A previous post reviewed data about drug use among sexual and gender minority people. In addition to its direct health risks, drug use is associated with an increased risk of HIV infection. It might be surprising to know that intravenous drug use—and the transmission of HIV through sharing infected works—is only one part of the explanation for this.
The United States had an estimated 31,800 new HIV infections in 2022 according to the Centers for Disease Control and Prevention (CDC). About 7 percent were attributed to intravenous drug use. The rest (minus a small number for which a likely source could not be determined) were attributed to sexual transmission—penetrative sex without a condom or the use of pre-exposure prophylaxis (PrEP). The risk is greater for anal, versus vaginal, intercourse. Partly for this reason, sexual minority men account for approximately 67 percent of those recent HIV infections; meanwhile, heterosexual sexual contact accounts for 22 percent.
The CDC no longer provides surveillance data for gender minority people. Previous studies have estimated the odds of HIV acquisition among transgender women were as much as 48.8 times greater than the general population (Baral et al., 2013) with estimated HIV prevalence ranging from 14.1 to 21 percent (Becasen et al., 2019; CDC, 2021, 2022).
So the overwhelming majority of new HIV infections are sexually transmitted. What is one of the most reliable predictors of having sex that is likely to transmit HIV infection?
The answer is drug use.
Drug use and sexual HIV transmission risk
The use of illicit drugs has been consistently linked to condomless sex (Lloyd et al., 2020; Petersson et al., 2016). In particular, the use of a number of illicit drugs (most commonly cocaine or crack, amphetamines including methamphetamine, ecstasy, ketamine, and gamma-hydroxybutyrate [GHB]) has been associated with either the occurrence or frequency of condomless anal sex with casual partners across a range of studies involving sexual minority male adults (Starks et al., 2020) and adolescents (Cain et al., 2023; Cain et al., 2021). Similar results have been observed in studies of transgender women (Cain et al., 2025) and their relationship partners (Skeen et al., 2021) as well as nonbinary people assigned male at birth (Cain et al., 2025).
These kinds of cross-sectional survey studies provide evidence that people who use drugs are also more likely to have the kinds of sex that might transmit HIV or other sexually transmitted infections. They do not directly show that people are having sex at the same time they are using drugs. To do that, studies have to gather data about the specific days on which these behaviors occur. Results from these kinds of studies demonstrate that sexual minority men in fact are more likely to have condomless sex with casual partners on the days that they also use illicit drugs (e.g., Halkitis et al., 2016; Rendina et al., 2015; Starks et al., 2021).
Relationships, sexual agreements, and the drug–sex association
Research on the association between drug use and sexual behavior among people in relationships has largely focused on sexual minority men. Overall (without making distinctions about sexual agreements), sexual minority men in relationships combine sex and drug use at rates comparable to those who are single. In one survey, 33 percent of respondents said they used cannabis and 12.5 percent reported illicit drug use during sex with their main partner. Similarly, 31 percent of these respondents said they used cannabis and 10.6 percent said they used illicit drugs during sex with casual partners (for illicit drugs; Mitchell, 2016). For comparison, data from the CDC from around the same period suggest that 31 percent of sexual minority men overall reported using cannabis or illicit drugs during sex (CDC, 2016).
Previous posts introduced the idea that illicit drug use and sexual behavior are associated with sexual agreements. Studies of sexual minority men and transgender women indicate those in monogamous relationships are less likely to use illicit drugs and have condomless sex with casual partners compared to those in nonmonogamous relationships (e.g., Cain et al., 2025; Starks et al., 2020).
There is now mounting evidence that sexual agreements also contextualize the association between drug use and sex. In one of the largest cross-sectional studies to examine this question, Starks, Jones, Kyre, and colleagues (2020) found that, among single sexual minority men and those in relationships with nonmonogamous agreements, those who used illicit drugs were at least three times more likely to have condomless sex with a casual partner compared to those who did not.
For sexual minority men in relationships with monogamous agreements, having sex with a casual partner presumably means they are breaking their agreement. Those who used illicit drugs were a little less than twice as likely to have condomless sex with a casual partner. That association is still large (and statistically significant); however, it is also significantly smaller in magnitude compared to the illicit drug–sex association among single sexual minority men and those in relationships with nonmonogamous agreements.
Conclusions
Caution is warranted when thinking about causality. It is possible that drug use leads people to seek out sex and interferes with the use of condoms or PrEP adherence in ways that make sex riskier. It is also possible that sex provides a motivation for drug use. For some, drug use serves to decrease sexual inhibitions, enhance pleasure, or create a sense of emotional connection to sexual partners (Bourne, Reid, Hickson, Torres-Rueda, & Weatherburn, 2015; Milhet et al., 2019; Starks et al., 2015). In some contexts—often referred to as party-and-play or ChemSex in the United States and United Kingdom—combining sex (often without condoms) and drug use is normative (Bourne, Reid, Hickson, Torres-Rueda, Steinberg, et al., 2015; Bourne, Reid, Hickson, Torres-Rueda, & Weatherburn, 2015; Souleymanov et al., 2021).
Although multiple causal explanations are possible, one thing is clear. The association between drug use and HIV transmission risk is not limited to intravenous drug use. A major component of the health impact drug use has on sexual and gender minority people comes through its associations with sex, sexual health, and sexual risk-taking.