How to take PrEP
This section discusses different ways that you can take PrEP.
PrEP is likely to be most effective when both PrEP drugs are at protective levels before you have sex. However, any PrEP, even if late, is better than none.
Drug absorption and dosing options
Your body takes time to absorb drugs. Therefore, PrEP should be taken both BEFORE sex (to let the levels build up) and AFTER sex (to keep levels high).
Also, each drug is different. FTC is absorbed rapidly, giving protection within hours, but levels drop more quickly. However, TD takes up to 24 hours to reach rectal and genital tissue, but it then stays at higher levels for longer.
TAF is absorbed more quickly that TD and it stays at higher concentrations for longer. However, unless you need TAF for medical reasons, TD is just as effective so long as it is taken as prescribed. TAF is not currently approved in the UK and EU. Approval in the US in only for men and transgender women because none of the first studies included women.
You can take PrEP in different ways depending on your circumstances and how often you have sex.
Women and trans men who want protection from vaginal or front hole sex, need to take daily PrEP at least six days each week. It also takes about a week to reach protective drug levels. This is because PrEP is absorbed differently in vaginal tissue compared to rectal tissue.
On-demand dosing is very effective for anal sex or for straight men having vaginal sex. This involves taking two pills 2 to 24 hours before sex as a double dose. Then a single pill 24 hours and 48 hours after the first double dose (see pages 17 to 19).
On-demand dosing is NOT suitable for women or transgender women having vaginal sex. On-demand dosing is NOT suitable for transgender men for vaginal or front hole sex. In all these cases, the longer lead in of seven days is needed to reach protective levels.
For men whose only risk is insertive sex (vaginal or anal), on-demand dosing is almost certainly okay.
Please talk to your doctor about the best dose and timing that will be most suitable for you.
Last updated: 1 June 2021.