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Cannabis potency (percentage of tetrahydrocannabinol [THC%]) has increased almost fourfold in the last 2 decades. Preliminary, mostly cross-sectional studies indicate that potency increases the risk for harm (e.g., psychosis, accidents, and cannabis use disorder [CUD]). These researchers used longitudinal data from annual and in-depth 3-year assessments in 527 cannabis users aged 11 to 26 (72% male, 89% white) who initiated use between 1994 and 2012.
Potency was defined by THC% in federally seized supplies across the U.S. Regular and daily use were associated with fewer years to first CUD symptom in analyses controlling for sex and birth year. In regressions additionally controlling for daily use and regular use, higher average national THC%…