"Essentially a herbal cannabinoid drug, the resin-secreting flowers of select varietals of the female cannabis plant contain approximately 6 dozen of different phytocannabinoids or plant-derived cannabinoids; these compounds are generally classified structurally as terpenophenolics with a 21-carbon molecular scaffold.24 Other compounds, such as terpenoids, flavonoids, and phytosterols, which are common to many other botanicals, are also produced by cannabis and have some demonstrated pharmacologic properties.25,26 The best known naturally produced analgesic cannabinoids generally found in highest concentrations are THC and cannabidiol. They occur in their acid forms in herbal cannabis and must be decarboxylated to become activated. Five minutes of heating at 200 to 210°C has been determined as the optimal conditions for maximal decarboxylation; with a flame, where temperatures of 600°C are achieved, only a few seconds are needed.27"

Source

Aggarwal, Sunil K., "Cannabinergic Pain Medicine: A Concise Clinical Primer and Survey of Randomized-controlled Trial Results," Clinical Journal of Pain (Philadelphia, PA: February 23, 2012), p. 2.
http://www.ncbi.nlm.nih.gov/p…