IMPROVING THE QUALITY OF THE CANNABIS DEBATE: DEFINING THE DIFFERENT DOMAINS

The policy debate on cannabis has moved back into prominence in
Britain and elsewhere after reports of increases in use during the
early 1990s[1] and renewed claims about the therapeutic value of
marijuana.[2, 3] Rational debate has often been obstructed because the
media present a forced choice between two sets of views. One of these
constructed views is that cannabis is harmless when used
recreationally, is therapeutically useful, and hence should be
legalised. The other is that recreational use is harmful to health and
that cannabis should continue to be prohibited for recreational or
therapeutic purposes.[4]

This oversimplification of the cannabis debate has prevented a more
considered examination of eight conceptually separate issues (see
box). We believe that a competent consideration of these issues would
contribute to a more informed debate about the appropriate public
policies that could be adopted towards cannabis use for recreational
or therapeutic purposes.

Summary points

Cannabis use is increasing steadily in many countries and is most
prevalent among young people

The value of the debate on cannabis is seriously diminished by heated
contributions that obstruct rational consideration of important public
health and policy issues

The different domains of the debate should be considered in isolation
at first to allow a more objective analysis of the evidence

Substantial public investment in research into the different areas is
a prerequisite of rational consideration of public policies

Is cannabis a single product?

More than 60 different cannabinoids and over 400 active components
have been identified in samples of cannabis.[2] However, our interest
and concerns about associated harms could be much more focused. Should
we be especially concerned about the use of new cannabis preparations
with higher concentrations of tetrahydrocannabinol? Does using
cannabis that has a higher tetrahydrocannabinol content result in a
higher intake of tetrahydrocannabinol or do smokers consciously or
subconsciously titrate the dose, as do cigarette smokers?[5] What are
the rates of dependence and adverse health effects in people who use
these more potent forms of cannabis? Tetrahydrocannabinol is the major
psychoactive component of cannabis and hence is a logical starting
point for search and study.

Uncertainty over harm

The physical harms of regular cannabis use over years and decades have
long been a subject of scientific uncertainty. Recent evidence on
damage (to the respiratory tract, for example) is rekindling this
debate.[6-8] Now may be an appropriate time for renewed research
effort into the effects of long term cannabis use since sizeable
cohorts of long term users (20 years of use) are now available for
study. There is an important supplementary question for these studies,
given that tobacco smokers and alcohol consumers often use cannabis.
What is the interplay between the respiratory effects of long term
cannabis and tobacco smoking?

Cannabis and psychological harm

What is the nature of the relation between cannabis and psychosis and
other serious psychological harms? How strong is the evidence that
cannabis is causally implicated in the precipitation or exacerbation
of schizophrenia and other psychoses?[9,10] Three different clinical
conditions need specific consideration.

To what extent are there time limited, acute psychiatric disturbances
such as acute psychosis or panic attacks whose origins may lie in an
episode of cannabis use?[11,12]

To what extent might cannabis be implicated causally in the genesis of
long term psychiatric disorders that would not otherwise have
occurred?[13-15]

What weight should be attached to reports that cannabis use adversely
affects the course of established mental illnesses for example,
precipitating relapses of schizophrenia or manic depressive
illness?[15-18]

Dependence on long term cannabis use

How important and widespread is dependence on cannabis use? The
popular view is that cannabis is not a drug of dependence because it
does not have a clearly defined withdrawal syndrome. This is too
narrow a view of dependence. Substantial proportions of long term
cannabis users in non-treatment, community samples report that they
are dependent; many of them satisfy diagnostic criteria for dependence
according to the Diagnostic and Statistical Manual of Mental
Disorders, third edition, revised and ICD-10 (international
classification of diseases, 10th revision) as well as the severity of
depression scale[19,20] ; however, fewer consider that they have a
cannabis problem.[19] As many as one in 10 cannabis users have been
found to want to stop or cut down, find it very difficult to do so,
and continue to use cannabis despite the adverse effects that it has
on their lives.[21,22] How serious an impact this type of dependence
has on the lives of affected individuals and their families is
unknown, but enough cannabis users have sought treatment to warrant
the establishment of local programmes dedicated to
quitting.[23,24]

(BOX)

Domains of the cannabis debate:

* What is the importance of the different types of cannabis product
composition, presentation, and usage?

* What evidence is there of physical damage from long term
use?

* What evidence is there of psychological or psychiatric (acute and
chronic) consequences?

* How widespread is dependence on cannabis and how important is
this?

* Is cannabis a "gateway" drug and what is the importance of
this?

* Do some cannabinoids have therapeutic potential and how best can
this be used?

* To what extent, and in what ways, is fitness to drive compromised by
cannabis use, and for how long?

* What can we learn from experiences with cannabis control policies in
other countries?

(Credit: ANGELA SMITH)

(/BOX)

Is cannabis a "gateway drug"?

Reuter and MacCoun have examined seven very different ways in which
the concept of a gateway drug may be interpreted.[25] Cannabis is
typically the first illicit drug that is used by those who
subsequently develop problems with heroin and cocaine use.[26] Does
cannabis use play a causal role in this sequence of drug involvement?
That is the key question for policy, but a difficult one to answer
because adolescents who start using cannabis early and become heavy
users are found to be independently at higher risk of using other
drugs.[27] They are also more likely to keep company with peers who
are heavy drug users. If there were a gateway effect, would preventing
or delaying the onset of cannabis use (assuming that we could) prevent
flow on to other drug use or simply change the sequence of
involvement?

Overlooked therapeutic effects?

The cannabinoids are an overlooked group of therapeutic
drugs.[2,3,28-30] For over a decade there have been anecdotal and
clinical reports on the usefulness of cannabis preparations in
treating conditions like nausea, glaucoma, and multiple sclerosis.
What conclusions are possible on the evidence to date? What might be
learned from better investigation? What implications, if any, do these
therapeutic uses have for policies towards recreational cannabis use?
The accumulating body of evidence now indicates strongly at least some
hitherto uncharted therapeutic applications from some of the more than
60 different cannabinoids or other active products found in samples of
the herbal product.[2,28,29] However, it is almost certain that new
formulations of the relevant (as yet not clearly identified) active
components would be required in order to separate any therapeutic
effects from harmful effects from smoking the drug. Clinical trials to
explore possible therapeutic worth have recently been initiated.[30]
As with other medical challenges, disciplined search for active
therapeutic ingredients that address health problems which are
currently not well managed is now the way forward.[2,3,28,29]

Does cannabis interfere with driving?

To what extent does cannabis use interfere with skilled activities
such as driving a motor vehicle or operating machinery? The
recognition of the substantial morbidity and mortality caused by drink
driving has increased concern about a similar role for illicit drugs
in view of the increase in prevalence of use among young adults who
are most at risk of accidental injury.[1,31,32] Certainly, many
drivers stopped by the police or being treated for injuries have been
found to have blood or urine samples that test positive for
cannabis.[33,34] However, the importance of these positive
toxicological results and their implication for driving competence is
not entirely clear. In controlled studies, cannabis has been found to
produce impairment.31 This effect lasts well beyond perceived
intoxication, but the full effects seen in controlled research may not
occur to the same extent in "normal" driving on the road because of
compensatory responses by drivers who are aware of their impairment.
Furthermore, a clearer understanding will be required of the extent to
which a particular concentration of the drug (or its metabolites) can
reliably be taken as evidence that an individual's driving ability was
consequently impaired.[35] Additionally, given the widespread combined
use of alcohol and cannabis, it will also be important to establish
the effects on accident risk of combining alcohol and cannabis use.

Impact of national policy on cannabis use

What has been the impact of alternative cannabis control policies in
different countries on the prevalence of use? It has been difficult
confidently to assess the contribution made by different policies.
Nevertheless, opportunities do exist for retrospective, or
occasionally prospective, studies of the impact of changes in cannabis
laws or regulations in individual countries or states. In these
studies, adjacent and similar regions are used as quasi-controls to
assess the extent to which any observed changes in cannabis use result
from the regulatory or legislative change or merely reflect broader
trends in society. Careful, objective scrutiny of the available data
is only rarely evident.[36-39] This is hampered by secular increases
in cannabis use, the lack of large scale survey data in countries
which have and have not changed their cannabis policies, and the lack
of research on the effects of the law as it is applied rather than as
expressed in statute.

Rational consideration needed

A more rational consideration of public policies towards cannabis use
by adolescents and young adults is urgently required. This is
particularly important in view of the evidence of a major increase in
cannabis use over the past few decades,[1,40] the persistence of this
substantial level of use, and the continued major law enforcement
effort to apprehend cannabis users.[41] Furthermore, doctors need a
clearer understanding of the associated adverse health and
psychological consequences of acute and chronic use so that they are
better able to give appropriate advice to their patients.[42]
Substantial public investment in research will be needed to advance
our knowledge of the areas outlined above. In its absence, public
policy will continue to be made with premature foreclosure of debate
in the face of uncertainty by using arbitrary rules about which side
in the debate bears the burden of proof - those who defend the status
quo or those who wish to reform our cannabis laws. With research, and
with greater clarity in each of these domains, we will at last be in a
position to formulate evidence based public policy about cannabis. At
the end of the day, the final decisions will, as always, be the
outcomes of a political process, but the quality of these decisions
would undoubtedly be improved by the availability of better evidence
on each of the domains defined above.

Footnotes

Competing interests: A research grant from a private charitable
foundation provided part time employment support for JW while he
gathered the available scientific evidence for objective Cochrane-like
review. No control over the content of the review is exercised by the
fund or any other outside party.

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(Accepted 23 August 1999)