Chemsex Doesn't Impact PrEP Adherence, New Study Finds

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Two years ago, researchers in London published a worrying study that found HIV-positive men who have sex with men (MSM) engaging in chemsex are less likely to adhere to their antiretroviral (ART) treatment.

However, new research presented at the 2019 National HIV Prevention Conference in Atlanta finds that chemsex doesn't seem to have a negative impact on overall pre-exposure prophylaxis (PrEP) adherence in at-risk MSM.

"Although there is evidence that chemsex has a negative impact on ART adherence, it doesn't seem to have the same association with PrEP adherence," said study coauthor Charlotte O'Halloran, senior scientist in HIV/STI surveillance and prevention with Public Health England.

Though loosely defined, chemsex is the practice of injecting or using party drugs (usually mephedrone, crystal methamphetamine, and/or gamma-hydroxybutyrate [GHB]) to enhance sexual pleasure and reduce inhibitions. There's evidence that it's on the rise among MSM across the globe, with sexual encounters facilitated by the ubiquity of social apps.

Chemsex has become an increasingly active area of research in the United Kingdom after multiple studies hinted at the association between chemsex and poor ART adherence.

The U.K.-based PROUD study was an open-label, randomized trial that was designed to look at the effectiveness of emtricitabine/tenofovir disoproxil fumarate (Truvada) as PrEP among 544 at-risk MSM. The study's primary goal was to evaluate PrEP as a risk-reduction tool, and it concluded that PrEP was associated with an 86% reduction in HIV risk.

The study also reported that 44% of HIV-negative MSM had engaged in chemsex at baseline, hinting at a widespread phenomenon that could be exacerbating HIV risk.

O'Halloran and other researchers were interested in using the extensive survey data from PROUD study participants to evaluate the relationship between chemsex and PrEP adherence. In these surveys, men were asked to rank their own ability to adhere to PrEP at baseline. In the follow-up period, they were asked about their chemsex behavior quarterly and self-reported whether they had missed any PrEP tablets monthly.

O'Halloran acknowledged that the self-report aspect of PrEP adherence is a major limitation of the follow-up study but also noted that participants were asked to rank their ability to answer honestly about missed PrEP doses -- a sort-of "back-up" self-assessment that helped strengthen the legitimacy of the self-reported responses. The researchers also used a relatively high standard for PrEP non-adherence that included any missed doses.

Ultimately, researchers collected 1,479 quarterly visit forms, which included information about chemsex behavior, and 2,260 monthly PrEP adherence forms. Of the 544 MSM enrolled in the original PROUD study, 388 were included in the subsequent analysis.

Because researchers were looking at the correlation of PrEP adherence and chemsex, they looked not at the individual study participants but rather at each individual visit form. About 39% of the visit forms reported chemsex in the past 90 days, and about 30% of those 90-day periods saw imperfect PrEP adherence.

The researchers then used a univariable analysis to draw connections between suboptimal PrEP adherence and other correlated demographics, and a few factors jumped out. Chiefly, suboptimal PrEP use was linked to those aged 18 to 25 and to those who predicted at baseline that they would have a hard time with PrEP adherence.

Importantly, there was no association between suboptimal PrEP use and chemsex -- a finding that persisted after the researchers controlled for age and prediction of PrEP use at baseline. (The adjusted odds ratio was 1.24 [95% confidence interval 0.88-1.75] and the P value was .22, falling well shy of the threshold for a statistically significant association).

According to O'Halloran, this study should serve as a welcome relief to care providers with questions about PrEP adherence among patients who engage in chemsex. In the U.K., where PrEP access is still limited, O'Halloran hopes this study will add to the growing evidence supporting the use of PrEP for all people at high risk for HIV.