A major safety concern associated with medical cannabis is the possibility of medical use encouraging or transitioning into recreational use, which is associated with side effects that range from acute to chronic. Acute effects include intoxication, impaired cognition and motor function, elevated heart rate, anxiety, and psychosis in predisposed individuals. Chronic effects include bronchitis (from smoked cannabis), psychological cannabis dependency, loss of motivation, and cognitive deficits. By and large these effects seem to disappear on abstinence.
Medical cannabis may be riskier and perhaps contraindicated if a patient has a personal or family history of psychosis, unstable cardiac disease, and lung disease. Medical cannabis users are advised by physicians not to use tobacco, either alone or mixed with cannabis. They also are advised not to drive or operate machinery while initiating or changing doses and if impaired by the drug. Apart from possible synergistic effects of cannabis with other psychotropic medications, such as sedatives and hypnotics, there are no known major drug-drug interactions.