Cannabis has a lifetime risk for users to develop dependence of 9% compared with 67.5% for nicotine and 22.7% for alcohol52; it may be as high as 17% in those initiating cannabis use in early adolescence and gradually declines with age of onset of use.
A recent study reported a higher rate of adverse events among persons using cannabis for pain for 1 year at an average dose of 2.5 g herbal cannabis with 12.5% THC than that of control subjects, but not higher for serious adverse events.
http://www.sciencedirect.com/science/article/pii/S1526590016005435