Cannabis is a flowering plant that can be used recreationally or medicinally. It contains the psychoactive chemical THC and other cannabinoids, which interact with neurotransmitters in the brain to produce a variety of effects. The drug is a popular substance in many countries around the world, and is the second most widely abused illicit drug after alcohol. It is found in the form of dried infructescences (buds), resin, and extracts including hash oil. Currently, it is illegal to grow or possess marijuana in most countries. However, the Agriculture Improvement Act of 2018, known as the Farm Bill, made it legal to grow hemp, a form of cannabis with low levels of THC and high amounts of cannabidiol (CBD), which is non-psychoactive and has been shown to have many medical benefits. FDA has approved two drugs that contain CBD to treat neuropathic pain associated with multiple sclerosis and nausea caused by chemotherapy.

Generally, sativa strains of cannabis tend to produce an energetic high, suitable for socializing or creative thinking, while indica strains have a heavier, more sedative effect. Hybrid strains, which combine sativa and indica parentage, can also produce a wide range of effects. When smoked or vaporized, THC enters the bloodstream and produces an immediate reaction in the brain. In comparison, edible preparations and tinctures are absorbed at a slower rate, and take thirty to sixty minutes to begin producing an effect.

Like other drugs of abuse, cannabis can have detrimental physical and psychological health effects. It can interfere with normal functioning and is addictive. People who use cannabis may have difficulty maintaining focus and concentration, and should avoid engaging in risky activities while under its influence. It can cause dizziness, disorientation, and changes in perception.