What is PrEP?


Pre-exposure prophylaxis, popularly known as PrEP for its acronym in English, is an HIV prevention strategy that consists of taking a medication against the virus (antiretrovirals) before being potentially exposed to it, to avoid the probability of infection.


For whom is it indicated?

PrEP is a preventive method indicated for HIV-negative people who, due to their personal situation or at certain times, may have a high probability of acquiring HIV.




You might consider taking PrEP if …

… you are a man who has sex with men (homosexual, bisexual or other men who have sex with men) or a transsexual woman, 18 years or older and at least you meet two of the following requirements during last year:

Having had more than 10 different sexual partners

Having had condomless anal sex

Having used drugs in the context of unprotected sex

Having taken post-exposure prophylaxis (PEP) on several occasions

Having had at least one bacterial STI


PrEP is not for you if …

… you already have HIV, because the medication used for PrEP is not effective in treating the infection.

In case you have kidney failure or some pathology that can affect the kidney such as diabetes or hypertension, you can take PrEP, but it will be necessary for a doctor to monitor you more regularly. However, in some more severe cases, PrEP may be discouraged.


How does it work?

The medication used for PrEP combines two active ingredients (emtricitabine and tenofovir) that work by blocking an element of HIV that allows it to infect cells and replicate. Therefore, the person taking PrEP is able to block HIV infection, even if his body has been in contact with the virus.



How effective is it?

Various studies, both national and international, have shown that PrEP is highly effective – it offers close to 100% protection – as long as it is taken following prescription guidelines.


Does it have side effects?

The drugs used for PrEP are very safe and have a low toxicity profile. However, it is advisable that a specialized doctor prescribes them and that the PrEP user undergoes regular medical checks to ensure adequate follow-up.


What adverse effects can I have if I take PrEP?

Although most users of PrEP do not experience any and if they appear they are usually mild (such as a hangover or poor digestion), the most common adverse effects of the treatment are the following:

Hypophosphatemia (low level of phosphorus in the blood): headache, dizziness, diarrhea, vomiting, rash, weakness … These can appear in less than 1 in 10 cases during the first days of taking PrEP and disappear afterwards a few days or shortly after starting treatment.

Impaired kidney function (abnormal kidney function). It occurs in less than 1 in 100 cases and is usually not significant. However, it is advisable to have periodic reviews of kidney function to detect it early.

Decrease in bone mineral density (lower presence of calcium and other minerals in the bones). It can occur during the first months of taking PrEP, but it is an effect that disappears when the medication is stopped and that can be reversed by doing physical activity, following a balanced diet, and with exposure to sunlight. It must be said, however, that this decrease in bone density is not significant and does not represent any risk in people without a severe history of osteoporosis.




Do you have to take it every day?

To begin with, it must be clarified that PrEP is not a vaccine. Therefore, the protective effect against HIV is only maintained while taking the medication.

Depending on your needs and in accordance with GESIDA’s recommendations, you can choose between two different regimens:


1-Daily regimen

If you decide to take PrEP on a daily basis, you should take one pill each day of the week at the same time.

Pauta Diaria

Although with the fourth dose taken continuously PrEP already provides some protection it is from the seventh that the maximum level is acquired. Therefore, a week after starting the treatment and as long as you continue taking it, you will be protected at any time.

The daily regimen is the most common way to take PrEP and the one that is generally recommended to everyone.


2-On demand

If you only want to take PrEP during periods of sexual activity or when you think you are more exposed to HIV, you can choose this regimen.

A demanda

In this case, you should take two tablets together 12 hours before having sex. If you cannot meet this deadline, take two tablets at least 2 hours before intercourse. You will have to take the third tablet 24 hours after the previous ones and the next day you will have to take another. In total, you will need to take four tablets and always do it approximately at the same time.

In case you have intercourse two or more days in a row, you should take an additional tablet for each day that you want to remain protected and take the last 48 hours after the last intercourse.

A demanda 2


VERY IMPORTANT! On-demand PrEP only works for men. Due to their physiological characteristics, cisgender and transgender women who take PrEP must always follow the daily regimen to ensure optimal drug concentrations in the blood.




Does it protect against other STIs?

No, PrEP does not protect against other STIs (syphilis, chlamydia, gonorrhea …). However, since people who take PrEP undergo quarterly STI controls, this allows early diagnosis and treatment of these types of infections even if they are asymptomatic.

On the other hand, PrEP can be combined with other preventive methods such as the condom, in order to reduce the possibility of contracting STIs, especially in anal sex.



PrEP has been incorporated into our health system since November 1, 2019. From that moment on, it can be accessed, at no cost to the user, by people who are considered to be at higher risk of contracting HIV.

BCN PrEP·Point is one of the 19 centers authorized by the Generalitat de Catalunya for the prescription, dispensing and monitoring of PrEP with funding from the public health system. To access it, see the Access to PrEP section.




What should you do before starting PrEP?

A medical check-up for …

Getting tested for HIV to find out your HIV status

Getting tested for other STIs (hepatitis A, B, and C, syphilis, chlamydia, and gonorrhea)

Getting vaccinated against hepatitis A and B, if applicable

Taking a blood test to know your health condition in general and, especially, if you have a good kidney function

and also…

Ask yourself if you will be able to take the medication constantly and have regular check-ups


What will you have to do while taking PrEP?

You will need to take an HIV test every 3 months to confirm that you have not acquired the infection. Periodically, you will also have to undergo controls for other STIs and the correct functioning of the kidney.




What is the best way to preserve it?

PrEP should be stored at room temperature and in a dry place. Therefore, neither the refrigerator nor the interior of a car is a suitable place. It is recommended to keep the tablets in the original bottle that protects them from moisture.


What can you do to remember to take your pills at the right time?

There are a few ways that can help you follow the PrEP schedule correctly:

-Associate taking PrEP with another activity that you do every day at the same time: at breakfast, before brushing your teeth or together with other medications that you might take daily.

– Put the medicine bottle in a visible place.

-Set an alarm every day at the same time or write it down in your phone’s agenda.

-Use one of the mobile phone applications specifically designed to remind you to take medications.


What do you have to do if you have forgotten to take a dose?

If you follow the daily guideline and you realize that you have forgotten to take it and it has not yet been 12 hours, you can take it then.

If you find out that you forgot to take your pill the next day, you don’t need to take two tablets to make it up.

If you are not sure if you have taken it today, do so. Taking two tablets on the same day from time to time is safe

If you take PrEP daily you should keep in mind that even if you skip your dose once or twice a month, you still have a high level of protection. However, if you forget often, we recommend that you look for strategies that help you follow the regimen properly so as not to compromise your health.

If you use the on-demand schedule and forget to take one of the tablets, take it as soon as possible. If you realize it the next day, it is advisable that you go to the emergency services of a hospital for PEP because you may not be sufficiently protected.


What can you do if you experience adverse effects?

To minimize the risk of stomach-related side effects, nausea or dizziness, it is advisable to take the tablet with food or at night, just before going to sleep. In any case, these discomforts usually disappear within a week after starting treatment.


What should you do if you want to stop PrEP?

If you consider that you no longer need PrEP, because your level of exposure to HIV has decreased, you can stop taking the medication but you will need to continue taking a tablet for at least two consecutive days after the last relationship (in case you are a man) or seven consecutive days (in case you are a woman).

If you want to resume treatment, remember that you will not be fully protected until you have been taking one tablet every day for a week. In case of men, you can also choose to take two tablets together at least two hours before intercourse.