the rest of your doses at the usual intervals.
3. Contact your clinic or doctor as soon as possible to find out whether you need additional protection from PEP.

Ideally, you should start PEP within 24 hours of having sex, but it can be taken up to 72 hours after.

If you find that you're regularly missing doses, it's worth considering whether daily PrEP might be a better fit for your lifestyle, as it will give you a higher level of protection overall.

Should you take PrEP daily, or on demand?

In most cases, we’d recommend you take PrEP daily, as this will give you the highest level of protection against getting HIV.

However, we understand that in certain circumstances, it might be better to switch from daily to event-based dosing. For example if you’re struggling with certain PrEP side effects.

If you are taking PrEP on-demand and want to switch to daily dosing, you should:

1. Count your medication. You need to make sure you have enough medicine to last until your next appointment, or when you’re next due to place an order privately.
2. Start with a double dose. When stopping, you should take your medicine between 2-24 hours before you plan to have sex.
3. Continue taking PrEP daily, at the same time every day.

If you are taking PrEP daily and want to switch to on-demand dosing, you should speak to your healthcare professional. They will help you make the decision as to whether event-based dosing is an option for you and will help you make the change in your dosing schedule safely.

Stopping PrEP

If you are thinking about stopping PrEP, then the first thing you should do is speak with your healthcare professional. They’re able to give you the necessary advice on preventing HIV and any other STIs, as well as:

• help you stop PrEP safely
• organise any additional tests that you may need

You can always if restart PrEP if you change your mind! Just make sure you speak with your clinician first.

If you have stopped PrEP and are concerned that you might have been exposed to HIV, you might need to take PEP. You should speak to a clinician as soon as possible as you cannot take PEP any later than 72 hours after exposure.

How our team of expert clinicians can help

At Chemist4U, our team of expert clinicians can help you stay on track with your routine by making sure that you always have a steady supply of PrEP.

We offer discreet, next-day delivery, helping you bypass waiting times so you’ll always know you can get your next dose without worry.

Frequently asked questions about how to take PrEP

How many days does it take for PrEP to kick in?

PrEP can give you protection within two hours. When taking it daily, you’ll take a double dose for your first day 2-24 hours before having sex.

When taking it on demand, you should always take PrEP 2-24 hours before you’re planning on having sex.

What happens if I take too many PrEP tablets?

If you take three PrEP tablets or more at the same time, you should contact NHS 111 for advice now.

Do both partners have to take PrEP?

While both sexual partners don't have to take PrEP there are some situations where it is advisable. For example, if both parents are HIV-negative but: they have other sexual partners or are in an open relationship.

Sources

• How and when to take Pre-Exposure Prophylaxis (PrEP). 2023. [Accessed 04/02/2026]
• How to take PrEP. SH:24. [Accessed 04/02/2026]
• British Association for Sexual Health and HIV/British HIV Association guidelines on the use of HIV pre-exposure prophylaxis (PrEP). 2025. [Accessed 19/02/2026]