Addictive drugs affect behavior through their effects on the brain "reward system" - the production of dopamine, linked to the pleasure sensation. This brain "reward system" has a powerful influence over behavior. Dependence-producing drugs - drugs that, unlike marijuana, affect dopamine production - eventually exert more influence on the user's behavior than any other factor. The effect of addiction on behavior is so profound as to create a condition called denial, in which someone will say or do anything to continue access to the drug.

Denial is a characteristic of drug abuse, and it is largely cultivated by the effects of various drugs on the brain reward system. Herkenham's research provides a clinical basis for claims that denial is not a characteristic of marijuana use.