Cannabis In Medicine
Pot Night - The Book, Channel 4 Television, 1995
Dr Roger Pertwee
Cannabis and cannabinoids - what are they?
All preparations of cannabis come from the plant Cannabis sativa. This plant and the sticky resin it secretes are the only known botanical sources of a set of more than 60 compounds collectively called cannabinoids. One of these, delta-9 tetrahydrocannabinol (THC), is largely responsible for the characteristic pharmacological properties of cannabis.
THC (and therefore cannabis) can elevate mood, reduce the ability to concentrate and remember, and alter perception such that time seems to pass more slowly, colours seem more vivid and music more pleasant. It can also produce a feeling of relaxation and drowsiness. Effects such as these constitute the 'high' that has been exploited through the centuries for recreational and religious purposes. Many compounds with THC-like effects have now been designed and synthesised in the laboratory, and these are also now referred to as cannabinoids.
How does cannabis act?
The brain and certain other tissues contain an abundance of cannabinoid receptors. These are specialised sites that initiate particular changes in brain function whenever they are exposed to active cannabinoids such as THC. It is these changes that are thought to bring about many of the pharmacological effects of cannabis, including the 'high'.
Only compounds that possess cannabinoid properties can activate cannabinoid receptors. This raises the question of why the body contains these receptors as it seems most unlikely that they should have evolved so that people could experience the effects of cannabis. The answer is that the body can produce its own cannabinoids which probably function as chemical messengers. The first of these to be discovered was named anandamide after the Sanskrit word for 'internal bliss' (ananda).
In addition, some drugs can prevent cannabinoids from interacting with their receptors. Like the cannabinoids that activate cannabinoid receptors, these cannabinoid receptor blockers may well have important medical applications.
Is cannabis addictive?
Individuals who have taken cannabis for prolonged periods could find that they have developed a mild 'physical' addiction, in that they may experience transient, minor changes in mood, sleep, heart rate, body temperature, salivary flow, food intake and appetite if they stop taking the drug. Restlessness, tremor, mild nausea, hot flushes and sweating may also occur for a limitied time after cannabis is given up. However, individuals who take cannabis repeatedly are unlikely to become 'psychologically' addicted: present evidence indicates that giving up cannabis is not usually followed by any irresistible urge to begin taking the drug again. In this respect, cannabis is quite different from drugs such as heroin, cocaine or nicotine.
Does cannabis consumption encourage the use of other drugs?
There is no evidence that cannabis consumption will cause individuals to seek out and take other drugs - for example, heroin or cocaine - because they can produce a much stronger 'high'. Where a progression to other drugs does occur, it is most likely because people who wish to take cannabis have been forced into contact with illegal suppliers of such drugs.
Do cannabinoids have any beneficial effects
There is evidence that cannabis or individual cannabinoids will suppress some of the signs and symptoms of certain serious disorders. These include the raised pressure within the eye that occurs with glaucoma; the muscle stiffness and spasms and the impairment of bladder function caused by multiple sclerosis or spinal injury; the breathing difficulties of bronchial asthma; and the nausea and vomiting and the loss of both appetite and weight experienced by AIDS patients. Cannabinoids can also relieve moderate chronic pain. It is claimed that at least some of the beneficial effects of cannabinoids can be experienced by taking doses that are lower than those needed to produce a 'high'.
Although some clinical trials have already been carried out, much of the evidence supporting tha medical use of cannabinoids is anecdotal, and clearly more research is needed. At the same time, it is worth noting that as recently as 1971, it was permissable to prescribe cannabis for patients in this country, and that one synthetic THC-like compound, nabilone, can now be prescribed by hospital doctors to suppress the nausea and vomiting provoked by anti-cancer drugs.
Do cannabinoids have any harmful effects?
Cannabinoids are no different from any other group of drugs, prescribed or otherwise: they can be harmful. However, their known unwanted effects are no more severe or dangerous than those of drugs now available on prescription. In addition, although some groups of individuals are particularly at risk from the effects of cannabinoids (see below), this should not in itself preclude their use for medical purpose as it is not unusual for medical drugs to be suitable for some patients but to provoke unacceptable side-effects in others.
Because cannabinoids can produce serious adverse effects in some people, it is important that anyone considering the issue of cannabis decriminilisation or legalisation should distinguish between the supervised consumption of cannabinoid preparations for medical use and unsupervised recreational use of such preparations.
What are the known harmful effects of cannabinoids?
There is evidence that cannabinoids can trigger signs and symptoms of schizophrenia, but only in individuals who are already predisposed to psychotic illness. In addition, these drugs increase heart rate, making it risky to give cannabinoids to patients with heart disorders such as angina. The transient psychotropic (i.e. 'mind-altering') effects of cannabinoids that constitute the 'high' are potentially dangerous to everyone who drives or operates machinery as these effects significantly reduce the ability to do so safely.
The clinical significance of reported effects of cannabinoids on levels of reproductive hormones in the blood and on foetal development in animals remains to be determined, but in the meantime, it would be unwise to take cannabinoids during pregnancy. It also remains to be established whether they can bring about irreversible changes in brain function of any importance. Another question still to be resolved is whether the suppressant effect of cannabinoids on the immune system presents a significant threat, particularly to AIDS patients who take cannabis or individual cannabinoids to obtain relief from nausea and loss of appetite.
Can cannabis only be smoked?
No, cannabis is also active when eaten. This is important as cannabis smoke may, like tobacco smoke, contribute to the development of lung cancer and chronic bronchitis. However, taking cannabinoids by mouth is not ideal as their rate of entry in the blood circulation is somewhat variable by this route. Consequently, other possible ways of giving these drugs to patients should be explored.
The need for more research
More clinical research is needed to investigate the validity of the claims made about the medical uses of cannabis and cannabinoids. In addition, the unwanted effects of cannabis must be more fully characterised. It will also be important to establish whether cannabis-related medicines should consist of a single cannabinoid, a combination of a few cannabinoids or a standard preparation derived from the whole cannabis plant. All this will take considerable time and there is strong case to be made for allowing doctors to prescribe cannabis now for named serious disorders, at least for a trial period.