BACKGROUND: Reasons for first using cannabis (RFUC) may influence later use patterns and mental health outcomes. However, limited research has explored self-medication versus social RFUCs in depth, and their associations with cannabis use patterns and psychopathology in the general population.

OBJECTIVES: We examined RFUCs and their associations with (1) reasons for continuing cannabis use, (2) weekly THC (delta-9-tetrahydrocannabinol) unit consumption and (3) symptoms of paranoia, anxiety and depressive symptoms.

METHODS

We analysed data from the Cannabis&Me (CAMe) population survey (March 2022-July 2024), including 2573 (75.9%) current and 816 (24.1%) past cannabis users aged 18 years or older.

FINDINGS: Participants reported a mean weekly consumption of 206 THC units (SD=268). Initiating cannabis use for anxiety (β=36.22, p=3.3e-03), depression (β=40.37, p=1.74e-03) or because 'family members were using it' (β=87.43, p=1.22e-09) was associated with higher weekly THC units. RFUC to relieve physical discomfort (β=8.89, p=4.12e-07), pain (β=7.24, p=5.56e-06), anxiety (β=9.67, p=1.63e-16), depression (β=9.12, p=1.21e-13) and minor psychotic symptoms (β=16.46, p=1.2e-04) were linked to higher paranoia scores. Similar associations were observed for anxiety and depression. Conversely, starting for fun (β=-3.71, p=3.49e-05) or curiosity (β=-2.61, p=5e-03) was associated with lower paranoia and anxiety. RFUC for 'boredom' was linked to increased depression (β=1.09, p=3.8e-03).

CONCLUSIONS: Initiating cannabis use for self-medication is associated with higher average THC consumption, and increased anxiety, depression and paranoia.

CLINICAL IMPLICATIONS: Asking individuals why they first used cannabis may serve as a cost-effective screening tool to identify those who could benefit from monitoring, support, or referral to intervention services.