Marijuana cigarettes (joints) contain more than 400 chemicals. One joint has up to four times as much cancer-causing tar as a regular filtered cigarette. Additionally, when a user smokes marijuana on a regular basis their body looses the ability to fight off infection. It can also increase the users heart rate leading to frequent chest colds. Research has shown that long-term marijuana use can increase the risk of developing certain mental illnesses.

New research has shown that individuals who smoke both cigarettes in addition to marijuana have a harder time trying to quit smoking (April 9 press release from the National Institute on Drug Abuse). In a study involving 431 adults, researchers at Johns Hopkins University found that cigarette smokers who used marijuana a month prior to the study were twice as likely to be smoking cigarettes at the 13-year follow-up. Also, researchers at UCLA's Jonsson Cancer Center are reporting, for the first time, that smoking marijuana may increase the risk of head and neck cancers.

The rapper Snoop Dogg, known for promoting marijuana has quit. He told MTV News that he had smoked marijuana daily for the past ten years but made the decision to stop because he wanted to start "feelin' good". This proves that even the heaviest marijuana smokers are able to quit if they so desire.