marijuana is smoked. Smoking Health effects of smoking Some data on the correlation of an increase in the incidence of lung cancer and cannabis smoking are conflicting. A systematic review evaluating 19 studies from 1966 to 2006 found no significant tobacco-adjusted association between cannabis smoking and lung cancer development despite evidence of precancerous histopathologic changes of the respiratory mucosa. Cannabis smoke was listed as a cancer agent in California in 2009. Cannabis smoke contains many of the same carcinogens as tar from tobacco smoke. A 2012 literature survey by the British Lung Foundation identified cannabis smoke as a carcinogen and also found awareness of the danger was low, with 40% of under 35s thinking that cannabis (when smoked) was not harmful. Other observations include lack of research on the effect of cannabis smoke alone due to common mixing of cannabis and tobacco and frequent cigarette smoking by cannabis users; low rate of addiction compared to tobacco; and episodic nature of cannabis use compared to steady frequent smoking of tobacco. A 2013 literature review said that exposure to cannabis had biologically based physical, mental, behavioral and social health consequences and was "associated with diseases of the liver (particularly with co-existing hepatitis C), lungs, heart, and vasculature". The authors cautioned that "evidence is needed, and further research should be considered, to prove causal associations of marijuana with many physical health conditions". Materials Disposable materials Disposable materials are often used in places where cannabis is illegal. A roach is the remains of a joint, blunt or roll up cigarette after most of it has been smoked. Joint Joint is a slang term for a cigarette filled with cannabis instead of tobacco. Alternatively, mainly in Europe, joints may contain tobacco (commonly dubbed "a spliff", but not to be confused with the Jamaican term Spliff, which refers to a large joint) or various non-addictive herbs. Sometimes a joint will contain kief or hashish; hashish can be heated and made to crumble before placement within the joint. Specially manufactured rolling papers are most often used in industrialized countries; however, recycled brown paper and newspaper are commonly used in the developing world. Modern papers are now made from a wide variety of materials including rice, hemp, soy, and flax. A joint typically contains 250–750 mg net weight of cannabis and/or fillers. Blunt A blunt is cannabis rolled with a cigar wrapper (usually tobacco leaf, which contains nicotine).