Despite growing agreement that cannabis withdrawal contributes to the liability to cannabis use disorders, little is known of its etiology, particularly from a genetic perspective. With regard to cannabis abuse and dependence, several lines of research suggest a genetic influence. A meta-analysis of twin studies by Verweij et al. (2010) estimated a heritability (h2) of 51% in males and 59% in females for problematic cannabis use. Recently, Gillespie et al. (2011) found that a general latent factor representing cannabis use disorders, including withdrawal criteria, was also substantially heritable (h2=54% for males and 53% for females). However, only a few studies have specifically examined the heritability of cannabis withdrawal symptomatology. Agrawal et al. (2008) demonstrated a strong association between cannabis withdrawal symptoms and parental drug and alcohol problems, after controlling for the intensity of cannabis use in the past 12 months. This finding suggests that cannabis withdrawal symptoms are partly influenced by familial (possibly including genetic) factors not overlapping with heritability of use and heavy use of cannabis. Furthermore, using a family-based sample, Ehlers et al. (2010) found a heritability of
