Disorders of cannabis use may be influenced by a number of genes that are difficult to detect because they may each have a small effect on the broad clinical phenotype. However, the genes influencing cannabis use disorders might be detected if they have a major effect on more narrowly defined phenotypes that more closely index the biological processes associated with addiction. Several biologically based theories have been suggested to explain the compulsion to use addictive drugs that might be profitably used to develop phenotypes useful for the study of cannabis use disorders. A general theory of addiction posits that the neurobiological mechanisms underlying the homeostatic regulation of appetitive drives and instincts becomes dysregulated during the process of drug exposure [Koob, 2000]. Some measures of the strength of this process include an increase or strong desire to take the drug often called ‘drug craving’ [see Anton, 1999], and ultimately the development of tolerance to and withdrawal from use of the drug [Schuckit, 1995]. Some studies have shown that requiring the presence of craving and withdrawal for the diagnosis of alcohol dependence
