Aims
This study investigates associations of patterns of cannabis use from adolescence to middle age with mental health outcomes in middle age. The availability of cannabis use data and outcomes this late in life is rare.
Design and setting
Prospective observational study using data from the British Cohort Study (BCS) and the National Child Development Study (NCDS).
Participants
NCDS: 9,137 respondents born in the UK in 1958. BCS: 9,839 respondents born in 1970.
Measurements
Self-reported lifetime and past 12 month cannabis use was reported at age 16, 30 and 34 in the BCS, and at age 42 in NCDS. We adjusted for pre-cannabis use mental health, sociodemographics, personality and other substance use. Mental health was assessed at age 50 in NCDS, and at age 46 in BCS Outcomes include: psychological distress (9-item Malaise Scale); psychological wellbeing (Warwick-Edinburgh Mental Wellbeing Scale); and cognitive function including memory (delayed and immediate word-recall task) and executive function (letter-cancellation task and animal naming task).
Findings and conclusions
After adjustment for covariates, cannabis use was not significantly associated with cognitive functioning. In BCS, adult use (but not adolescent use) was associated with malaise and low wellbeing. In NCDS, recent (but not lifetime) use was likewise associated with malaise and low wellbeing. The results contradict previous findings about the role of adolescent cannabis use, particularly for cognitive functioning and IQ, but suggest that use in mid-adulthood is predictive of mental health. The results highlight the importance of confounding in previously identified associations.