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8. The therapeutic effects of cannabinoids
The following provisional conclusions can be drawn on the available evidence. First, there is good evidence for the therapeutic potential of THC as an anti-emetic agent. Although uncertainty exists about the most optimal method of dosing and the advantages and disadvantages of different routes of administration, there is sufficient evidence to justify it being made available in pure synthetic form to cancer patients. In the light of the recent development of more effective anti-emetic agents, it remains to be seen how widely used the cannabinoids will be. Second, there is reasonable evidence for the potential efficacy of THC in the treatment of glaucoma, especially in cases which have proved resistant to existing anti-glaucoma agents. Further research is clearly required, but this should not prevent its use under medical supervision in poorly controlled cases, provided patients make informed decisions about its use in the light of information about the possible health risks of long-term use. Third, there is sufficient suggestive evidence of the potential usefulness of various cannabinoids as analgesic, anti-asthmatic, anti-spasmodic, and anti-convulsant agents to warrant further basic pharmacological and experimental investigation, and perhaps clinical research into their effectiveness.
Despite the basic and clinical research work which was undertaken in late 1970s and early 1980s, the cannabinoids have not been widely used therapeutically, nor have further investigations been conducted along the lines suggested in the positive evaluations made by the Institute of Medicine (1982). This seems largely attributable to the fact that clinical research on the therapeutic use of cannabinoids has been discouraged by regulation and a lack of funding in the United States, where most cannabis research has been conducted. The discouragement of therapeutic research, in turn, derives from the fact that THC, the most therapeutically effective cannabinoid, has the psychoactive effects sought by recreational users. In opposing the therapeutic uses of cannabinoids, some researchers have used double standards in appraising efficacy and safety, setting unreasonably high standards in assessing the evidence on the comparative therapeutic safety and efficacy of cannabinoids and existing agents. The application of the same demanding standards to existing agents for the candidate diseases, and more generally, to existing psychoactive drugs that are widely used in medical practice, would denude the pharmacopoeia. The recent discovery of the cannabinoid receptor may help to overcome some of the resistance to research into the therapeutic uses of cannabinoids, by holding out the prospect that the psychoactive effects of the cannabinoids can be disengaged from their other therapeutically desirable effects.