Cannabis, also known as marijuana, marihuana, and ganja (from Sanskrit: गांजा gañjā, meaning "hemp"), among many other names, refers to any number of preparations of the Cannabis plant intended for use as a psychoactive drug. The most common form of cannabis used as a drug is the dried herbal form.
The typical herbal form of cannabis consists of the flowers and subtending leaves and stalks of mature pistillate or female plants. The resinous form of the drug is known as hashish (or merely as 'hash').

The major psychoactive chemical compound in cannabis is Δ9-tetrahydrocannabinol (commonly abbreviated as THC). At least 66 other cannabinoids are also present in cannabis, including cannabidiol (CBD), cannabinol (CBN) and tetrahydrocannabivarin (THCV) among many others, which are believed in influence the effects of THC alone.

Cannabis use has been found to have occurred as long ago as the third millennium B.C. In modern times, the drug has been used for recreational, religious or spiritual, and medicinal purposes. The United Nations (UN) estimated that in 2004 about 4% of the world's adult population (162 million people) use cannabis annually, and about 0.6% (22.5 million) use it on a daily basis. The possession, use, or sale of cannabis preparations containing psychoactive cannabinoids became illegal in most parts of the world in the early twentieth century. Since then, some countries have intensified the enforcement of cannabis prohibition, while others have reduced it.