Cannabis

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Abstract
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.