IS THERE A ROLE FOR MARIJUANA IN MEDICAL PRACTICE?

These rebuttals are responses from the authors who were asked to
discuss "Is there a role for marijuana in medical practice?" in the
Debates section of the December issue (Can Fam Physician
2006;52:1531-3 [Eng], 1535-7 [Fr]). In these rebuttals, the authors
refute their opponents' arguments.

YES

Mark A. Ware, MB BS, MRCP (UK), MSC

Drs Kahan and Srivastava assert that marijuana is prescribed "under
the guise of medical treatment" and object to "disguising it as
medical therapy." This refusal to accept that some patients use
cannabis as part of medical care runs contrary to current medical
opinion, including the Canadian Medical Association's position.1
Under the Marihuana Medical Access Regulations, cannabis is not prescribed.

Drs Kahan and Srivastava claim that cannabis use causes "pleasant
psychoactive effects that are easily confused with direct analgesia."
Cannabinoids have complex central actions, including analgesia. Are
pleasant side effects a valid reason to withhold the drug from
chronically ill patients?

They list a number of risks, many of which are controversial. The
carcinogenic potential of cannabis is not supported by clinical
evidence. Exposure to smoked cannabis (50 joint-years; equivalent to
1 joint daily for 50 years) is not independently associated with
increased risk of aerodigestive cancer; light cannabis use ((1
joint-year) might actually reduce risk of lung cancer.2 The
anticancer properties of cannabinoids are fascinating.3 Cognitive
effects of cannabis disappear after cessation of heavy use (50
joint-years).4 The risk for fatal accidents might actually be reduced
compared with controls following cannabis use.5 No evidence of abuse
of prescription cannabinoids has been found.6

Most cannabis research has been conducted under a paradigm of
prohibition, and the study of risks is not yet balanced by
much-needed research on benefits. All drugs have risks. To reject the
therapeutic potential of cannabis and cannabinoids on the grounds of
toxicity and potential abuse is to throw the baby out with the bath water.

Dr Ware is Assistant Professor in Anaesthesia and Family Medicine at
McGill University in Montreal, Que, Associate Medical Director of the
MUHC Pain Centre, and a practising pain physician. He receives salary
support from the Fonds de la recherche en sante Quebec and holds
grants from the Canadian Institutes of Health Research.

References

1. Canadian Medical Association Office for Public Health. Medicinal
use of marijuana. Ottawa, Ont: Canadian Medical Association.
Available from: www.cma.ca/index.cfm/ci_id/3396/la_id/1.htm. Accessed
2006 Nov 24.

2. Hashibe M, Morgenstern H, Cui Y, Tashkin DP, Zhang ZF, Cozen W, et
al. Marijuana use and the risk of lung and upper aerodigestive tract
cancers: results of a population-based case-control study. Cancer
Epidemiol Biomarkers Prev 2006;15(10):1829-34.

3. Guzman M. Cannabinoids: potential anticancer agents. Nat Rev
Cancer 2003;3(10):745-55.

4. Pope HG Jr, Gruber AJ, Hudson JI, Huestis MA, Yurgelun-Todd D.
Neuropsychological performance in long-term cannabis users. Arch Gen
Psychiatry 2001;58(10):909-15.

5. Bates MN, Blakely TA. Role of cannabis in motor vehicle crashes.
Epidemiol Rev 1999;21(2):222-32.

6. Calhoun SR, Galloway GP, Smith DE. Abuse potential of dronabinol.
J Psychoactive Drugs 1998;30(2):187-96.

NO

Meldon Kahan, MD, CCFP, FCFP Anita Srivastava, MD, CCFP, MSC

Dr Ware states that cannabis has been used for thousands of years.
Yet many time-honoured medical therapies are abandoned as it becomes
evident that they are harmful or as they are replaced by more
effective treatments. Dr Ware encourages family physicians to learn
about the Marihuana Medical Access Regulations because physicians do
not have to prescribe medical marijuana but simply to support its
legal use. The access form might not be an official prescription, but
patients will interpret the physician's signature as an endorsement
of the therapeutic benefits of smoked marijuana. Patients trust their
physicians and expect physicians to act in their best interests;
therefore physicians should sign the form only if they truly believe
that medical marijuana is safer or more effective than available
alternatives. This position is untenable now that oral and inhaled
pharmaceutical cannabinoids are available.

Dr Ware admits that, although "cannabis has not yet been formally
evaluated in clinical trials," family physicians should become more
familiar with it because studies are under way. Yet most clinical
trials are testing pharmaceutical cannabinoids, not smoked marijuana.
We are reassured that marijuana has "safety data generated from 2
generations of recreational users." This statement is unreferenced,
and we take issue with Dr Ware's commonly held view that cannabis is
a harmless herbal remedy. Its harms are well studied and documented;
marijuana smokers are likely at increased risk of prostate, head, and
neck cancers1; bronchitis2; motor vehicle accidents3; psychosis4,5;
and psychosocial difficulties. Marijuana smoke contains numerous
toxins, and the rapid delivery of high doses of inhaled
delta-9-tetrahydrocannabinol puts smokers at risk of psychomotor
impairment and addiction. It is inadvisable for family physicians to
prescribe an unproven and possibly harmful substance to their
patients when far safer alternatives are available.

Dr Kahan is Medical Director of the Addiction Medical Service at St
Joseph's Health Centre in Toronto, Ont, and Head of the Alcohol
Clinic at the Centre for Addiction and Mental Health. Dr Srivastava
is a staff family physician at St Joseph's Health Centre and Head of
the Opioid Clinic at the Centre for Addiction and Mental Health.

References

1. Hashibe M, Straif K, Tashkin DP, Morgenstern H, Greenland S, Zhang
ZF. Epidemiologic review of marijuana use and cancer risk. Alcohol
2005;35(3):265-75.

2. Tashkin DP, Baldwin GC, Sarafian T, Dubinett S, Roth MD.
Respiratory and immunologic consequences of marijuana smoking. J Clin
Pharmacol 2002;42(11):71-81.

3. Ramaekers JG, Berghaus G, van Laar M, Drummer OH. Dose related
risk of motor vehicle crashes after cannabis use. Drug Alcohol Depend
2004;73(2):109-19.

4. Green AI, Tohen MF, Hamer RM, Strakowski SM, Lieberman JA, Glick
I, et al. First episode schizophrenia-related psychosis and substance
use disorders: acute response to olanzapine and haloperidol.
Schizophr Res 2004;66(2-3):125-35.

5. Caspari D. Cannabis and schizophrenia: results of a follow-up
study. Eur Arch Psychiatry Clin Neurosci 1999;249(1):45-9.