Disclaimer: This is general health information only and is not a substitute for advice from your GP or healthcare professional.
1. What is HIV PrEP?
HIV PrEP, or pre-exposure prophylaxis, is a medication taken by people who are HIV negative to significantly reduce their risk of acquiring HIV. When taken as prescribed, PrEP is one of the most effective tools available for HIV prevention and works in a similar preventive way to how malaria tablets prevent malaria or how the contraceptive pill prevents pregnancy.
2. How does PrEP work?
PrEP works by blocking an enzyme called reverse transcriptase, which HIV needs to make copies of itself. If exposure occurs through semen, vaginal fluid, or blood, the medication prevents the virus from establishing a permanent infection in the body. For PrEP to be effective, the drug must reach sufficient levels in the bloodstream and relevant tissues before exposure.
3. Who should consider taking PrEP?
PrEP is recommended for people at substantial risk of HIV. This includes people with an HIV-positive partner, particularly if the partner has a detectable or unknown viral load, individuals who have condomless sex with partners of unknown HIV status, men who have sex with men, transgender people, people who inject drugs, and anyone who has recently required PEP or been diagnosed with a rectal or syphilis sexually transmitted infection.
4. How effective is PrEP?
As of 2026, clinical evidence shows that daily oral PrEP reduces the risk of HIV from sexual exposure by about 99% when taken consistently. Long-acting injectable PrEP using cabotegravir, given every two months, has been shown to be even more effective than daily tablets in real-world settings because adherence is easier. New six-monthly injectable PrEP using lenacapavir has shown near 100% effectiveness in clinical trials for people who receive the injection twice per year.
5. How is PrEP taken?
There are three main ways to use PrEP. It can be taken as a daily oral tablet at the same time each day. It can be taken as on-demand or event-based dosing using the 2-1-1 method, which involves taking two tablets 2 to 24 hours before sex, one tablet 24 hours later, and one tablet 48 hours later, noting that this method is currently only validated for cisgender men who have sex with men. PrEP can also be taken as a long-acting injectable given by a clinician every two months or every six months, depending on the medication used.
6. Is PrEP safe?
PrEP is very safe for most people. Around one in ten users may experience mild start-up symptoms such as nausea, bloating, or headache, which usually resolve within two to four weeks. People using oral PrEP require regular blood tests every three to six months to monitor kidney function, while those using injectable PrEP are monitored during routine follow-up visits.
7. Does PrEP protect against other sexually transmitted infections?
No, PrEP only protects against HIV. It does not prevent other sexually transmitted infections such as syphilis, gonorrhoea, chlamydia, or mpox. For this reason, PrEP is best used as part of a broader prevention strategy that includes condoms and regular STI screening, often referred to as a “PrEP-Plus” approach.
8. When should I see a doctor about PrEP?
You should see a doctor if you feel your current HIV prevention strategy is not meeting your needs or if your level of risk changes. A doctor will confirm that you are HIV negative before starting PrEP, check your kidney function, and screen for conditions such as hepatitis B. PrEP should not be started without medical assessment and testing.
9. Can PrEP be stopped and restarted?
Yes, PrEP can be stopped during periods of low or no sexual risk and restarted when risk increases, sometimes referred to as seasonal or holiday PrEP. It is important to continue PrEP for a period after the last possible exposure, usually between 7 and 28 days depending on the type of PrEP and sexual activity, and stopping or restarting should always be discussed with a doctor to ensure full protection.
10. What are the possible complications or risks of PrEP?
Serious complications are rare. A small number of people may experience slight changes in kidney function or bone mineral density with oral PrEP, which usually return to normal after stopping the medication. The most significant risk is the development of drug resistance if PrEP is started while a person already has undiagnosed HIV infection, which is why confirming HIV-negative status before starting PrEP is essential.