With the exception of opiates (including heroin and prescription versions), individuals who commit suicide by intentionally overdosing show very similar patterns of drug use as people who commit suicide by other means, according to a study by the Centers for Disease Control (CDC).
Unfortunately, none of the thirteen states used in this study test all suicide victims for substances, and none tested for antidepressants or other psychotropic drugs. The data do not indicate whether or not a person used a drug habitually, or used a drug in order to overcome barriers to making a suicide attempt.
The CDC is hoping to engage in further research to clarify the roles of substance abuse and suicide. Improvements in our understanding of this relationship will hopefully lead to better prevention.