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4.1 Routes of administration

4.1.1 Most cannabis in the UK is consumed in hand-rolled cigarettes ("joints", "reefers" or "spliffs") combined with tobacco, accounting for over 70% of consumption . Herbal cannabis is frequently smoked without added tobacco, accounting for about 5% of consumption, or smoked in pipes (16%). Either herbal cannabis or resin may be eaten by itself or in other food (4%). (By contrast, the most common form of marijuana consumption in the USA is the neat rolled cigarette). Cannabis resin accounts for around 60% of the total used, imported cannabis around 10%, and domestically-produced cannabis around 30%. Cannabis oil accounts for a small fraction of one percent of the market.

4.1.2 Cannabis can be smoked with or without tobacco in a pipe or water pipe ("bong"). Other methods of smoking without tobacco include "hot knives" where a piece is crushed between red-hot blades and the vapours inhaled, or a coal is left to smoulder and the smoke collected in a glass, bottle or bucket before inhalation. Although smoking around 2-6 pipes per day would represent average consumption, a significant minority of users will consume in excess of 15 pipes per day.

4.1.3 Cannabis resin "joints" with tobacco contain on average approx. 150mg, resin, range around 50mg to 350mg. Herbal cannabis "joints" with tobacco contain an average of around 200mg cannabis, although amounts vary considerably. A minority of herbal cannabis users, mainly those who grow their own, smoke cannabis in neat cigarettes containing 500mg to 1g.

4.1.4 Cannabis Oil when smoked is commonly smeared on to a cigarette paper and tobacco then enclosed, or a drop is mixed with tobacco before the material is rolled in the paper. As it is inconvenient to smoke, many users of oil prefer to use it in cooking.

4.1.5 Use in oral preparations is limited by the lipid solubility of THC and other cannabinoids, requiring use of fats or alcohol to emulsify the drug into an edible form. The main problem is the risk of overdose, as the effects are slow to develop but can be intense.

4.1.6 The BMA report on therapeutic uses referred to particulate studies of cannabis and tobacco cigarettes, originally published in 1982 by the National Institute on Drug Abuse in the USA. The cannabis used was of poor quality by today"s standards (approx. 1% THC). It is by no means clear whether the composition of smoke from high potency cannabis would be similar to the cannabis used for that study, and I am unaware of any studies as to the content of smoke arising from cannabis resin in pipes or resin/tobacco reefers. Such research should be considered a priority.

4.1.7 A recent study of water pipes and other smoking paraphernalia found that an unfiltered pure cannabis cigarette was as effective a method of delivery as any of the devices tested, using criteria of THC dose to particulates and other potential carcinogens. However, one of the vaporisers tested did perform similarly. Most water pipes absorbed too much THC, leading the user to smoke more to achieve the desired "high".

4.2 Smoking

4.2.1 Methods of ingestion vary widely in prevalence across the globe. 77.6% of cannabis use in the UK is by smoking joints, the majority of which contain tobacco. Smoking in all its forms accounted for some 96.2% of our samples of methods.

4.2.2 Whether cannabis smoke is more or less harmful than tobacco smoke is an argument that constantly rages between the extremes of the drug debate. It is, however, irrelevant, as all research indicates that both substances contain a variety of carcinogens such as polycyclic aromatic hydrocarbons as well as other noxious substances.

4.2.3 The preference for smoking as a method of ingestion may be a result of several different factors. Smoking cannabis produces noticeable effects far more immediately than when it is eaten or drunk. It is also consumed in small, discrete amounts over a mildly extended period of time. The dosage is easily controlled by self-titration. In contrast eating cannabis, whether raw or in preparations, predicates towards consuming the entire uncertain dosage at once. This can easily result in the consumption of less or more than required to achieve the desired effects.

4.2.4 Traditionally cannabis users have viewed the health risk of each method of ingestion to run from greatest to least in the following order: joint with tobacco, neat joint, pipe, water pipe, vaporiser and eaten. This has been based on observable differences in each method and on "common sense".

4.2.5 In a joint the entire matter is inhaled leaving very little residue other than a fine ash. This indicates that the user is ingesting all the compounds from the drug as well as those from the paper and tobacco. The smoke inhaled is of a reasonably high temperature, which increases as the joint is consumed and the cooling effect of the journey from tip to mouth is reduced.

4.2.6 Smoking cannabis in pipes immediately removes tobacco compounds, as well as those contained in the paper. A proportion of the tars and oils remain fixed to the inner surfaces of the pipe.

4.2.7 Water pipes have several advantages over other forms of smoking since a percentage of the tars and particulate matter are retained in suspension as the vapour passes through the reservoir, as well as on the inner surfaces of the pipe. Fairbairn's group postulated that, since the natural inhibitor of THC action which is present in cannabis is water soluble, the use of water pipes will reduce its effects and in consequence maximise the psychoactive effect.

4.2.8 More recently the UK and US cannabis scenes have witnessed a growth in popularity of the vaporiser. Vaporisers are designed to heat the drug to the point at which the volatile cannabinoids are released without the plant material combusting. The desired result is to maximise the cannabinoids ingested without necessarily inhaling the particulates and tars.

4.2.9 Recent harm reduction research in America has thrown doubt on the traditional beliefs concerning the health risks associated with the various forms of inhalation. Seven devices (a filtered joint, an unfiltered joint, a portable water pipe, a traditional bong, a battery operated water pipe, a vaporiser and a hybrid water pipe/vaporiser) were tested, and the amounts of cannabinoids and solid particulates delivered to the user were measured and compared. In all cases the devices used neat marijuana supplied by NIDA with a potency of 2.3% THC.

4.2.10 The researchers were surprised to discover that the water pipes were consistently outperformed by the unfiltered joint (with a ratio of 1 part cannabinoids to 13 parts tar) The best performing water pipe was matched by the filtered joint, both devices producing about 30% more tar per cannabinoids. The two vaporisers did better than the unfiltered joint, although the hybrid device only just so, while the pure vaporiser outperformed the joint by some 25%. However, the vaporiser produced much lower levels of THC and higher levels of non-psychoactive CBN than the other devices. While this might not be a problem for users whose primary purpose is medicinal the study was intended to aid harm reduction in recreational users, and so results were recomputed to provide a THC to particulates ratio. When this was done the pure vaporiser fell to a position below that of the unfiltered joint.

4.2.11 The researchers point out that no readings of the noxious gases produced in the burning of marijuana were measured. Gases such as hydrogen cyanide, volatile phenols, aldehydes and carbon monoxide are known to occur. Since water filtration has previously been shown to be effective at removing some of them, the team concluded that further research may indicate that the use of water pipes may offer a net health benefit.

4.2.12 In addition, THC transfer rates were computed to establish the smoking efficiency of the various devices. Again, the unfiltered joint performed surprisingly well and, along with the bong and the portable water pipe, delivered about 20% of the THC to the user. All the other devices had transfer rates less than one third as efficient as the top three devices.

4.2.13 The research was carried out in terms of harm reduction, with a view to reducing the amount of carcinogenic tars inhaled rather than non-carcinogenic cannabinoids. In consequence, the researchers reached the conclusion that the higher the ratio of THC to tars the better, since users normally regulated their doses based on how profound an effect they achieved rather than on the amount of cannabis consumed. Therefore, if a greater degree of "high" were obtained from a smaller amount of cannabis then the amount smoked would decrease proportionally.

4.2.14 This reasoning also leads to the conclusion that the higher the potency of the cannabis smoked the lower the amount smoked. The results were obtained with 2.3% THC cannabis, while commonly available cannabis on the street has higher levels of THC with no increase in tar levels. Had cannabis with a potency of 12-14% THC been used then, the researchers suggested, users would be able to reduce their inhalation of tar by a factor of five while still achieving the desired level of high.


4.3 Oral Use and Dosages

4.3.1 When cannabis is taken orally, the effects take much longer to develop and peak, (1-2 hours, as opposed to a few seconds), and subside more slowly. THC, not being water-soluble, must be taken with some fat, oil or alcoholic carrier to permit absorption into the blood. It is generally considered that up to three times as much cannabis is required when taken orally compared to smoking the drug, as evidenced by the equivalent analgesic efficacy of THC doses of 20mg taken orally and 7.5mg smoked.

4.3.2 According to Parke-Davis a 70kg man should require 4mg/kg, or 280mg (solid extract) as an effective dose. This would be consistent with approximately one gram of quality cannabis tops (5-10% potency). Animal studies have suggested higher effective doses.

4.3.3 One would expect the user to achieve the most appropriate dose level over time through experience of the desired and the adverse effects. Apart from potentially disturbing psychological effects, the risks to physical health from overdose are not significant.

4.3.4 The BMA have called for further research on appropriate dosage regimens and routes of administration for cannabinoids. Oral preparations, aerosol inhalants, rectal suppositories and skin patches have been discussed.

4.3.5 The economic cost of producing synthetic THC (Dronabinol) is considerably higher than the cost of producing high-potency plants, solvent extraction of the THC and other cannabinoids, and separation via column chromatography. If licensing of preparations for medicinal use is to be considered, these should not be restricted to synthetic products where natural alternatives of known cannabinoid content can be provided more cheaply.

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