British scientists have found how a substance in the cannabis plant acts in the brain to reduce abnormal activity in patients at risk of psychosis. Their findings suggest that the substance could be used in a possible treatment for the condition. Cannabis, also known as marijuana, is illegal to grow, sell or use in many countries. Using powerful forms of cannabis can increase a person’s chances of developing psychosis. But the substance the researchers studied, the chemical cannabidiol, appears to have the opposite effect. Cannabidiol, or CBD, is non-intoxicating. That means it is unlike drugs or alcoholic products, which can affect the user’s judgement or behavior. CBD is the same cannabis substance that has also been shown to help patients with epilepsy, a disorder of the nervous system. This led to the approval in the United States of a cannabis-based drug, a specially processed form of CBD, in June.