Monthly patterns of depressive symptoms and substance use and their relation to longer-term hazardous substance use and mental health problems: Examining mutual maintenance using monthly data from young adults.

The current study examined whether young adults showing a pattern of greater substance use on months when experiencing greater levels of depressive symptoms showed long-term hazardous alcohol and cannabis use and elevated depressive symptoms. Data were from 772 young adults in Washington State (mean age = 21.1 years, SD = 1.7; 57 % female). For 24 consecutive months, surveys asked about past-month depressive symptoms and typical number of alcoholic drinks per week and typical number hours high on cannabis per week. Participants completed a survey 30 months after baseline that included measures of depressive symptoms and hazardous alcohol and cannabis use. Multilevel models showed substantial variability in monthly within-person associations of depressive symptoms with alcohol and cannabis use across individuals during the first 24 months. On months when experiencing increased depressive symptoms compared to their average, some young adults used more alcohol or cannabis and some used less. When linking outcomes at 30-month follow-up to person-specific slopes extracted from the multilevel models, results showed that young adults who tended to drink more or use more cannabis when they experienced more depressive symptoms than their average reported greater levels of hazardous alcohol and cannabis use at 30-month follow-up, respectively. Person-specific slopes were not associated with 30-month depressive symptoms. Although there was substantial variability in within-person monthly associations, findings suggest that young adults showing short-term patterns consistent with increased alcohol and cannabis use to regulate depressive symptoms may benefit from prevention and intervention efforts aimed at decreasing risk of longer-term problematic substance use.