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Cannabis
  1. P Robson
  1. Chilton Clinic, Warneford Hospital, Oxford OX3 7JX
  1. Dr Robson.

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The robust weed christened Cannabis sativa by Linnaeus was humankind’s first non-food crop, and the medicinal and psychoactive properties of the resin exuded from the flowering tops of the female plants have been recognised for at least 8000 years.1 Today in Britain it is easily the most prevalent illicit drug; more than a third of A level students and over 50% of Oxford University undergraduates say they have sampled it.2 On the other hand, its classification within Schedule 1 of the Misuse of Drugs Regulations (1985) denies British doctors the right to prescribe it under any circumstances, and effectively rules out prospective research on human volunteers or patients which might clarify its properties, both beneficial and adverse.

Chemistry and pharmacology

Inhale deeply from a cannabis ‘spliff’ and your lungs will be on the receiving end of hundreds of chemicals, at least 60 of which are psychoactive. Early cannabinoids to be isolated were cannabinol in 1905 and cannabidiol 30 years later, but the seminal discovery was that of the main active ingredient, delta-9-tetrahydrocannabinol (THC) in 1964.3 Many related compounds were then identified which are characterised as aryl substituted meroterpenes.4 In 1988 a specific protein receptor for THC was identified in nerve cells5 and in 1992 Mechoulam and colleagues identified an endogenous ligand for this receptor which they called ‘anandamide’.6 In 1993 a second receptor was discovered in spleen macrophages.7 This ‘CX5’ receptor is not present within the central nervous system and its existence raises the possibility of developing compounds devoid of psychoactivity.

The natural role of the cannabinoid receptor and the anandamide system have yet to be delineated, but may be concerned with mood, memory and cognition, perception, movement, coordination, posture and skeletal muscle tone, sleep, thermoregulation, appetite, and immune response.8

Therapeutic potential

Cannabis has been used as …

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