Cannabis smoking involves inhaling vapors released by heating the flowers and subtending leaves 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 for its hallucinogenic effects for recreation, to produce a feeling of euphoria, medically to stimulate the appetite or to suppress nausea), or by inventors and artists in pursuit of creativity.^{[citation needed]}

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).