No, prolonged use of cannabis has not been shown to negatively impact health. One of the first plants to be cultivated by humans, cannabis is useful for food, fiber, building materials, oil, medicine and many more applications. Any substance used in excess may cause problems (too much water can cause cerebral edema and death), but moderate use of cannabis has been shown to have many positive effects. Excessive smoking of the dried herb may cause mild bronchial irritation, but no increase in cancer or chronic obstructive pulmonary disease. Actually many of the challenges of aging; arthritis, dementia, changing hormones, depression, gastrointestinal distress, are well managed with cannabis. A bud a day keeps the doctor away.