Factors associated with the onset of cannabis use: a systematic review of cohort studies.

OBJECTIVE

To determine the factors associated with the onset of cannabis use through a systematic review of cohort studies.

METHODS

An internet-based search was performed using several keywords and their combinations. Original studies with longitudinal design and the onset of cannabis use as dependent variable, as well as review studies were included, published between January 1980 and May 2004. Methodology quality of the studies was assessed independently by two reviewers, according to pre-established criteria, in order to classify studies in high, mid or low quality. Agreement between reviewers was assessed through kappa coefficient.

RESULTS

A total of 32 relevant studies were identified, of which 13 were of higher quality. Selection bias for the inclusion of consumers at the baseline measurement and lack or insufficient adjustment for confounders were the causes of exclusion. The factors of great evidence related to the onset of cannabis use were masculine sex, consumption of tobacco or alcohol, having a problematic relationship with parents, and cannabis consumption by friends.

CONCLUSION

Results highlight the importance of different individual, family and environmental factors on the onset of cannabis use. These must be considered to properly arrange intervention programs focusing on primary prevention among teenagers.