What is PrEP HIV Prevention and What Are the Side Effects?

What is PrEP HIV Prevention and What Are the Side Effects


What is PrEP?

Pre-exposure prophylaxis, better known as PrEP, is a daily treatment that protects HIV-negative individuals from becoming infected with the virus. Currently, Truvada is the only brand that has been approved for use for pre-exposure prophylaxis. Truvada contains two antiretroviral drugs: tenofovir, a nucleotide analogue drug (a ‘nuke’), and emtricitabine, a nucleoside reverse transcriptase inhibitor (NRTI)

What is This Medication Used For?

PrEP is used by HIV-negative individuals who are at high risk of contracting the virus either through sexual activity or intravenous drug use. Pre-exposure prophylaxis does not provide protection from other sexually transmitted infections (STIs). The combination of the anti-HIV medications provided in PrEP prevents the virus from replicating in the user’s body. This means that if an individual who has been taking PrEP properly is exposed to HIV, there will be high enough levels of the medications in their body that they will be protected from contracting the virus.

When taken daily, studies have shown that PrEP reduces the risk of contracting HIV from sex by approximately 99%. If taken correctly, studies show PrEP reduces the risk of infection by 74% among users who inject drugs. However, pre-exposure prophylaxis is not recommended for everyone.

Pre-exposure prophylaxis should only be used by individuals who:

  • Are in a sexual relationship with a person who is living with HIV, whose HIV is not controlled
  • Are gay or bisexual men with multiple casual sexual partners who do not always use protection
  • Are gay or bisexual men engaging in a sexual relationship with a new partner whose HIV status is unknown, and who are not using condoms
  • Are engaging in a sexually relationship without using condoms, with partners of the opposite sex whose HIV status is unknown but who may be at high risk of infection (i.e. intravenous drug users, or individuals who have multiple partners at once or who engage in sexual activity with bisexual male partners)
  • Have shared injection equipment with other individuals, or who have been in treatment for intravenous drug use

How to Take It

The way you take PrEP depends on whether you are having vaginal or anal sex. For vaginal sex, individuals must take the oral pill once daily for 7 days for it to become effective. This method of daily dosing is also suitable for anal sex as well. It is best to take the pill at the same time every day to make it part of your routine. With this method, it is okay if you miss a pill by accident, as you will still be protected after the initial 7-day window.

The other method of taking PrEP is on demand, or event based. This is only suitable for anal sex. With this method of dosing, it is vital that you don’t miss any doses. You must also know if you are going to engage in unprotected sex a full 24 hours in advance. You must take 2 pills 2 to 24 hours prior to engaging in sex, 1 pill 24 hours after sex, and 1 more pill 24 hours after that. If you continue to engage in sex over an extended period, for instance over a few days or a weekend, continue taking 1 pill every 24 hours. Once you have 2 days where you have not engaged in sexual activity, then you can stop taking the medication.

Another dosing option is known as the Ts and Ss method. This is suitable for anal sex only, for individuals who have sex once or twice a month. It involves taking 4 pills weekly, one on Tuesday, Thursday, Saturday, and Sunday, after the initial daily dosing for 7 days.

PrEP can be taken with or without food.

PrEP Side Effects

Clinical trials have proven that pre-exposure prophylaxis is a safe and effective method of preventing HIV infection. However, there are some possible side effects associated with its use.

Common Side Effects

  • Nausea
  • Vomiting
  • Fatigue
  • Dizziness

Severe Side Effects

  • Kidney dysfunction


PrEP should be taken as prescribed by your health care professional, following one of the methods outlined in section 3. Truvada tablets for PrEP are available in 4 different dosage strengths:

  • 200 mg of emtricitabine and 300 mg of tenofovir disoproxil fumarate
  • 167 mg of emtricitabine and 250 mg of tenofovir disoproxil fumarate
  • 133 mg of emtricitabine and 200 mg of tenofovir disoproxil fumarate
  • 100 mg of emtricitabine and 150 mg of tenofovir disoproxil fumarate
Disclaimer: Please note that the contents of this article are for informational purposes only and should not be considered medical advice. This article, and other AIDS and HIV Information articles on AIDS Drugs Online, are not written by AIDS Drugs Online or reviewed by its staff for medical validity. All views and opinions expressed by the third-party authors are not endorsed by AIDS Drugs Online or its staff. Always consult a medical professional for medical advice.


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