In 1994, when DSM-IV was published, symptoms of cannabis withdrawal had been described in earlier studies and case reports. 9–11 However, the evidence for the validity of a cannabis withdrawal syndrome was considered too weak to include cannabis withdrawal in DSM-IV. Since then, evidence has accumulated from animal,12 inpatient laboratory,13–15 prospective non-laboratory, 16–18 clinical, 19,20 and other retrospective studies 21,22 indicating the occurrence of cannabis withdrawal symptoms, typically beginning within a few hours or days after cessation of cannabis use. Importantly, placebo-controlled laboratory studies show that administration of delta-9 THC suppresses cannabis withdrawal symptoms,23,24 indicating the pharmacological specificity of the cannabis withdrawal syndrome. Cannabis withdrawal symptoms commonly identified in these studies include anxiety, irritability, various types of physical discomfort, negative affect, and appetite and sleep changes.25 A recent study based on a convenience sample of non-treatment seeking cannabis users suggested that cannabis withdrawal symptoms clustered into two components, a physical and a psychological component.22
