Cannabis smoking is the inhalation of smoke or vapors released by heating the flowers, leaves, or extracts of cannabis. Smoking releases the main psychoactive chemical in cannabis, Δ9-tetrahydrocannabinol (THC), which is absorbed into the bloodstream via the lungs.
Apart from being smoked and vaporized, cannabis may be consumed orally or applied to the skin; the bioavailability characteristics and effects of smoking and vaporizing cannabis differ from other consumption methods in having a more rapid and predictable onset of effect.
Joint is a slang term for a cigarette rolled using cannabis. Cannabis joints are mostly either made with pure herbal cannabis or with cannabis mixed with tobacco or various non-addictive herbs. Hashish requires a filler as it will not burn alone in a joint. Rolling papers are the most common rolling medium among industrialized countries; however, 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, and flax. A joint can range in size, typically containing between 250–750 mg net weight of cannabis and/or fillers.
Pipes made for smoking cannabis, sometimes called pieces or bowls, are made of a variety of materials, including blown glass, metal fittings, ceramic, Borosilicate glass, stone, wood, bamboo and other materials. Subtypes include one-hitters, bubblers, chillums, glass blunts, corn cob pipes, and standard hand pipes. Pipes vary greatly in shape and materials, and most are handmade. The common thread between them is having a screened receptacle of some sort, a "stem" (which may be a long flexible tube as on hookahs and vaporizers), and a "mouthpiece". The smoking material is placed in the receptacle and affected with a heat source while air is drawn through the bowl and stem to the user.
A bong, is similar to a pipe, only it has a water-chamber  through which cannabis smoke passes prior to inhalation and a wide "mouth" typically around 3.8–5.1 cm (1.50–2.01 in) in diameter. Users fill the bong with water, sometimes also adding ice or other substances in place of water in order to cool the smoke. Until recently it was widely believed that using a bong was healthier than a pipe or joint, while studies have shown the opposite, that the amount of psychoactive chemical filtered is greater than the harmful particles. Some bongs have a "choke" or "carb", a small hole usually located on the side of the bowl above water level, used to clear the pipe of smoke or to conserve material by stopping burning when enough smoke has been created.
A gravity bong (also known as a grav, bucket, or submarine) is a hydropneumatic device used for smoking cannabis. One variant consists of a bucket of water in which is typically placed a bottle with the bottom cut off, such as a 2-litre PET soft drink bottle. Some kind of cap or screen is rigged over the mouth of the bottle and filled with hash or cannabis. A flame is then held near enough to heat the drug while the bottle is slowly raised out of the water, creating a negative gauge pressure inside the bottle, drawing smoke from the heated cannabis—along with air—into the vacuum. The cap or screen is removed once the bottle is almost full, the user's mouth is placed over the mouth of the bottle and the bottle pushed back down into the water, causing the pressure to rise and forcing the smoke into the lungs. There are many variants on this basic premise, such as using a large water cooler tank in lieu of a soft drink bottle.
Similar to a gravity bong, a waterfall bong utilizes both a bottle and a cap or screen rigged over the bottle's mouth to hold cannabis. In this case, however, the bottle—which has one or several covered holes bored at the bottom—is filled with water before the cannabis is loaded. The holes are then uncovered, evacuating the water. When heat is applied to the drug, the resultant smoke is forced into the bottle with negative pressure, as with the gravity bong. Once the water is evacuated, the smoke can be inhaled from the bottle. Variations on this concept are also used.
Health effects of smoking
Studies regarding cancer risk
As of 2012, there is conflicting data on the correlation of an increase in the incidence of lung cancer and cannabis smoking. 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. Some studies indicate increased rates of cancer and others do not. The studies do indicate increased prevalence of pre-cancerous changes in the user's airways.
In the largest study of its kind, researchers found no cancer-cannabis connection. Donald Tashkin, a pulmonologist at University of California, Los Angeles who studied marijuana for 30 years, "hypothesized that there would be a positive association between marijuana use and lung cancer, and that the association would be more positive with heavier use". Instead, the study found "no association at all, and even a suggestion of some protective effect". The study, which involved a large population sample (1,200 people with lung, neck, or head cancer, and a matching group of 1,040 without cancer) found no correlation between marijuana smoking and increased lung cancer risk, with the same being true for head and neck cancers as well. The results indicated no correlation between long and short-term cannabis use and cancer, indicating a possible therapeutic effect. Extensive cellular studies and some studies in animal models suggest that THC or cannabidiol has antitumor properties, either by encouraging programmed cell death of genetically damaged cells that can become cancerous, or by restricting the development of the blood supply that feeds tumors, or both.
A 2012 literature survey by the British Lung Foundation identified cannabis smoke as a carcinogen and also found awareness of the danger was low compared with 40% of under 35s thinking that cannabis was not harmful. Other observations include increased risk from each cigarette due to drawing in larger puffs of smoke than cigarette smokers and holding the smoke in for longer; 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. Professor David Nutt, a UK drug expert, points out that the study cited by the British Lung Foundation has been accused of both "false reasoning" and "incorrect methodology". Further, he notes that other studies have failed to connect cannabis with lung cancer, and accuses the BLF of "scaremongering over cannabis".
In 2012, a 20 year study of pulmonary function and marijuana exposure concluded that "occasional use (1 joint a day for 7 years or 1 joint/week for 49 years) of marijuana for these or other purposes may not be associated with adverse consequences on pulmonary function". It also concluded that the findings do suggest an accelerated decline in pulmonary function with heavy use and a resulting need for caution and moderation when marijuana use is considered."
A 2008 study found that asymmetrical bullous lung disease occurs in marijuana smokers approximately 20 years earlier than tobacco smokers. Although the study concluded marijuana caused the bullous disease, they failed to account for confounding variables (as all 10 participants have a history of cigarette smoking) so the notion that cannabis use caused is far from conclusive. 
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