<unk>  were made for<unk> research focusing on tetrahydrocannabinol (THC),<unk> receptors, and the endocannabinoids that activate them in the body.<unk>  were needed partly due to legal restrictions on natural<unk> , which make them difficult to obtain for research. Many have been useful because they bind selectively to either the CB1 or CB2 receptors, whereas THC has a similar affinity for both. Tritium-labelled<unk>  such as CP-55,940 were instrumental in discovering the<unk> receptors in the early 1990s. Some early<unk>  were also used clinically. Nabilone, a first generation<unk>  THC analog, has been used as an antiemetic to combat vomiting and nausea since 1981.<unk>  THC (marinol, dronabinol) has been used as an antiemetic since 1985, and an appetite stimulant since 1991, although<unk>  THC is often not listed among the<unk> " but as a<unk>  phytocannabinoid." In the early 2000s,<unk>  began to be used for recreational drug use in an attempt to get similar effects to cannabis. Because<unk> molecular structures differ from THC and other illegal<unk> ,<unk>  were not technically illegal. Since the discovery of the use of<unk>  for recreational use in 2008, some<unk>  have been made illegal, but new analogs are continually synthesized to avoid the restrictions.<unk>  have also been used recreationally because they are inexpensive and are typically not revealed by the standard marijuana drug tests. Unlike nabilone, the<unk>  found being used for recreational use did not have any documented therapeutic effects.
Synthetic cannabinoids
Substituted amphetamine
Psychedelic drug
Amphetamine type stimulant
Heroic medicine
Querulant
Byzantine medicine
Substituted tryptamine