A study published by the American Journal of Psychiatry in 2017 found that "cannabis use appears to increase rather than decrease the risk of developing nonmedical prescription opioid use and opioid use disorder." In both the raw data and after controlling for several factors, cannabis users were 2 to 8 times more likely to abuse opioids. Because association does not prove causation, the study cannot definitively prove that cannabis leads to opioid abuse, but the authors outline these and other mechanisms that may cause this to occur: (1) Heroin and THC "have similar effects on dopamine transmission." (2) Cannabis "use can lead to behavioral disinhibition, which can increase the risk of using other substances, including opioids."