Published in the February issue of the British Journal of Psychiatry, the paper by Prof. Heather Ashton highlights recent knowledge about the effects of cannabis on psychomotor and cognitive performance and health risks associated with the drug. The most potent psychoactive agent in cannabis, 'THC', has been isolated, synthesised and much studied. Now, with increasingly sophisticated cultivation and plant breeding, a joint may contain around 150mg of THC or 300mg if laced with hashish oil. The prevalence of cannabis use has increased markedly among young people over the past ten years. Extreme use can involve smoking up to 15 joints daily, exposing the user to several hundreds of milligrams of cannabis every 24 hours.
Cannabis affects almost every bodily system.
The 'high' comes on within minutes of smoking and then reaches a plateau lasting two hours or more, depending on dose. Whilst using cannabis undoubtedly gives pleasure to users, it can also produce severe anxiety and panic, paranoia and psychosis. These reactions are dose-related and more common among na ve users and people who are anxious or psychologically vulnerable. Episodes of schizophrenia may also be precipitated or aggravated by cannabis use. Cognition and psychomotor performance .