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".
4.2.1 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.
