are significantly heritable including: having ever used cannabis, used more than 21 times in a single year, DSM-IV cannabis dependence, individual criteria of DSM-IV cannabis dependence [Ehlers et al., unpublished work]. Two phenotypes with the highest heritability were cannabis “craving” and withdrawal. Therefore, the phenotypes chosen for the present linkage analyses were: (1) a DSM-IV cannabis dependence diagnosis; (2) cannabis “craving” defined as endorsing: “In situations where you couldn't use marijuana, did you ever have such a strong desire for it that you couldn't think of anything else”; and (3) a measure of cannabis withdrawal defined as: “Did stopping or cutting down after a period of regular use of marijuana ever cause you to feel nervous, tense, restless or irritable”. The number of participants with each phenotype, with and without co-morbid alcohol dependence, is presented in table 1. Twenty percent of those enrolled did not complete all study requirements. Details of the interview process and inter-rater reliability of the SSAGA in this study have been reported previously [Vieten et al., 2004].
