PrEP doesn't lead to increases in risky sex among gay men

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Taking HIV pre-exposure prophylaxis (PrEP) does not lead to increased levels of sexual risk behaviour among gay men, investigators from the United States report in the online edition of the Journal of Acquired Immune Deficiency Syndromes. Numbers of sexual partners fell, as did the proportion of men reporting unprotected anal sex.

“We found no evidence of risk compensation among at-risk MSM [men who have sex with men] initiating PrEP,” comment the authors. “Mean numbers of partners and the proportion of men reporting UAS [unprotected anal sex] decreased significantly from baseline during 24 months of follow-up.”

PrEP is an emerging HIV prevention technology. It involves HIV-negative individuals taking daily antiretroviral therapy to reduce their risk of infection with the virus. In 2010, results of the iPrEx trial involving gay and other MSM showed that daily PrEP with Truvada (FTC and tenofovir) reduced the risk of infection with HIV by 44% overall, with high efficacy seen in people with the best treatment adherence. Although the results of PrEP studies involving heterosexuals have been mixed, the United States Food and Drug Administration approved Truvada for use as PrEP by adults with a high risk of HIV infection.


risky behaviour

In HIV, refers to any behaviour or action that increases an individual’s probability of acquiring or transmitting HIV, such as having unprotected sex, having multiple partners or sharing drug injection equipment.


Amyl, butyl or isobutyl nitrite, are recreational drugs sniffed during sex to both intensify the experience and relax anal sphincter muscles.

Food and Drug Administration (FDA)

Regulatory agency that evaluates and approves medicines and medical devices for safety and efficacy in the United States. The FDA regulates over-the-counter and prescription drugs, including generic drugs. The European Medicines Agency performs a similar role in the European Union.

linkage to care

Refers to an individual’s entry into specialist HIV care after being diagnosed with HIV. 

mathematical models

A range of complex mathematical techniques which aim to simulate a sequence of likely future events, in order to estimate the impact of a health intervention or the spread of an infection.

However, there is concern in some quarters that use of PrEP may lead to increases in sexual risk behaviour. Mathematical models suggest that even modest increases in the proportion of gay men reporting unprotected sex could wipe out the beneficial effect of PrEP at a community level. However, the precise impact of PrEP on sexual risk taking is highly controversial.

Data gathered during a PrEP safety study allowed investigators to explore the impact of PrEP on the sexual risk behaviour of HIV-negative gay men with a high risk of infection with HIV.

A total of 400 men were recruited to the study between 2005 and 2007. All reported anal sex with another man in the preceding twelve months. The study was double blind and placebo controlled. Participants were randomised either to start treatment immediately or to wait for nine months. The men were interviewed at baseline and then every three months about their sexual risk behaviour and use of recreational and erectile dysfunction drugs. The study lasted 24 months.

At baseline, the men reported a mean of 7.25 sexual partners in the previous three months. This fell significantly during follow-up to a mean of 6 partners between months 3 and 9 and a mean of 5.71 partners between months 12 and 24 (p < 0.001). These declines were similar in the immediate- and delayed-treatment arms.

The mean number of reported HIV-positive partners or partners of an unknown status fell from 4.17 at baseline to 3.51 partners between months 3 and 9 and 3.37 partners between months 12 and 24 (p = 0.01). There was also a significant fall in the number of reported partners believed to be HIV negative.

Use of poppers (p < 0.001), erectile dysfunction drugs  (p < 0.001) and a higher perception of the efficacy of PrEP (p = 0.04) were all associated with reporting higher numbers of sexual partners during follow-up.

At the start of the study, 57% of men reported unprotected anal sex in the previous three months. The proportion fell to 48% between months 3 and 9  (p = 0.001) and to 52% between months 12 and 24 (p = 0.03).

The proportion of men reporting unprotected sex between months 3 and 9 was similar between the immediate- and delayed-treatment arms.

There was also a fall in the proportion of men reporting unprotected sex with an HIV-positive partner, from 29% at baseline to 21% between months 3 and 9 and 22% between months 12 and 24 (p < 0.001). Declines in unprotected sex with HIV-positive partners were seen in both the immediate- and delayed-treatment arms.

Factors associated with reporting unprotected sex during follow-up included younger age (p = 0.01), use of poppers (p = 0.02), erectile dysfunction treatments (p < 0.001) and methamphetamine (p < 0.001).

Participation in the study did not lead to an increase in the number of reported episodes of unprotected anal sex, which remained steady between months 3 and 9 and months 12 and 24 in both the immediate- and delayed-treatment arms.

There was a fall in reported episodes of unprotected sex with HIV-positive partners from two in the previous three-month period at baseline to 1.37 between months 12 and 24 (p = 0.05). This was the case for both the immediate- and delayed-treatment study arms.

In contrast, the number of episodes of unprotected anal sex with partners thought to be HIV negative increased between baseline and months 12 and 24 (2.75 Vs. 4; p = 0.01).

“These changes may represent a possible increase in seroadaptive practices, in which men preferentially have more episodes of UAS with assumed HIV-negative partners,” comment the authors.

They also note “men in this study received risk-reduction counseling, condoms and lubricants, regular HIV/STI testing, and linkage to prevention services…which may explain the observed risk reduction and could explain the observed risk declines and could mitigate any potential for risk compensation.”

Despite this, the investigators were encouraged by their results, which they believe “provide important information on changes in risk practices among MSM in the US initiating PrEP in a clinical trial setting”.


Liu AY et al. Sexual risk behavior among HIV-uninfected men who have sex with men (MSM) participating in a tenofovir pre-exposure prophylaxis randomized trial in the United States. J Acquir Immune Defic Syndr, online edition, DOI: 10.1097/QAI.0b013e31828fo97a, 2013.