It is worth noting the differences in the association between polygenic risk and heavy episodic drinking across the main effect and interactive effect models. In the main effects model, we found no association between polygenic risk and heavy episodic drinking. However, in the interaction model where we examined marriage as a moderator of the association between polygenic risk and heavy episodic drinking, a statically significant main effect of polygenic risk emerged. Importantly, main effects cannot be directly interpreted in the presence of an interaction effect (Aiken & West, 1991). Moreover, the null effect of the polygenic risk score in the main effects model, and its moderation by marital status in the interaction model, underscores that genetic influences on complex traits, such as heavy episodic drinking, can have a differential impact depending on the environment. Consistent with this possibility, in this study we observed a crossover effect for the polygenic risk score as a function of participants’ marital status and age. This suggests that the association between polygenic risk and heavy episodic drinking is dependent on marital status, such that genetic liability had a stronger impact on heavy episodic drinking among individuals who married relatively young.
