Tetrahydrocannabinol, abbreviated THC, is a cannabinoid identified in cannabis and is its principal psychoactive constituent. First isolated in 1964, in its pure form, it is a glassy solid when cold, and becomes viscous and sticky if warmed. Synthetically prepared THC, officially referred to by its INN, dronabinol, is available by prescription in the U.S. and Canada under the brand name Marinol. The mechanism of action of THC is not completely understood. It is thought that cannabinoid receptors in neural tissues may mediate the effects of cannabinoids. Animal studies suggest that Marinol's antiemetic effects may be due to inhibition of the vomiting control mechanism in the medulla oblongata. A literature review on the subject concluded that "Cannabis use appears to be neither a sufficient nor a necessary cause for psychosis. It is a component cause, part of a complex constellation of factors leading to psychosis." Likewise, a French review from 2009 came to a conclusion that cannabis use, particularly that before age 15, was a factor in the development of schizophrenic disorders. An aromatic terpenoid, THC has a very low solubility in water, but good solubility in most organic solvents, specifically lipids and alcohols. The presence of these specialized cannabinoid receptors in the brain led researchers to the discovery of endocannabinoids, such as anandamide and 2-arachidonoyl glyceride (2-AG). THC targets receptors in a manner far less selective than endocannabinoid molecules released during retrograde signalling, as the drug has a relatively low cannabinoid receptor efficacy and affinity. In populations of low cannabinoid receptor density, THC may act to antagonize endogenous agonists that possess greater receptor efficacy. THC is a lipophilic molecule and may bind non-specifically to a variety of receptors in the brain and body, such as adipose tissue. Dronabinol is only found in individuals that have used or taken this drug. It is extracted from the resin of Cannabis sativa (marijuana, hashish). The isomer delta-9-tetrahydrocannabinol is considered the most active form, producing the characteristic mood and perceptual changes associated with this compound. In the United States, Marinol has been rescheduled from Schedule II to Schedule III of the Controlled Substances Act in 1999, reflecting a finding that THC had a potential for abuse less than that of cocaine and heroin. As a Schedule III drug, it is available by prescription and is considered to be non-narcotic and to have a low risk of physical or mental dependence. Marinol has been approved by the U.S. Food and Drug Administration (FDA) in the treatment of anorexia in AIDS patients, as well as for refractory nausea and vomiting of patients undergoing chemotherapy, which has raised much controversy as to why natural THC is still a Schedule I drug. Efforts to get cannabis rescheduled as analogous to Marinol have not succeeded thus far. In April 2005, Canadian authorities approved the marketing of Sativex, a mouth spray for multiple sclerosis patients, who can use it to alleviate neuropathic pain and spasticity. Sativex contains tetrahydrocannabinol together with cannabidiol and is a preparation of whole cannabis rather than individual cannabinoids. It is marketed in Canada by GW Pharmaceuticals, being the first cannabis-based prescription drug in the world (in modern times). In addition, Sativex received European regulatory approval in 2010. An analog of dronabinol, nabilone, is available commercially in Canada under the trade name Cesamet, manufactured by Valeant Pharmaceuticals. Cesamet has also received FDA approval and began marketing in the U.S. in 2006. It is a Schedule II drug.