Cannabis, cannabis resin and cannabinoids
Herbal cannabis (marijuana) means all parts of the plant Cannabis sativaL., but excludes the seeds and mature woody stalk material. Cannabis sativaL., which can be grown in all parts of the world, is an annual plant and attains a height of 1 to 5 m (Fig. 1). In tropical climates it grows readily outside, but in temperate climates such as the UK cultivation is typically carried out indoors to provide year-round supplies and to ensure good flowering. When it is planted for the production of hemp fibre and hemp oil, the stalks are crowded and without foliage except near the top of the plant. The varieties grown for commercial hemp production are typically selected to be low in cannabinoids the active substances. The wild-growing plant, in contrast, has numerous branches (Fig. 1). The resin of the plant occurs mainly in the flowering area, the leaves and the stem, particularly at the top of the plant. The greatest amount of resin is found in the flowering part. Up to the time of flowering, male and female plants produce resin nearly equally, but after shedding their pollen the male plants soon die. Female plants are selected for illicit cannabis production.
The leaves of Cannabis sativa L. are compound and consist of 5 to 11 separate leaflets, each characteristically hair covered, veined and with serrated edges (Fig. 1). Under microscopic examination, features characteristic for cannabis may be seen for herbal cannabis and cannabis resin:
• cystolithic hairs
• glandular hairs.
The cystolithic hairs contain a deposit of calcium carbonate at their base (Fig. 2). These hairs are mostly single cells. The glandular hairs trichomes) are most important since they contain and secrete the resin. They are short and may be unicellular or multicellular. The larger glandular hairs have a multicellular stalk with heads that contain 8 to 16 cells (Fig. 2). Cannabis herbal material (Fig. 3B) may be encountered in blocks of dried flowering tops and dried leaves. Cannabis resin (hashish) is a compressed solid made from the resinous parts of the plant (Fig. 3A). It is usually produced in 250 g blocks. Herbal cannabis imported into Europe may originate from West Africa, the Caribbean or South East Asia, but cannabis resin derives largely from either North Africa or Afghanistan. Cannabis has a characteristic odour which can aid in identification of the material. Cannabis and cannabis resin are normally mixed with tobacco and smoked, but can be ingested. The average ‘joint’ contains around 200 mg of herbal cannabis or cannabis resin. Cannabis oil (hash oil) is an extract of cannabis or cannabis resin and can contain up to 60% of cannabinoids.
Figure 1 Cannabis plants in cultivation. Note the characteristic leaves and the flowering tops which contain the highest proportion of THC. (Photograph: US Drug Enforcement Administration.)
Figure 2 (A) Photograph and (B) diagram of a glandular stalked trichome (left) and cystolithic non-glandular trichome (right). (Photo from The Medicinal Uses of Cannabis and Cannabinoids p. 26; courtesy of David Potter.)
Figure 3 (A) Cannabis resin (hashish); (B) herbal cannabis – dried flowering tops. (Photograph: US Drug Enforcement Administration.)
The main psychoactive compound in cannabis and cannabis resin is D9-tetrahydrocannabinol (∆9-THC) (Fig. 4A). Cannabinol (CBN) (Fig. 4B) and cannabidiol (CBD) (Fig. 4C) are among the other main components. Cannabinol is the major breakdown product of D9-THC and cannabinol is a precursor to D9-THC. The inter action with the active components in cannabis is via specific cannabinoid receptors (CB1 receptors in brain, lung, and kidney, and CB2 receptors in the immune system and in haematopoietic cells). These receptors are members of the G protein-coupled receptors. Binding of THC to the receptor results in inhibition of adenylate cyclase and in calcium channel inhibition and potassium channel activation. Administration of cannabis initially produces a feeling of euphoria and heightened sensory awareness and distortion of time, sound and colour which is followed by a feeling of relaxation.
Figure 4 (A) D9-Tetrahydrocannabinol; (B) cannabinol; (C) cannabidiol.
