PrEP
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Medically reviewed by
Dr Daniel Atkinson
GP Clinical Lead
on June 13, 2023.
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Different ways of taking PrEP

PrEP medicine is available as an oral tablet, which can be taken in a few different ways and situations where you might be exposed to HIV. 

One situation is when you are sexually active and you want protection from HIV from new or prospective partners who could potentially be HIV positive. So you take PrEP as and when you need it. Or it could be you’re in a relationship where your partner is HIV-positive but you aren’t. To avoid contracting the virus in that case, it’s better to take a daily tablet.

Taking PrEP medication will reduce your chances of being infected by HIV. But it’s good to know about the other ways you can stay protected, such as using condoms and not sharing needles. Condoms provide a barrier against STIs, so combining them with PrEP helps to strengthen your protection and lowers your risk of infection. 

Studies of PrEP have shown it to be an effective way of preventing HIV. Not only does the medication stop you from getting infected, but it can also make your relationship more stable as you may experience stronger feelings of intimacy and trust.

Some people who regularly use PrEP have said they feel empowered, gaining control of their own HIV protection. Taking responsible actions for preventing HIV can build trust, putting both you and your partner’s minds at ease about transmission risks.  

Taking PrEP daily

If your lifestyle carries regular HIV infection risks, a clinician might recommend taking PrEP daily. This will mean you’re protected all the time.

Daily PrEP is for anyone who wants constant, effective protection from HIV. If you’re sexually active and your exposure to the virus is frequent or unpredictable, this is probably the best option for you. You can sometimes get PrEP on the NHS, but it involves an appointment at a specialist sexual health clinic rather than your GP.

PrEP tablets contain two active ingredients, emtricitabine and tenofovir. Both are antiviral drugs that work together to stop HIV from multiplying in your body. By taking it every 24 hours, the drug stays in your system all the time. Clinical trials have suggested this method to be around 99% effective at preventing HIV.

Taking PrEP at the same time each day makes you more likely to develop a schedule you know you’ll stick to. It also lowers the risk of being infected if you find yourself in an unpredictable situation where you’re unsure about exposure to HIV. Keeping the tablets in a safe place close to hand or setting an alarm can get you into a proper routine that will make sure the medication is as effective as possible.

Taking PrEP on-demand

Another way of taking PrEP is on-demand, which is sometimes called event-based-dosing (EBD). This is a more casual way of taking the medicine, and whether it’s right for you depends a lot on when you’re planning to have sex.

Possibly the most important thing to know about using PrEP this way is that it only offers protection for receptive anal sex. Taking the medication on-demand is equally as effective against contracting HIV, but if you’re planning on having vaginal (frontal) sex or are using injected drugs with someone who might have the virus, you’d need to be on a daily PrEP routine for full protection.

How the medication is taken on-demand differs from using it daily, too. For the drugs to work properly, you’ll need to follow a specific pattern.

  • 24 hours before you know you’ll be having unprotected sex (or potentially becoming exposed to HIV), take 2 pills.
  • Take another pill 24 hours later.
  • After another 24 hours after that, take your last pill.

If it sounds like a lot to take in, the schedule can be remembered as 2-1-1.

The routine will again need to change slightly if you’re planning on having more than one ‘event’ that puts you at risk of exposure, such as a weekend or any situation where you might have sex on continuous days. In this event, you’ll need to carry on taking a PrEP tablet for each day that the activity continues. After the last time you’ve had sex, you’ll take a tablet every 24 hours for two more days.

However, if you have an active hepatitis B infection, PrEP drugs can be a problem. The drugs in PrEP also suppress hepatitis B virus, so taking the tablets in a stop-start fashion can cause flare-ups that lead to liver complications. So if you have hepatitis B, talk to your clinician before taking PrEP this way.

Are there any other ways PrEP can be taken?

There are other ways PrEP is used that might be more appealing if you’re looking for flexibility.

  • Holiday PrEP — This method involves taking PrEP for a block of time, when your risk of HIV exposure is higher. It can be used for vaginal and anal sex. This might be a good option if condoms aren’t at your disposal, or you’re potentially going to be in a situation where drugs are being used.

The pattern for taking your tablets would be 7-7-7: one tablet per day a week before the holiday, one per day for the week you’re sexually active, and one a day for a week after the last time you have sex.

  • 4 pills a week, aka ‘the Ts and Ss’ — This method should only be used for anal sex (because that’s the way it's been tried and found to be effective). The name comes from the pattern you take the tablets: Tuesday, Thursday, Saturday and Sunday. This method is good for when you don’t know when you’re having sex.

It’s important to know that the studies and clinical trials that measured how effective these methods are were done on fairly small populations. Our clinical team have looked at the research and are happy to prescribe PrEP in the ways described above because the benefits of preventing HIV infections outweigh the potential risks. It’s always best to be fully informed about your HIV risks so you have a clear picture of which tablet routine will give you the best protection.

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How long does it take for PrEP to work

For anal sex it will take at least seven days of daily PrEP use for it to reach its full effectiveness. But for vaginal sex or drug use, it will take a full 21 days.

It’s best to stick to a daily schedule when taking PrEP as consistency is important in its effectiveness. However, if you’re taking on-demand PrEP then make sure you follow the guidelines correctly and take the doses at the right time.

If you accidentally missed a dose the effectiveness of PrEP might have been reduced, especially if you’ve missed more than one dose. In this case, it’s best to use an extra form of protection, such as condoms to prevent the risk of getting HIV.

Forgetting to take your PrEP

You should always use PrEP as prescribed to you by a clinician. With lots of other treatments, it might not matter too much if you miss a dose, but with PrEP it does – if you skip a dose or forget to take it, your protection against HIV will be lower.

If you’re taking daily PrEP tablets and forget a dose, take a tablet as soon as you remember. If it’s approaching the time you’re due your next dose, just wait until it’s time for that one and continue your routine as usual. There’s no need to take a double dose to make up for the one you missed.

However, suppose you’re taking event-based PrEP and haven’t taken the required doses before having condomless sex. In that case, you’ll need to take some fast steps to ensure you remain protected, as your chances of contracting HIV will have significantly increased. To get immediate help, go to your nearest A & E department for advice if you think your HIV risk is high. If that’s not an option, speak to a clinician as soon as possible for the best advice on what to do next.

You might be told to take a double dose in this event, or you could be prescribed PEP (post-exposure prophylaxis). PEP is a combination of drugs that can stop HIV developing. These drugs are known as antiretrovirals. It’s usually only prescribed as a last resort, so it’s best to stick to a PrEP routine where it’s unlikely you’ll forget to take a dose. Setting an alarm, or leaving your tablets somewhere you’ll see them (such as a bathroom cabinet) will help with this.

Will I need to take a HIV test?

You must take a HIV test before you start taking PrEP to make sure you don’t have the virus already. The medicines contained in PrEP are also used to treat HIV but are often used in combination with other medicines or at different doses. Taking PrEP if you have HIV without knowing it might make your infection more difficult to treat.

You should also get a full STI screening regularly (ideally every three months) if you’re taking PrEP or at risk of exposure to HIV.

Along with using condoms and being informed about your risks, regular testing is part of the process that ensures you’re protected while taking PrEP. This can be done through your GP, or a sexual health clinic, who might recommend tests you can do at home.

PrEP drugs can affect kidney function for some people too, so regular testing is recommended to make sure you’re healthy overall.

If HIV is left untreated, it can develop into AIDS-related illnesses which can have serious, long-term effects on your health.

Being HIV-positive doesn’t mean you can’t live a normal life, but the impact it has on your immune system means you’ll need to take regular medication to slow the progression of the virus and stop it developing further.

How do I start PrEP?

You can start PrEP treatment as soon as you’ve had a test to make sure you’re HIV negative, and decided it’s the right choice for you.

In the UK, the main type of medication prescribed for anyone looking for protection from HIV is generic PrEP. There is also a branded version, Truvada, which is occasionally used. In the USA, there is another type of PrEP called Descovy available. It was approved for use in 2019, but isn’t available in the UK.

Both daily and on-demand PrEP have been studied and found to prevent the spread of HIV. To begin using it, you’ll need a consultation with a clinician about your current health. You’ll have to take a HIV test before starting a course of tablets. Because tablets can interfere with both kidney function and hepatitis B, you’ll also be asked to test for these along with a full STI screen.

Can you get PrEP on the NHS?

You can get PrEP on the NHS, but it usually involves an in-person appointment at a specialist sexual health clinic rather than seeing your GP. PrEP medications can be prescribed to you by doctors or pharmacist prescribers. So getting your medication online might suit you better if you want to avoid talking about your sexual health face-to-face.

If you’re ordering from any online pharmacy services, it’s always worth checking they are registered with the General Pharmaceutical Council (GPhC), and that doctors hold a GMC (General Medical Council) licence. For extra peace of mind, checking the service is registered with the Care Quality Commission (CQC) means that their practice has been independently inspected and a report has been published on how effective and safe it is.

How long can you take PrEP for?

In theory, there isn’t an upper limit on how long you can take PrEP for. There isn’t a lot of data available at the moment that analyses long term use, but this is mainly because the drugs used in PrEP have only started to be used in a preventative capacity fairly recently.

There is data though on how safe and effective long term use of these drugs are, because they’ve been used to treat HIV for several years – and clinical safety data for long term use doesn’t show any additional risks.

Is PrEP usually for men only?

Persons of any gender can use PrEP. Despite popular stigmas surrounding the spread of HIV, it’s a virus that affects everyone, no matter their gender, race, age or sexual orientation.

PrEP is for anyone who is at risk of contracting HIV. This can be both from unprotected sex, or injected drug use. There are other rarer instances where transmission might occur (such as through open wounds) but they’re generally considered to be little or no risk.

The type of sex you’re having can determine how you take PrEP. On-demand PrEP might be the best option for single heterosexual men and women who are travelling to places with a higher HIV rate. Whereas for couples where one person is HIV-positive a better option would be daily PrEP. This would offer constant protection during your relationship.

PrEP, condoms and HIV

Latex condoms can be used as a barrier from sexually transmitted diseases (STDs) and HIV infection. Transmission occurs when the virus is shared through bodily fluids, such as semen, blood, or vaginal fluids. As well as being easily-accessible on the high-street and in most pharmacies, condoms are easy to carry around with you. Used alongside PrEP they can form part of a routine that will help prevent you contracting it.

While condoms do offer a short term solution, they can potentially split or not work properly. If your risk of exposure to HIV is high, then PrEP might be the best choice for you.

Will I get side-effects while taking PrEP?

care-iconMost people tolerate PrEP well and get very few side effects. Any problems the tablets cause will usually settle down over time.

Nausea, stomach pain, headaches and fatigue are commonly experienced while adjusting to PrEP. It’s safe to use both on-demand and long-term, but you should speak to a clinician if your side effects don’t subside.

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This page was medically reviewed by Dr Daniel Atkinson, GP Clinical Lead on June 13, 2023. Next review due on June 13, 2025.

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