A Noncausal Relation Between Casual Sex in Adolescence and Early Adult Depression and Suicidal Ideation: A Longitudinal Discordant Twin Study.

Research on relations between casual sex and mental health is inconclusive; while some studies indicate casual sex may lead to more negative mental health (e.g., depression), other studies report no such relationship. Using a genetically informed approach, this study examined whether earlier casual sex (i.e., ever engaging in casual sex and number of casual sex partners) in adolescence has a causal influence on later mental health in young adulthood (i.e., depressive symptoms and suicidal ideation), as well as the reverse relationship (adolescent negative mental health on young adult casual sex) by exploiting the quasi-experimental nature of discordant-twin models. Multilevel models that measured within-twin and between-twin pair effects of adolescent casual sex were estimated, using 714 twins (357 twin pairs) from the sibling subsample of the National Longitudinal Study of Adolescent Health (Add Health). Results indicated that there was no causal relationship between casual sex in adolescence and higher levels of depressive symptoms or suicidal ideation in young adulthood, and these effects did not differ by gender. There were also no causal relations between adolescent depressive symptoms or suicidal ideation and casual sexual experience in young adulthood. Implications for ways to increase scientific rigor by using different methods (e.g., genetically informed analyses) are discussed.