There are four different ways someone can take PrEP. The method they use will largely depend on how and when they plan to have sex.

Currently, the only licensed method of taking Truvada is as a daily treatment. A patient can take it in the other ways described below, but in such cases a doctor will need to prescribe it ‘off-label’.

If you’re unsure about the best way to take it, ask your doctor.

On this page, we’ll explain the different ways of taking Truvada, including:

and to which cases each is most suited.

Daily use

This method involves taking Truvada once daily, at the same time each day; however, if you’re a couple of hours early or late taking your tablet, it won’t make it any less effective.

People who engage in vaginal or anal sex can use this method.

The ‘lead-in’ time for daily use is one week, which means that the medicine will reach its optimum effectiveness after you’ve been taking it for seven days continuously.

You should therefore wait until you have been taking PrEP for seven days before engaging in sexual intercourse which may put you at risk.

The daily use method has the highest rate of effectiveness in studies. Taking PrEP on six days a week is the minimum requirement to be protected from transmission occurring through vaginal sex. So, if you are advised to take PrEP daily but miss the odd pill occasionally, you should still be protected.

T’s and S’s

T’s and S’s refers to the days of the week beginning with either T or S; so someone taking PrEP using this method would take one tablet on:

  • Tuesday
  • Thursday
  • Saturday
  • and Sunday

(Which is a total of four times per week.)

During the first week of treatment, it’s still recommended that you take one tablet each day, then drop to taking it on just the T’s and S’s on the second week.

This way of taking PrEP is suitable for people engaging in anal sex (MSM), but not for people engaging in vaginal sex.

It’s thought that this method offers a good base level of protection, and is almost (but not quite) as effective as daily use. So, it might be preferable for people who plan to engage in sexual intercourse less often (for example once or twice per month).

Another benefit of this method is that, for people who are having sex less often, it offers a good level of protection at a lower overall cost (following the lead-in period, you’ll be taking 16 tablets every four weeks, as opposed to 28, so won’t have to order as many tablets).

If you anticipate that you’re going to be having sex more often, you can increase the dose to daily use.


This is sometimes referred to as event-based dosing (or EBD).

It isn’t suitable for vaginal sex, but might be considered by men who anticipate in engaging in anal sex, without a condom, a day in advance:

  • take two tablets between 2 and 24 hours before you plan to have sex
  • take another tablet 24 hours after this
  • and then another tablet again 24 hours later
  • and, if you plan to continue having condomless sex, continue to take the tablet every 24 hours until you go for two full days without sex.

People who have hepatitis B shouldn’t use this method, because stopping and starting the treatment can cause peaks in disease activity (and, in turn, liver problems).

Only one study exists on the use of EBD, so it isn’t as established as the other methods listed here.


Another name for the 7-7-7 method is ‘Holiday PrEP.’

It might be considered for use by those who plan to engage in either vaginal or anal sex, who anticipate:

  • being in an environment (such as a foreign country) where HIV is more common;
  • engaging with one or more casual sexual partners whose HIV status is not known;
  • using substances which might make them less likely to practice sex safely.

This method involves:

  • taking one tablet per day for the 7 days before the higher risk period
  • continuing to take one tablet per day during the higher risk period (so for as long as you’re abroad, for example)
  • and then taking one tablet per day for the 7 days after the higher risk (so, for example, after you return home).

The week-long lead-in period enables the drug to get up to optimum effectiveness before the higher risk period.

Page last reviewed:  06/07/2018