Generally coming from dried marijuana leaves, cannabis is a smokable and ingestible substance that has been around for hundreds of years in a variety of different countries. It may even have been used as long as opium or alcohol. Cannabis' active ingredient is concentrated tetrahydrocannabinol (or THC), a compound also found in hashish (or hash). Although sometimes classified differently, cannabis psychoactive chemicals are actually hallucinogens.

The difference between cannabis preparations, LSD, and other hallucinogens is in the effectiveness of their dose; cannabis is very mild and must be taken in large quantities to produce the same effects as other hallucinogens. Another difference is that cannabis typically results in more sedation. Cannabis also causes impaired coordination and judgment which frequently results in motor vehicle accidents. Common physical and mental effects of hallucinogens and cannabis are mild euphoria, a rapid pulse, short-term memory impairment, and red eyes. Marijuana also produces chronic bronchitis, emphysema, angina (in people with cardiovascular disease because of the rapid heart rate that accompanies marijuana smoking) and lung cancer because it is smoked just like tobacco. The higher the THC (the active ingredient) quantity in marijuana, the higher the potency will be, as well as increased risk of toxicity. This is similar to PCP, which is stored in body fat and often has protracted effects in potent marijuana use. Extremely potent marijuana is grown in California, the Pacific Northwest, and Hawaii.