Like any substance, marijuana can be abused. The most common problem attributed to marijuana is frequent overuse, which can induce lethargic behavior, but does not cause serious health problems. Marijuana can cause short-term memory loss, but only while under the influence. Marijuana does not impair long-term memory. Marijuana does not lead to harder drugs. Marijuana does not cause brain damage, genetic damage, or damage the immune system. Unlike alcohol, marijuana does not kill brain cells or induce violent behavior. Continuous long-term smoking of marijuana can cause bronchitis, but the chance of contracting bronchitis from casual marijuana smoking is minuscule. Respiratory health hazards can be totally eliminated by consuming marijuana via non-smoking methods, i.e., ingesting marijuana via baked foods, tincture, or vaporizer.
A 1997 UCLA School of Medicine study (Volume 155 of the American Journal of Respiratory & Critical Care Medicine) conducted on 243 marijuana smokers over an 8-year period reported the following: "Findings from the long-term study of heavy, habitual marijuana smokers argue against the concept that continuing heavy use of marijuana is a significant risk factor for the development of chronic lung disease." "Neither the continuing nor the intermittent marijuana smokers exhibited any significantly different rates of decline in lung function as compared with those individuals who never smoked marijuana." The study concluded: "No differences were noted between even quite heavy marijuana smoking and nonsmoking of marijuana."
Marijuana does not cause serious health problems like those caused by tobacco or alcohol (e.g., strong addiction, cancer, heart problems, birth defects, emphysema, liver damage, etc.). Death from a marijuana overdose is impossible. In all of world history, there has never been a single human death attributed to a health problem caused by marijuana.