Methods: Participants were recruited from an inpatient psychiatric unit in a large academic hospital in the northeast and included 71 adolescents (75% female; Mage=15.8) hospitalized for a suicidal event who also endorsed alcohol use in the past 90 days. Past 90-day NSSI, suicide plan, alcohol use, and cannabis use, were measured using the Timeline Follow Back Calendar (TLFB). Control variables, such as gender, age and race were assessed in the model.
Results: Fifty-six percent of participants endorsed NSSI on at least one day over the 90 day period. With respect to substance use, 77% used cannabis and 97% used alcohol on at least one day of the study period. There were 6,387 time-person observations nested within 71 participants. Results from the trajectory analyses indicated that the average odds of NSSI (OR=1.007, p=0.06), alcohol use (OR=1.005, p=0.09), and cannabis use (OR=1.00, p=0.72) remained stable across the 90 days. Results from a random effect model demonstrated that the independent use of alcohol and cannabis was not significantly predictive of NSSI (ps>0.05). However, their combined use increased the odds (OR=30.5, p<0.05) of NSSI on a given day.
Conclusions: Our study found that adolescents who used both cannabis and alcohol were at a significantly increased risk for NSSI on that same day in the period leading up to psychiatric hospitalization. Clinicians and health care providers should be aware that adolescents who use both alcohol and cannabis may be at increased risk for NSSI, and therefore, should be screening for these behaviors. This study is unique in that it utilized daily level data in order to assess the relationship among distinct suicide-related variables on a fine-grained level, and clarifies the relationships among cannabis use, alcohol use, and NSSI among adolescents leading up to psychiatric hospitalization.