The health and psychological consequences of cannabis use - chapter 4

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4. Cannabis the drug

4.3 Forms of cannabis

The concentration of THC varies with the forms in which cannabis is prepared for ingestion, the most common of which are marijuana, hashish and hash oil. Marijuana is prepared from the dried flowering tops and leaves of the harvested plant. Its potency depends upon the growing conditions, the genetic characteristics of the plant and the proportions of plant matter. The flowering tops and bracts (known as "heads") are highest in THC concentration, with potency descending through the upper leaves, lower leaves, stems and seeds. Some varieties of the cannabis plant contain little or no THC, such as the hemp varieties used for making rope, while others have been specifically cultivated for their high THC content, such as "sinsemilla".

Marijuana may range in colour from green to grey or brown, depending on the variety and where it was grown, and in texture from a dry powder or finely divided tea-like substance to a dry leafy material. The concentration of THC in a batch of marijuana containing mostly leaves and stems may range from 0.5-5 per cent, while the "sinsemilla" variety with "heads" may result in concentrations from 7-14 per cent.

The potency of marijuana preparations being sold has probably increased in the past decade (Jones, 1987), although the evidence for this has been contested (Mikuriya and Aldrich, 1988).

Hashish or hash consists of dried cannabis resin and compressed flowers. It ranges in colour from light blonde/brown to almost black, and is usually sold in the form of hard chunks or cubes. The concentration of THC in hashish generally ranges from 2-8 per cent, although it can be as high as 10-20 per cent. Hash oil is a highly potent and viscous substance obtained by using an organic solvent to extract THC from hashish (or marijuana), concentrating the filtered extract, and, in some cases, subjecting it to further purification. The colour may range from clear to pale yellow/green, through brown to black. The concentration of the THC in hash oil is generally between 15 per cent and 50 per cent, although samples as high as 70 per cent have been detected.