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Scientists study computer simulation of implementing over-the-counter HIV pre-exposure prophylaxis
CATIE News
SEPTEMBER 8, 2026
- Scientists in the U.S. modelled the potential effects of making PrEP available over the counter
- Increasing PrEP use by 50% would result in a 15% decrease in new HIV transmissions
- The model also estimated risks of over-the-counter access on kidney injury and drug resistance
In clinical trials and demonstration projects, HIV pre-exposure prophylaxis (PrEP) is highly effective at reducing the risk for HIV infection. The forms of PrEP approved in Canada and most other high-income countries are as follows:
Oral formulations
- tenofovir DF (TDF) + FTC – sold as Truvada and available in generic formulations
- TAF (tenofovir alafenamide) + FTC – sold as Descovy
Long-acting injectable formulations
- cabotegravir (Apretude)
- lenacapavir (Yeztugo) – this injectable formulation of the drug lenacapavir for the prevention of HIV was approved in Canada and other high-income countries in the past year; however, because it was only recently approved, it is not widely used.
The most widely used formulation of PrEP is TDF + FTC, chiefly because of its relatively low cost.
Significantly reducing new HIV infections will likely require increased access to HIV testing, PrEP and retention in PrEP care.
Engagement in PrEP care begins with contact with a healthcare provider. This can happen at a clinic or, in some cases, via telephone or video calls. Subsequent steps include a discussion of HIV risk, screening for HIV and other sexually transmitted infections (STIs), and offering treatment or referral for treatment if any tests come back positive. When the HIV test result is negative, a prescription of PrEP usually follows. Once PrEP is initiated, regular clinic visits and lab testing are needed to ensure that PrEP users remain HIV negative.
Some people who want PrEP may perceive these steps and requirements as barriers, particularly the initial visit. What’s more, some communities have encountered stigma from the healthcare system, which could be a potential barrier to access.
Although regular lab tests and healthcare visits may be inconvenient, they are essential for staying healthy while taking PrEP. One way to simplify access to PrEP for some populations could be by making it accessible over the counter (without a prescription).
Simulating the effect of more PrEP in the U.S.
A team of researchers from Emory University in Atlanta and other universities cooperated and developed a complex computer model, or simulation, of the HIV pandemic in Atlanta. They focused on gay, bisexual and other men who have sex with men (gbMSM) and used data from previous studies to estimate infection rates in different scenarios.
The team projected how increasing PrEP use could affect rates of new HIV infections over the coming decade. Researchers explored different scenarios, such as over-the-counter access to PrEP—in this case, daily use of a pill containing TDF + FTC.
Results
In the computer simulation, the researchers found that expanding access to PrEP by making it available over the counter reduced new cases of HIV infection. For instance, the simulation found that if PrEP use increased by 50%, this would result in a decrease of 15% in new HIV infections.
However, increasing access to PrEP by making it available over the counter also came with some negative consequences. The simulation estimated that nearly 5% of PrEP users could develop kidney injury.
Additionally, if PrEP is initiated by people who have HIV (but are unaware of their infection), the risk of HIV becoming resistant to the drugs in the most widely used PrEP pill (TDF + FTC) would increase by a factor of 12 over time. This is important because TDF, TAF and FTC are used as part of HIV treatment, but by themselves are insufficient to suppress HIV, hence the risk of resistance.
Issues with implementation of over-the-counter PrEP
The researchers stated that over-the-counter PrEP would likely “be most useful as a complementary, low-barrier entry point for individuals unwilling or unable to engage with clinic-based care, for whom prevention benefits outweigh low absolute risks.”
The researchers cautioned: “Rare adverse outcomes such as drug resistance may remain negligible at low [levels of PrEP] coverage yet become consequential when prevention tools are widely deployed without appropriate safeguards, so low-threshold pathways should be designed to expand coverage rather than merely redistribute existing clinic-based PrEP users across new delivery modalities.”
They noted that certain steps (what they referred to as “guardrails”) such as HIV testing prior to initiation of PrEP and subsequent monitoring of kidney health could, in theory, maintain the benefits of PrEP (seen with clinic-based care) when it is provided over the counter.
HIV testing prior to initiation of PrEP
To ensure that PrEP is not given to people with undiagnosed HIV, the research team suggested “pharmacist-facilitated testing” for this virus or bundling HIV self-tests with over-the-counter PrEP. However, they also noted that “because [HIV] antibody-based self-tests have a longer window period than laboratory testing and may miss acute infection, the state of highest resistance, real-world bundling [of HIV self-test kits] would achieve somewhat less reduction [of new HIV infections] than our model projects […].”
Reducing the chance of kidney injury
To minimize the possibility of kidney injury—a risk that can occur with the use of TDF-based formulations—the researchers stated that providing “accessible baseline and periodic assessment [of kidney function is necessary], particularly for older adults and those [who have pre-existing kidney injury or who are otherwise at risk for kidney injury].”
Minimizing the risk of hepatitis B virus (HBV) reactivation
Drugs such as TDF + FTC (or TAF + FTC) not only have potent activity against HIV but also against HBV. If a person has HBV and stops taking these medicines, there is a risk of HBV becoming reactivated and causing liver injury. Untreated HBV can lead to serious liver damage over time and increases the risk for liver failure and liver cancer. Therefore, the researchers stated that in cases where over-the-counter PrEP might be implemented, users should be made aware of their HBV status and, if necessary, be linked to care for HBV before initiating or stopping PrEP.
Limitations of the simulation
Computer simulations are imperfect and cannot always accurately model human behaviour. But they can be a useful guide for policy makers, particularly prior to conducting pilot studies to assess new interventions. The study’s authors advanced the following points about potential limitations of their simulation:
- The results depended on the use of daily oral PrEP, not long-acting formulations of PrEP.
- The researchers made clinic-based PrEP an ideal, assuming that it came with high levels of monitoring for adherence. It is possible that they may have “[overstated] the real-world performance of [clinic-based PrEP].”
- If access to clinic-based PrEP was to expand substantially over the next decade, the researchers stated that the benefit of over-the-counter PrEP “would depend increasingly on reaching individuals persistently excluded from existing care.”
- The computer simulation modelled over-the-counter PrEP as adding to, “rather than substituting for, clinic-based PrEP […].”
- The researchers did not include the impact of out-of-pocket costs that some people may incur in order to access over-the-counter PrEP.
Bear in mind
The computer simulation suggested that expanding access to PrEP (by making it available over the counter) could, in theory, result in reduced cases of new HIV infections over a decade. However, for this to occur, the researchers suggested that “HIV status confirmation at initiation should be accessible and actively promoted, and clinical risks, particularly [HIV resistance] at initiation and kidney [injury] in older users, should be addressed through targeted communication, differentiated eligibility guidance, and accessible period monitoring.”
The researchers added: “While OTC PrEP alone is unlikely to achieve national incidence-reduction targets, it could be an efficient component of a differentiated prevention toolkit, extending protection to underserved populations.”
Computer simulations cannot fully capture the richness and complexity of human life. Therefore, their findings should be viewed as a starting point for discussions among stakeholders, and perhaps a prelude to pilot studies.
—Sean R. Hosein
Resources
Prescribing PrEP and PEP: Canadian Guideline – CATIE and CIHR Pan-Canadian Network for HIV and STBBI Clinical Trials Research (CTN+)
PrEP pharmacist and navigation services at a sexually transmitted infection clinic – CATIE
Lenacapavir (Yeytuo) injected every six months approved for HIV prevention in Canada – CATIE News
Canadian study finds that many more people could be using HIV pre-exposure prophylaxis to reduce HIV risk – CATIE News
Protection is prevention: The importance of hepatitis B vaccination – Prevention in Focus
REFERENCES:
- Le Guillou AV, Marcus JL, Krakower DS, et al. Potential risks and benefits of low-barrier access and monitoring for HIV preexposure prophylaxis: A modeling study. Journal of Infectious Diseases. 2026; in press.
- Krakower D, Marcus JL. Free the PrEP – Over-the-counter access to HIV preexposure prophylaxis. New England Journal of Medicine. 2023 Aug 10;389(6):481-483.
- Arapali T, Warzywoda S, Fontaine G, et al. Barriers and facilitators to oral HIV pre-exposure prophylaxis use in Australia: A scoping review comparing findings to Canada, New Zealand, and the United Kingdom. AIDS and Behavior. 2026; in press.
- Oo MM, Karabelas-Pittman S, Hull M, et al. Impact of “absolute” versus “relative” HIV risk communication on pre-exposure prophylaxis interest in Canada: a randomized survey. AIDS Care. 2025 Nov 19:1-12.
- Orser L, MacPherson P, O’Byrne P, et al. Use of HIV pre-exposure prophylaxis among men who have sex with men: low uptake and retention despite high-risk indications. AIDS Care. 2025 Jan;37(1):141-150.
- Turpin R, Camp AD, Mandell CJ, et al. “Healthcare Doesn’t Care”: A mixed-methods study on healthcare stigma and PrEP use among Black sexual minority men. American Journal of Health Promotion. 2025 Sep;39(7):991-999.
- Psaros C, Hill-Rorie J, Quint M, et al. A qualitative exploration of how to support PrEP adherence among young men who have sex with men. AIDS Care. 2024 Jun;36(6):732-743.
From Canadian AIDS Treatment Information Exchange (CATIE).
This content was originally published by CATIE, Canada’s source for HIV and hepatitis C information.
Source: CATIE:
https://www.catie.ca/catie-news/scientists-study-computer-simulation-of-implementing-over-the-counter-hiv-pre-exposure
For more information visit CATIE's Information Network at www.catie.ca
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