The National Academies of Sciences released a report on the health impacts of marijuana Thursday, confirming the existence of medical benefits and dispelling some long-held myths about the substance. The review of more than 10,000 scientific abstracts found, “There is conclusive or substantial evidence that cannabis or cannabinoids are effective” for the treatment of chronic pain in adults, chemotherapy-induced nausea and vomiting, and multiple sclerosis spasticity. The report also dispels several…