Marijuana

Marijuana is a mixture of dried, shredded leaves, stems, seeds and flowers of the hemp plant (Cannabis sativa). Other forms of cannabis include sinsemilla, hashish and cannabis oil. All forms contain THC (delta-9-tetrahydrocannabinol), which is the main active ingredient in marijuana.

Marijuana and cancer 

Some evidence suggests long-term use of marijuana can lead to cancers of the head, neck, lung and throat. However, the quality of this research is not as strong or as comprehensive as the evidence on tobacco and cancer. The fact that many people who smoke marijuana also smoke tobacco or mix the marijuana with tobacco makes it difficult to determine the strength of the association. Also, because there is no standard amount of THC (the main active ingredient in marijuana) in every marijuana cigarette, it is difficult to compare results across different studies. 

Some studies indicate that inhaled smoke from any burning plant product causes the same type of damage to lungs and throat as cigarette smoke. People who smoke marijuana tend to inhale more smoke per puff and hold it in their lungs for as much as four times longer than people who smoke tobacco cigarettes. This means that smoking 3 to 4 marijuana cigarettes per day can expose you to roughly the same amount of smoke as 20 tobacco cigarettes. 

Marijuana users and people exposed to second-hand marijuana smoke may have many of the same health problems as people exposed to cigarette smoke, including an increased risk of cancer.