Cannabis, also known as marijuana (from the Mexican Spanish marihuana), and by other names,a[›] is a preparation of the Cannabis plant intended for use as a psychoactive drug and as medicine. Pharmacologically, the principal psychoactive constituent of cannabis is tetrahydrocannabinol (THC); it is one of 483 known compounds in the plant, including at least 84 other cannabinoids, such as cannabidiol (CBD), cannabinol (CBN), tetrahydrocannabivarin (THCV). and cannabigerol (CBG).
Contemporary uses of cannabis are as a recreational drug, as religious or spiritual rites, or as medicine; the earliest recorded uses date from the 3rd millennium BC. In 2004, the United Nations estimated that global consumption of cannabis indicated that approximately 4% of the adult world population (162 million people) used cannabis annually, and that approximately 0.6% (22.5 million) of people used cannabis daily. In the United States, cannabis is the most commonly used illicit drug; 5.1% of Americans said they used marijuana in the past 30 days. In 1977, 38% of 12th graders reported using cannabis in the past month; in 2011, 23% of the same age group reported using cannabis in the same time span. Since the early 20th century cannabis has been subject to legal restrictions with the possession, use, and sale of cannabis preparations containing psychoactive cannabinoids currently illegal in most countries of the world; the United Nations has said that cannabis is the most-used illicit drug in the world.
Cannabis has psychoactive and physiological effects when consumed. Some alternative media sources report that minimum amount of THC required to have a perceptible psychoactive effect is about 10 micrograms per kilogram of body weight.[medical citation needed] Aside from a subjective change in perception and, most notably, mood, the most common short-term physical and neurological effects include increased heart rate, increased appetite and consumption of food[medical citation needed], lowered blood pressure, impairment of short-term and working memory,psychomotor coordination, and concentration. Long-term effects are less clear. In humans, relatively few adverse clinical health effects have been documented from chronic cannabis use.[medical citation needed]