Early reactions to cannabis predict later dependence

CONTEXT: While there is a growing literature on the linkages between early subjective responses to nicotine and alcohol and later risks of nicotine or alcohol dependence, to date there has been no study of this issue in relation to cannabis.
OBJECTIVE: To examine the extent to which subjective responses to early (prior to the age of 16 years) cannabis use were associated with subsequent cannabis dependence in a birth cohort studied to the age of 21 years. DESIGN: Data on early (prior to the age of 16 years) subjective reactions to cannabis use and subsequent cannabis dependence were gathered over the course of the Christchurch Health and Development Study, a 21-year longitudinal study of a birth cohort of children born in Christchurch, New Zealand.
SETTING: General community sample.
PARTICIPANTS: Members of a population-based birth cohort (86.5% white, 11.3% New Zealand Maori, and 2.2% Pacific Island).Main Outcome Measure Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition cannabis dependence (for those aged 16-21 years).
RESULTS: Of the cohort, 198 (20%) had used cannabis prior to the age of 16 years. Among this high-risk group, rates of dependence were high with 21.7% meeting DSM-IV criteria for cannabis dependence by the age of 21 years. There were clear tendencies for rates of cannabis dependence to increase with increasing reports of positive responses to early cannabis use: those reporting 5 positive responses had odds of cannabis dependence that were 28.5 (95% confidence interval, 6.3-133.8) times higher than those not reporting positive reactions to cannabis. The association held (odds ratio, 23.4; 95% confidence interval, 4.0-135.9) after control for potentially confounding factors including the extent of use of cannabis prior to age 16 years. The extent of early negative reactions to cannabis was unrelated to later cannabis dependence.
CONCLUSIONS: Early subjective responses to cannabis are prognostic of later cannabis dependence. These findings may suggest the presence of genetically mediated individual differences in early responsiveness to cannabis. Clinicians should be aware that young people who report positive reactions to early use of cannabis are at increased risks of later cannabis dependence.