How does PrEP work?
When you take PrEP correctly, it stops HIV from entering your cells and replicating (making copies of itself). This protects you against getting the virus.
How long does it take to work?
For daily dosing, you'll need to take PrEP for 7 days before you're protected if you're going to have vaginal/frontal sex, or anal sex.
For on-demand dosing for anal sex:
- take 2 tablets between 2 and 24 hours before having anal sex
- take 1 tablet 24 hours later
- take 1 tablet 24 hours after that
If you're continuing to have sex over a period of time, carry on taking 1 pill every 24 hours until you have not had sex for 2 days.
Are there any long-term side effects?
PrEP can sometimes affect how well your kidneys work. This is why you'll have kidney tests before and during treatment.
PrEP can also affect your bone health, particularly if you have bone mass density (BMD) loss, but this is rare. The risk also stops once you stop taking PrEP.
What will happen if I stop taking it?
If you stop taking PrEP you will no longer be protected from HIV.
If your HIV risk changes, you can stop or restart PrEP, or change the way you take it. Discuss any planned changes with your clinic.
Will I lose or put on weight?
How well does it work?
Daily PrEP is around 99% effective when taken correctly.
On-demand PrEP is also very effective if taken correctly but it has only been studied in gay and bisexual men.
Will it affect my contraception?
PrEP does not affect any type of contraception, including the combined pill or emergency contraception.
However, if PrEP is not working for you and you're being sick (vomit) or have severe diarrhoea for more than 24 hours, your contraceptive pills may not protect you from pregnancy. Check the pill packet to find out what to do.
Find out more:
Can I drive or ride a bike?
PrEP can make you feel dizzy for the first few weeks of taking it. Do not drive a car, ride a bike or use tools or machinery if this happens to you.
It's an offence to drive a car if your ability to drive safely is affected. It's your responsibility to decide if it's safe to drive. If you're in any doubt, do not drive.
Talk to your doctor if you're unsure whether it's safe for you to drive while taking PrEP. GOV.UK has more information on the law on drugs and driving.
Can I drink alcohol with it?
Yes, you can drink alcohol while taking PrEP.
Is there any food or drink I need to avoid?
You can eat and drink normally while taking PrEP.
Will recreational drugs affect PrEP?
Taking PrEP can make recreational drugs work in a different way, especially if you have just started your treatment.
When you start taking PrEP, your body is still getting used to it, so taking recreational drugs at the same time can increase the risk of side effects.
If you are using recreational drugs, tell your clinic doctor as they can explain the risks.
Find out more about the side effects of some recreational drugs on the Frank website.