– Psychosis can be induced by drugs or can be “drug assisted”. Some stimulating drugs, like amphetamines, can cause psychosis, while other drugs, including marijuana, can trigger the onset of psychosis in someone who is already at increased risk because they have “vulnerability”.
It is also believed that some drugs such as amphetamines and cocaine can cause a condition known as a drug-induced psychosis. This psychosis can last up to a few days, and is often characterized by hallucinations, delusions, memory loss and confusion. This usually results from prolonged or heavy street-drug use; and it responds well to treatment.
Cannabis and Psychosis – information on why marijuana/pot/hash/cannabis is risky for people who have psychosis or are at risk for psychosis
Marijuana use increases risk for psychosis by 40% – An article by Theresa H.M. Moore, MSc, from the University of Bristol in the United Kingdom, and colleagues was published in the July 28 issue of The Lancet. Moore compared the results of several research studies that followed people over a period of time (systematic review of longitudinal studies). She found that there is enough new evidence that the use of cannabis (marijuana) increases the risk for later psychotic illness by roughly 40%.