Marijuana actually contains more tar than tobacco cigarettes do. Cannabis tar has more cancer causing agents than tobacco tar. Also, people who smoke marijuana tend to inhale the smoke more deeply and hold it in their lungs longer. Since the smoke is in contact with the lungs for a longer amount of time than with cigarettes, it may cause even more damage. Alcohol is classified as a drug by the American Medical Association and the World Health Organization.
Alcohol affects the brain and nervous system and is considered a central nervous system depressant.