Taking your medicines

PEP emergency medicines for exposure to HIV

You must start treatment within 72 hours (3 days) of possible exposure. After this time, it becomes much less effective. We do not usually recommend starting treatment after 3 days.

Ideally, you should start the treatment within 24 hours of exposure. 

You should start taking PEP immediately after getting your supply.

You should take your medicines for 4 weeks (28 days).

You may get a ‘starter pack’. This means you need to make an appointment to get the rest of the 4-week supply. 

How to take your medicines

Take 1 tablet immediately, as soon as you get your pack.

Then take 1 tablet once a day (every 24 hours).

You should take your tablets with food (a snack or a meal). This prevents you from feeling sick.

Each tablet contains emtricitabine 200g and tenofovir disoproxil 245mg.

Take 1 tablet immediately, as soon as you get your pack.

Then take 1 tablet twice a day (1 in the morning and 1 in the evening). They should be as close to 12 hours apart as possible (for example, at 9am and 9pm).

You can take the tablets with or without food. Taking them with food could prevent you from feeling sick.

You need to swallow the tablets whole. Please do not crush, chew or split them as this can affect the levels of medicine in your body.

Each tablet contains raltegravir 400mg.

You can take one of your raltegravir tablets at the same time as your emtricitabine / tenofovir disoproxil tablet. 

You could space out the medicines as follows:

9am Take 1 emtricitabine / tenofovir disoproxil tablet and 1 raltegravir tablet together, with breakfast
9pm Take 1 more raltegravir tablet before bed

We may give you different medicines if the person you had contact with is HIV positive and has a resistant strain of HIV (also called a resistant virus). Other medicines may work better in this situation. 

We give you more information about each medicine that we prescribe for you.


Missing a dose 

It's important that you do not miss any doses. You should take the medicines regularly to make sure the level of medicines in your blood is constant.

If you do miss a dose, take it as soon as you remember. You should take your next dose at its regular time.

If it is almost time for your next dose, do not take a double dose. Wait and take the next dose at the regular time. 

If you have not taken any of your treatment for 48 hours, tell your doctor as soon as possible.

Taking other medicines with PEP

The medicines in your pack might not mix with other medicines. 

Tell the doctor caring for you about any medicines you take. This includes medicines you buy (from a pharmacy or shop) and herbal remedies.

After starting PEP, you should always tell anyone who recommends a new treatment that you take these medicines. 

Always check with a doctor or pharmacist before starting any new medicines during the 28 days of treatment.

Some vitamins and minerals, such as those in indigestion remedies, can stop you from taking in raltegravir properly. They include:

  • calcium
  • iron
  • magnesium
  • aluminium

You should not take these at the same time as raltegravir, but can take them 4 hours before or afterwards.

Unlicensed medicines

PEP medicines are officially approved (licensed) for treating HIV, but not for preventing it. However, the Department of Health recommends using them if you might have been exposed to HIV. The medicines could help to reduce the risk of you getting HIV infection.

Read our information about taking unlicensed medicines.

Resource number: 3983
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Contact us

Phone: 020 7188 7707

For medical students on electives abroad:

Contact the occupational health department.

In an emergency, phone 020 7848 6490 or email [email protected] 

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Contact our Patient Advice and Liaison Service (PALS)

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