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high dose, the drug causes persistent, negative effects on verbal and visual memory, executive functioning, visuoperception, psychomotor speed, and manual dexterity. This level of use was shown to be associated with decrements in neurocognitive performance even after 28 days of abstinence. This persistence is generally linked to very heavy use of the drug. Although other reports suggest that neurocognitive and withdrawal affects do not extend beyond 25 days, performance and safety could conceivably be compromised even after a several-week period of abstinence.” There is also a significant combination effect when cannabis is consumed with alcohol, leading to a greater level of intoxication and motor control problems than when either substance is consumed alone. (Harris, 2016) Impairment may also be made worse when cannabis is consumed with other central nervous system (CNS) depressants such as benzodiazepines, barbiturates, opioids, antihistamines, or muscle relaxants (Health Canada, 2013). The National Health Service (NHS) (2016) in the United Kingdom indicates that data from a urine sample for THC reveal the following: • an occasional or first-time user would probably test positive up to four days after last using • a frequent user would probably test positive up to ten days after last using • a very heavy user could test positive up to one to two months after last using Therapeutic Uses of Cannabis and Cannabinoids In an evidence review, the National Academies of Sciences, Engineering and Medicine (2017) report the following conclusions about the therapeutic effects of cannabis and cannabinoids: Conclusive or substantial evidence that cannabis or cannabinoids are effective for: • the treatment of chronic pain in adults • as antiemetics (drugs taken to prevent or treat nausea and vomiting) in the treatment of chemotherapy-induced nausea and vomiting (oral cannabinoids) • for improving patient-reported multiple sclerosis spasticity symptoms (oral cannabinoids) Moderate evidence that cannabis or cannabinoids are effective for: • improving short-term sleep outcomes in individuals with sleep disturbance associated with obstructive sleep apnea syndrome, fibromyalgia, chronic pain, and multiple sclerosis (cannabinoids, primarily nabiximols) Limited evidence for: • increasing appetite and decreasing weight loss associated with HIV/AIDS (cannabis and oral cannabinoids) • improving clinician-measured multiple sclerosis spasticity symptoms (oral cannabinoids) 7 Canadian Centre for Occupational Health and Safety • improving symptoms of Tourettes syndrome (THC capsules) • improving anxiety symptoms, as assessed by a public speaking test, in individuals with social anxiety disorders (cannabiniol) • improving symptoms of post traumatic stress disorder (nabilone; a single, small fair quality trial) The National Academies of Sciences, Engineering and Medicine (2017) also report that there is substantial evidence of a statistical association between cannabis smoking and: • worsening respiratory symptoms and more frequent chronic bronchitis episodes (associated with long-term cannabis smoking), • increased risk of motor vehicle crashes, • maternal cannabis smoking and lower birth weight of offspring, and • development of schizophrenia and other psychoses, with the highest risk among the most frequent users. In Canada, commercial production and distribution of cannabis for therapeutic purposes is regulated under the Federal Access to Cannabis for Medical Purposes Regulations (SOR/2016-230). However, as Health Canada (2016a) states “There is no scientifically defined dose of cannabis for any specific medical condition.” and “Dosing remains highly individualized and relies greatly on titration (i.e., finding the right dose where potential therapeutic effects are maximized while adverse effects are minimized). The current available information suggests most individuals use less than 3 grams daily of dried marijuana, whether that amount is taken orally, inhaled, or a combination of both.” 8 Canadian Centre for Occupational Health and Safety LEGISLATIVE REQUIREMENTS Health and Safety As per occupational health and safety