Does cannabis use lead to heroin addiction?

Some pieces of evidence suggest the significant association of cannabis use with heroin use at earlier follow-ups of the ATOS*, but these data are scant and inconsistent across time points, reports a study.

In general, the evidence is not enough to demonstrate a uni- or bidirectional relationship between the use of these substances.

A total of 615 individuals with heroin dependence in 2001 and 2002 were recruited in ATOS. Participants were reinterviewed at 3, 12, 24, and 36 months as well as 11 and 18‒20 months after baseline.

The authors assessed the use of cannabis and heroin at each time point using the Opiate Treatment Index. They also conducted a random-intercept cross-lagged panel model analysis to identify within-person relationships between cannabis and heroin use at subsequent follow-ups.

An increase in the use of cannabis 24 months after baseline showed a significant correlation with an increase in heroin use at 36 months (estimate, 0.21) after accounting for a range of demographic variables, other substance use, and mental and physical health measures.

An increase in the use of heroin at 3 and 24 months also significantly correlated with a decrease in cannabis use at 12 months (estimate, ‒0.27) and 36 months (estimate, ‒0.22). Of note, other cross-lagged associations did not reach statistical significance.

“Cannabis use is common among individuals with opioid use disorder, but it remains unclear whether cannabis use is associated with an increase or a reduction in illicit opioid use,” the authors said.

*Australian Treatment Outcome Study