What is PrEP?

PrEP (pre-exposure prophylaxis) is a class of medications that reduce the risk of HIV infection. It is available in tablet and injection formulations that patients can take once daily or monthly/every other month respectively. HIV (human immunodeficiency virus) is a virus that attacks the body’s immune system. There is currently no cure but treatment options are effective ways to prevent it. PrEP is used by people without HIV who may be exposed to HIV through sex or injection drug use. PrEP when taken correctly, reduces the risk of getting HIV from sex by 99% and reduces the risk of getting HIV from injection drug use by at least 74%.

Who should take PrEP, and how can you access it?

Individuals who are HIV negative, but have a high risk of being exposed to the infection should consider taking PrEP. This includes those who have an HIV positive partner and men who identify as gay or bisexual who have had anal sex without a condom, or have been diagnosed with an STD in the past six months. It is also beneficial for heterosexual men and women who regularly have sex without the use of a condom, or have sexual partners with unknown HIV status. Others who should consider using PrEP include those who use injectable drugs.

To get a prescription for PrEP, talk to a doctor to see if you are eligible for receiving PrEP. It generally requires individuals to have bloodwork and a physical examination done before starting treatment. After starting, patients must get HIV tested and see their doctor every 2-3 months. Most insurances cover PrEP, however prescription assistance programs are available for patients without insurance coverage who meet certain criteria. More information on assistance programs can be obtained from your doctor.

Treatment Options:

There are currently three PrEP medications that are approved for use in the United States:

Brand Name Active


Directions Side Effects Key Points
Truvada® emtricitabine and tenofovir disoproxil fumarate tablet Take one tablet by mouth once daily with or without food weight loss, headache, abdominal pain -if using for   prevention, patients must be tested HIV negative immediately before starting PrEP.


Descovy® emtricitabine and tenofovir alafenamide tablet Take one tablet by mouth once daily with or without food diarrhea -not recommended for patients weighing less than 35kg

-only effective for patients assigned male at birth and those who are HIV negative

Apretude® cabotegravir injection Two initiation doses of 3 mL (600mg) (one single dose vial) intramuscular injection given one month apart by health care provider, followed by one 600mg injection given every two months by healthcare provider injection site reactions, headache, fatigue -oral cabotegravir tablets are available and can be used for 28 days as a pre-treatment before starting Apretude injections to make sure you tolerate the medication

-does not require patient to remember to take doses daily

All of the agents above are contraindicated in patients who are tested positive for HIV or have undiagnosed HIV. All individuals MUST be tested before starting PrEP therapy. Sudden stopping oral PrEP agents also puts patients at risk for Hepatitis B infection. Individuals who plan on stopping PrEP treatment must first consult their doctor.

While consistent use of PrEP is considered the standard, “on-demand” PrEP use or non-daily use is also an effective treatment regimen for gay and bisexual men. This features the “2-1-1” use of PrEP pills— 2 pills taken 2-24 hours before sex, 1 pill taken 24 hours after the first dose, and 1 pill taken 24 hours after the second dose.

Frequently Asked Questions

  • Is PrEP safe?

PrEP is safe and has been prescribed globally for years. Health issues that may occur in some people while using PrEP are easily screened.

  • How long does it take for PrEP to work?

For those who have receptive anal sex (bottoming), PrEP pills take about 7 days of daily use to be effective. For those having receptive vaginal sex or for injection drug use, it takes about 21 days of daily use for the pills to be effective. Time taken for PrEP injections to start working is currently not known.

  • Does PrEP interact with other medications?

PrEP medications only have a few interactions with other medications. Consult your provider, a pharmacist, or the HIV Drug Interactions website for more information on possible interactions between your PrEP medicine and any prescription and non-prescription medicines and nutritional supplements you take.

  • Can a younger person take PrEP?

Individuals under 18 can take PrEP. Younger patients will also need additional support around adherence to help them remember taking doses while juggling school activities and to cope with stigma. For individuals who do not want others knowing about their PrEP use, Apretude®  injection may be a good option.

  • Does PrEP ever fail at providing HIV prevention?

PrEP is very effective in protecting against HIV but not a 100%. The most common case where PrEP can fail is if it is not taken consistently or as directed by a healthcare provider. Other rare cases include having sex with an HIV positive partner who is not being treated, or the rare development of HIV resistant strains.

Written by:

Janice Jaison
PharmD Candidate Class of 2025
Philadelphia College of Pharmacy
St. Joseph’s University


Apretude® Prescribing Information – gskpro. https://gskpro.com/content/dam/global/hcpportal/en_US/Prescribing_Information/Benlysta/pdf/BENLYSTA-PI-MG-IFU.PDF. Accessed November 4, 2022.

Descovy® Prescribing Information – Gilead Sciences.       https://www.gilead.com/-/media/55b14ac03ef94b6f98d5d3c31ea0137b.ashx. Accessed November 4, 2022.

On-demand prep. Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/basics/prep/on-demand-prep.html#:~:text=Taking%20PrEP%20pills%20only%20when,%2D1%2D1%E2%80%9D%20schedule. Published June 1, 2022. Accessed November 4, 2022.

Prep effectiveness. Centers for Disease Control and Prevention. https://www.cdc.gov/hiv/basics/prep/prep-effectiveness.html#:~:text=How%20long%20does%20PrEP%20take,21%20days%20of%20daily%20use. Published June 6, 2022. Accessed November 4, 2022.

Truvada® Prescribing Information – Gilead Sciences. https://www.gilead.com/~/media/Files/pdfs/medicines/hiv/truvada/truvada_pi.pdf. Accessed November 4, 2022.

UCSF Health. Pre-exposure prophylaxis (prep) to prevent HIV transmission. ucsfhealth.org. https://www.ucsfhealth.org/education/pre-exposure-prophylaxis-prep-to-prevent-hiv-transmission#:~:text=those%20other%20diseases.-,Who%20should%20take%20PrEP%3F,in%20the%20past%20six%20months. Published June 24, 2022. Accessed November 4, 2022.