The large-scale study, the largest review of medical cannabis to date, found no evidence that cannabis effectively treats anxiety, depression or PTSD. However, millions of people use it for these reasons. Researchers warn that cannabis can worsen mental health, increase risks such as psychosis and addiction, and delay proven treatment. Some limited benefits have been seen in insomnia and autism, but the evidence is weak. The findings support calls for tighter oversight of the growing use of cannabis.