Cannabis smoking involves inhaling vapors released by heating the flowers and subtending leaves and stems of the Cannabis plants, known as marijuana. Alternatively, the cannabis plant flowers may be finely sifted producing kief, a powder especially rich in the oil-glands or trichomes which contain the highest amounts of cannabinoids. In exporting countries the kief is usually pressed under heat to form solid cakes of hashish, easily stored and shipped, which is widely marketed for smoking use. Cannabis is consumed recreationally to produce a feeling of relaxation or euphoria, medically (such as to relieve stress or suppress nausea), or inspirationally by inventors and artists in pursuit of creativity.
Smoking releases the main psychoactive chemical in cannabis, Δ9-tetrahydrocannabinol (THC), which is absorbed into the bloodstream via the lungs. It then mostly targets the brain, where it binds to cannabinoid receptors. The immune system also contains cannabinoid receptors and may modulate its function. The cannabinoid receptors receive the THC and other cannabinoids, leading to the feeling of a mental "high," which varies strongly by person. Studies have also found that the heating of cannabis (which can be achieved without the health hazards of combustion by means of a vaporizer) results in the production of additional THC from the decarboxylation of the non-psychoactive Δ9-tetrahydrocanabinoid acid (THCa).
While cannabis can be consumed orally, the bioavailability characteristics and effects of this method are different from smoking. The effect takes longer to begin, is typically longer-lasting, and can result in a more powerful psychoactive effect than expected.
Miniature smoking pipes, sometimes called pieces or bowls, are made of blown glass, metal fittings (except aluminum), ceramic, borosilicate, stone, wood, bamboo and other materials. Blown-glass pipes and bongs are often intricately and colorfully designed, containing materials that change color or become more vivid with repeated use.
- A narrow bowl (crater) with a top opening inner diameter of 5.5 mm (7/32") permits measured 25 mg loadings of pre-sifted cannabis and accurate control of the volume of heated air entering during lighting (about 200 °C / 392 °F). Through convection heating, the active chemicals are mostly vaporized rather than burned, maximizing THC production while minimizing exposure to combustion toxins.
- Installing a snugly nested mesh-#40 metal screen in the crater of the utensil protects against drawing small particles of herb down inside to clog the channel, and thus permits using a pre-sifted "one-toke" grade of cannabis with a uniform particle size which readily vaporizes out cannabinoids.
- Attaching a long flexible drawtube, such as those furnished on hookahs and vaporizers, (a) permits a clear view during the lighting operation and (b) gives vapors additional space to travel, cooling, before inhalation.
- "Vaporizing" with a one-hitter: by holding a heat source (such as a moderate lighter flame) about 2 cm below the opening of a narrow metal-headed utensil, while sucking continuously, a user can draw just enough heated air —but no flame— in upon a loading of pre-sifted herb particles or hashish to subject it to the preferred vaporization temperature of 140–200 °C. A visible darkening of the material (without catching fire) indicates drying, with successful harvesting of the desired volatile ingredients.
- Double toke: two long flexible tubes (like those furnished on hookahs and vaporizers) attached to exit-stems of one device permit partners sharing a single herb-loading to suck twice as slow and each receive half the heat, thus providing greater mildness (compensatory additional tokes served later).
Often in Morocco, Europe and the Middle East, users have facilitated lighting hashish by combining it with tobacco in a joint or spliff (also known as "Spinning", "Clip", "Batching", "Webacco", and "Amsterdam Style"). In India cannabis is combined with the mixture from unrolled Beedis, which are local blunts rolled with tobacco, herbs and condiments. At least one study has suggested that mixing cannabis with tobacco can lead to unintended nicotine dependence.
A major 2006 study compared the effects of tobacco and Cannabis smoke on the lungs. The outcome of the study showed that even very heavy cannabis smokers "do not appear to be at increased risk of developing lung cancer," while the same study showed a twenty-fold increase in lung cancer risk for tobacco smokers who smoked two or more packs of tobacco cigarettes a day. It is known that Cannabis smoke, like all smoke, contains carcinogens and thus has a probability of triggering lung cancer, but THC, unlike nicotine, is thought to "encourage aging cells to die earlier and therefore be less likely to undergo cancerous transformation." Cannabidiol (CBD), an isomer of THC and another major cannabinoid that is also present in cannabis, has been reported elsewhere to have anti-tumor properties as well.