Marijuana seems to help some patients with migraine and cluster headaches. However a new study suggests that it has more negative effects than previously thought. We know that smoking pot causes lung problems and risks serious damage to various organs due to possible impurities. A recent report in the Proceedings of the National Academy of Sciences shows that regular cannabis use is harmful to health. Adolescents are beginning to use marijuana at younger ages, and more adolescents are using it on a daily basis. This study showed that persistent use of marijuana leads to neuropsychological decline. Researchers from Duke University, England and New Zealand examined records of 1,037 individuals who were followed from birth to age 38. Marijuana use was determined in interviews at ages 18, 21, 26, 32, and 38. Neuropsychological testing was conducted at age 13, before initiation of marijuana use, and again at age 38. Persistent use was associated with neuropsychological decline, including IQ, even after taking into account years of education. Persistent marijuana users reported noticing more cognitive problems. Impairment was strongest among those who started using marijuana in adolescence and the more persistent was the use the greater was the cognitive decline. Stopping marijuana use did not fully restore neuropsychological functioning and IQ among those who started its use in adolescence. This study suggests that cannabis has a toxic an persistent effect on the adolescent brain.