Effects of marriage equality legislation on sexual health of the US population

Even though prior research has investigated the relationship between same-sex partnership recognition policies and health outcomes, the impact of same-sex marriage laws on sexually transmitted infections has not received much attention. Using state-level panel data from 2000 to 2019, I show that marriage equality legislation decreases the spread of (shorter-term) syphilis infections and of (longer-term) human immunodeficiency virus (HIV) and acquired immunodeficiency syndrome (AIDS) infections among the general population. Event study analyses correcting for non-staggered treatment implementation confirm these negative effects, but also suggest that standard difference-in-differences models understate the impact of the legislation by up to 8% points. Further analysis supports that these legislation effects operate through three mechanisms: increasing social tolerance, strengthening relationship commitment, and expanding health care access and coverage for HIV/AIDS prevention and treatment. Disaggregating the results by sexual behavior reveals that legal access to same-sex marriage leads to sizable decreases in AIDS rates among men who have sex with men (MSM) (the most at-risk population for an infection). Even though there is economically significant evidence that the legislation improves sexual health of the heterosexual population due to increased utilization of preventive sexual health care, the legislation does not have a direct impact on infection rates for the non-MSM population.