First, dosing of smoked marijuana remains unpredictable. And although much of the medical marijuana debate centers on the effects of single exposures, insufficient information exists regarding the effects of repeated exposures. Approximately 10% of people routinely using marijuana become addicted, with a higher incidence amongst adolescents. Tolerance and down-regulation of receptors have been documented with repeated marijuana use. A marijuana withdrawal syndrome has also been recognized, as has an association with psychosis.