Our results also indicated support for the validity of the cannabis withdrawal syndrome in the general population, as clinical distress/impairment and using to relieve or avoid symptoms were strongly related to both depression/anxiety and weakness in both samples. We did not find that age of onset of cannabis use predicted cannabis weakness or depression/anxiety withdrawal symptoms in either sample. This could be due to restricted variance of this variable, as early age of onset is highly associated with frequent cannabis use. 43, 44 We also found that shorter duration of cannabis use predicted more withdrawal symptoms. This could be because shorter-term users did not have tolerance to cannabis, as might be expected of longer-term or dependent users. These validators should be further addressed in future laboratory studies to establish more specific mechanisms. Finally, weakness/fatigue cannabis withdrawal symptoms in our study were associated with a family history of drug problems in the subset of frequent cannabis only users, while the depression/anxiety withdrawal symptoms were not. Further evidence of the familial nature of these two types of symptoms would contribute important information towards understanding their etiology.
