Studies have shown that cannabis can produce a subtle impairment of attention, memory and the organisation and integration of complex information. The longer the cannabis use, the more pronounced the impairment. These impairments are subtle and it remains unclear whether these effects are reversed after an extended period of abstinence or what implications they may have for everyday functioning. In addition, researching this complex area is difficult : for example, there has been criticism of the adequacy of matching cannabis uses with control subjects in those studies on cognitive deficits in heavy cannabis users. There is no evidence for the scale of severe or debilitating impairment of memory, cognitive function and attention found with chronic heavy alcohol use. There is also no evidence that cannabis causes structural brain damage in humans.
