Marijuana is the most commonly used illegal substance in the US and Britain. The evidence suggests it may not be as harmless as many of us would like to think. The risk of developing schizophrenia is given as one in a hundred, and if you smoke pot, that risk increases to 1.4 in a hundred.
New British research, published in the medical journal The Lancet, thoroughly explores the correlation between smoking weed and schizophrenia. The researchers find that smoking pot causes a 40% increase in the smoker's risk of developing psychotic mental illness with symptoms such as paranoia, hearing voices and seeing things. The risk increases with the level of usage. The Lancet report estimates that 14% of 15 to 34-year-olds currently suffering schizophrenia are ill because they smoked cannabis, a figure previously thought to be between 8% and 10%.
One researcher acknowledged that “It is possible that the people who use cannabis might have other characteristics that themselves increase risk of psychotic illness”. I agree with this. I think that people who smoke pot are often self-medicating for something. Same as any substance. So potsmokers could be predisposed to go nuts before they ever start puffing.
Here are the links I read: