Bipolar disorder has the highest rate of substance abuse comorbidity of any axis I disorder (i.e. clinical psychiatric disorders, including major mental disorders according to the DSM-IV categorical classification system). Although cannabis use is common in bipolar patients, not much is known about its role as a risk factor for bipolar disorder. Clinical manifestations of chronic use of cannabis include abuse or dependence, tolerance to the subjective and cardiovascular effects, withdrawal, cardio-respiratory complications, and cognitive changes. Withdrawal symptoms include negative mood, irritability, anxiety, misery, muscle pain, chills, decreased food intake, craving and insomnia. Withdrawal likely contributes to the high rates of relapse observed clinically. In bipolar patients, chronic use of cannabis can exacerbate their presenting symptoms. The scarce research regarding effective treatment in this patient population is far from conclusive. Insomnia in chronic use of cannabis occurs presumably because of the effects of cannabis on the cannabinoid 1 (CB1) receptors. Open label trials have provided limited evidence that quetiapine may be effective in treating affective and substance use symptoms in bipolar patients with alcohol dependence suggesting a practical use of this atypical antipsychotic in bipolar patients with cannabis addiction. Quetiapine normalises sleep in this population, not just due to the antihistamine effects but also involving its action and antagonism on 5HT1A, 5HT2 and D2 receptors.