There are reports of people experiencing cannabis induced mental trauma, called 'cannabis psychosis' There is no evidence that cannabis use itself causes the use of harder drugs. All the evidence suggests that the cause is a personality type. Almost all heroin addicts started with cannabis. It is the first step on the road to hard drug addiction. There is no evidence that Cannabis smoke can contribute to lung damage or increase the risk of lung cancer.
Cannabis contains a significant amount of tar, and is usually smoked with tobacco.
Cannabis has been linked to at least five unnecessary deaths in the past ten years. Cannabis causes people to be calm and peaceful, unlike alcohol which often causes violence. Cannabis can cause paranoia, which in turn could cause violence.