Is there a role for marijuana in medical practice?

Vol 52:  december • décembre 2006  Canadian Family Physician•Le Médecin de famille canadien 

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Debates

Is there a role for

marijuana in medical practice?

Mark A. Ware,

MB BS, MRCP(UK), MSC

C

rude preparations of herbal cannabis have been used for thousands of years to treat many symptoms, including pain, spasms, and nausea.¹ Preparations his- torically included extracts of roots, leaves, and flowering heads but were not commercially standardized or charac- terized. Modern pharmacology has identified the principal psychoactive ingredient of cannabis as delta-9-tetrahy- drocannabinol; specific cannabinoid receptors have been identified in the central and peripheral nervous system as well as in immune cells, endothelial tissue, and other vis- ceral organs.² Animal studies have confirmed that many of the effects of cannabis in humanbeings have solid neu- rophysiologic bases, particularly with respect to pain con- trol.³ The cannabinoid system is, therefore, a major target for drug development.⁴

History of medical cannabis policy in Canada

In 1999 the Court of Appeal for Ontario ruled that it was unconstitutional to enforce the rule of law with respect to cannabis.⁵ Since 2001, the Marihuana Medical Access Regulations (MMAR) have made cannabis possession legal for authorized patients in Canada. Since July 2005 the streamlined MMAR application requires that physi- cians sign a form confirming the diagnosis, the symp- toms, the fact that prior treatments have been tried or considered, that the use of cannabis has been discussed, and that cannabis is not an approved drug.⁶

There are 2 main categories of complexes recognized under the MMAR: those requiring approval from fam- ily physicians and those requiring approval from both family physicians and specialists. For the second cat- egory, family physicians must discuss the case with a specialist; whose name and the date of consultation, but not signature, are required. Amending this process appears to have increased the number of applications.

As of September 2006, 1492 persons were authorized to possess medical marijuana and 917 physicians had sup- ported applications under this program.⁷

Herbal cannabis, cultivated by Prairie Plant Systems Inc under licence to Health Canada, is distributed to authorized patients for $5/g. This herbal canna- bis is cultivated under controlled conditions, is free of contaminants, and is irradiated to destroy patho- genic microorganisms. It is delivered as a milled herb

NO

Meldon Kahan,

MD, CCFP, FCFP

Anita Srivastava,

MD, CCFP, MSC

I

n its Marihuana Medical Access Regulations, Health Canada authorizes physicians to prescribe dried can- nabis, an unproven and potentially dangerous substance, under the guise of medical treatment. The program is intended to help patients with serious illnesses, such as HIV infection and cancer, but severe arthritis is also listed as an indication. Surveys confirm that chronic pain and arthritis are common reasons for medical cannabis use.¹ As analgesics, however, pharmaceutical cannabis products are weaker and less well tolerated than opi- oids.² While cannabis users testify to its therapeutic ben- efits, they also commonly report pleasant psychoactive effects that are easily confused with direct analgesia.

Safer alternatives available

The main active ingredient in marijuana is delta-9-tetra- hydrocannabinol (THC), but both an oral THC and a buc- cal spray of THC and cannabidiol are available and are far safer than smoking dried cannabis. Cannabis smoke contains many of the same carcinogens as tobacco, and case-control studies suggest that cannabis smokers are at increased risk for prostate cancer and for head and neck cancer.³ Cannabis smokers are also at increased risk for bronchitis.⁴ Even if cannabis were vaporized and inhaled rather than smoked, the rapid delivery of high THC doses increases the risk of psychomotor impair- ment and addiction.

Risks associated with use

While many people smoke cannabis occasionally with- out obvious harm, regular cannabis smoking can be dangerous. Cannabis use is a major risk factor for psy- chosis and schizophrenia,⁵ aggravates psychotic symp- toms,⁶ and might have long-term cognitive effects.⁷ Adolescents who smoke cannabis have higher rates of other substance use, school failure, criminal activity, and suicidal thoughts.⁸ Cannabis impairs driving abil- ity and so is a risk factor for motor vehicle accidents.⁹ In utero cannabis exposure is associated with attention deficit disorders, behavioural problems, and poor aca- demic performance in childhood.¹⁰

Health Canada states that“the average daily amount approved for over 90% of patients … is 5 grams or less per day (5 to 10 joints)”. Based on Health Canada’s YES

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  Canadian Family Physician•Le Médecin de famille canadien  Vol 52:  december • décembre 2006

calculations, 5 joints with 12.5% THC concentration will contain approximately 400 mg of THC, or 20 times the maximum daily dose of oral THC. A single oral 5-mg dose reaches a peak plasma THC level of 5 to 10 ng/mL within 2 to 4 hours, whereas a single joint reaches 200 to 300 ng/mL within 6 to 9 min- utes. This disparity puts patients at substantial risk for adverse effects, including dependence and psychomo- tor impairment. Even at therapeutic doses, symptoms of intoxication affected 40% of subjects in trials of the THC and cannabidiol buccal spray, and 8% to 24% in the trials of oral THC.

Legal complications

Physicians are relatively safe from legal sanctions in cases of adverse drug reactions as long as they have exercised due precaution. This standard, how- ever, will not protect physicians who prescribe an unapproved drug, such as marijuana. The Canadian Medical Protective Association waiver purportedly absolves physicians of legal responsibility for untow- ard events related to cannabis prescribing, but it can- not protect physicians from legal action brought by third-party victims.

Society pays

From a public health perspective, the Health Canada program is fundamentally unjust and harmful. The pro- gram diverts resources to an unproven substance of uncertain efficacy with abuse liability, contributing to the public’s perception of cannabis as a harmless recre- ational product with therapeutic benefits.

Forty-seven percent of 18- to 19-year-olds in Canada have smoked cannabis in the past year, and 5% of Canadians report at least 1 concern related to cannabis.

Six thousand patients were treated for cannabis depen- dence in Ontario in 2000, which likely represents a small fraction of those who need help. As one author stated,

“… the costs to society are continuing to mount from past neglect of this continuing health problem.”¹¹

If legislators wish to decriminalize cannabis posses- sion, they should do so without disguising it as medi- cal therapy. Smoked medical marijuana is unnecessary and unsafe, especially in the doses allowed by Health Canada, and it distracts physicians and the public from the widespread harm caused by cannabis use and dependence.

Meldon 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 phy- sician at St Joseph’s Health Centre and a clinical research- er at the Centre for Addiction and Mental Health.

with 10 mm particles and moisture content of 15%. The potency is standardized at 12% ± 2.0% delta-9-tetrahy- drocannabinol.⁸

Cannabis and family physicians

What do family physicians need to know about the MMAR? First, there is a legal means by which patients can obtain quality-controlled cannabis for medical use.

Second, physicians do not “prescribe” cannabis under this approach but instead support a patient’s applica- tion for authorization to possess the drug. This process reduces the risk of prosecution for patients whose can- nabis use is part of a therapeutic approach. Third, medi- cal cannabis use can be documented and monitored as part of standard care.

Prescribed cannabinoids offer an alternative to herbal cannabis and should be considered in all cases where cannabis is discussed. Inhaled cannabi- noids have the potential pharmacokinetic advantages of bypassing the first-pass effect of hepatic metabo- lism, of rapid onset of action, and of easy titration.

Risks include irritation of the upper airways, cognitive effects of central cannabinoid activity, and stimulation of reward mechanisms.

Considerations

Advocates for medical marijuana are often involved in political action to change policy. For every placard-car- rying marijuana activist, however, many more silent sufferers have turned to cannabis where all else has failed. These patients might be afraid to discuss canna- bis with their doctor and might not be aware that they have other legal and safe options. Physicians will for- mulate their own moral and scientific positions based on available evidence. Cannabis has not yet been for- mally evaluated in clinical trials, but safety and efficacy studies are under way and further studies should be designed and conducted. Without such trials it is pre- mature to consider prescribing cannabis, but based on what is known of a drug that has been around for thousands of years, based on the safety data generated from 2 generations of recreational users, and based on the mechanism of action of cannabinoids, it is rea- sonable for family physicians to become more famil- iar with cannabis. Its undignified position as a drug of abuse with no known medical value deserves to be reconsidered.

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 practis- ing pain physician. Dr Ware receives salary support from the Fonds de la recherche en santé Québec and holds grants from the Canadian Institutes of Health Research.

YES NO

Debates

Vol 52:  december • décembre 2006  Canadian Family Physician•Le Médecin de famille canadien 

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Correspondence to: Dr Meldon Kahan, Department of Family Medicine, St Joseph’s Health Centre, 30 The Queensway, Toronto, ON M6R 1B5; telephone 416 530- 6478; fax 416 530-6160; e-mail [email protected] references

1. Swift W, Gates P, Dillon P. Survey of Australians using cannabis for medical purposes.

Harm Reduct J 2005;2:18.

2. Campbell FA, Tramer MR, Carroll D, Reynolds DJ, Moore RA, McQuay HJ. Are canna- binoids an effective and safe treatment option in the management of pain? A quali- tative systematic review. BMJ 2001;323(7303):13-6.

3. 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.

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

5. 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.

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

7. Dafters RI, Hoshi R, Talbot AC. Contribution of cannabis and MDMA (“ecstasy”) to cognitive changes in long-term polydrug users. Psychopharmacology (Berl) 2004;173(3-4):405-10.

8. Fergusson DM, Horwood LJ, Swain-Campbell N. Cannabis use and psychosocial adjustment in adolescence and young adulthood. Addiction 2002;97(9):1123-35.

9. 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.

10. Goldschmidt L, Richardson GA, Cornelius MD, Day NL. Prenatal marijuana and alcohol exposure and academic achievement at age 10. Neurotoxicol Teratol 2004;26(4):521-32.

11. Dennis M, Babor TF, Roebuck MC, Donaldson J. Changing the focus: the case for recognizing and treating cannabis use disorders. Addiction 2002;97(Suppl 1):4-15.

NO Correspondence to: Dr Mark A. Ware, E19.145,

Montreal General Hospital, 1650 Cedar Ave, Montreal, QC H3G 1A4; telephone 514 934-8222; fax 514 934-8096;

e-mail [email protected] references

1. Mechoulam R. The pharmacohistory of Cannabis sativa. In: Mechoulam R, editor.

Cannabinoids as therapeutic agents. Boca Raton, Fla: CRC Press; 1986. p. 1-19.

2. Pertwee RG, Ross RA. Cannabinoid receptors and their ligands. Prostaglandins Leukot Essent Fatty Acids 2002;66(2-3):101-21.

3. Meng ID, Manning BH, Martin WJ, Fields HL. An analgesia circuit activated by can- nabinoids. Nature 1998;395:381-3.

4. Bernadette H. Cannabinoid therapeutics: high hopes for the future. Drug Discov Today 2005;10(7):459-62.

5. Court of Appeals for Ontario. R. v Parker. Toronto, Ont: Court of Appeals for Ontario;

2000. Available from: www.ontariocourts.on.ca/decisions/OntarioCourtsSearch_

VOpenFile.cfm?serverFilePath=d%3A%5Cusers%5Contario%20courts%5Cwww

%5Cdecisions%5C2000%5Cjuly%5Cparker%2Ehtm. Accessed 2006 February 1.

6. Marihuana Medical Access Regulations. (2001). Canada Gazette, Part II (reference July 4, 2001-SOR 2001-227). Available from: http://www.hc-sc.gc.ca/dhp-mps/alt_

formats/hecs-sesc/pdf/marihuana/ marihuana-reg_e.pdf). Accessed 2005 Oct 1.

7. Health Canada. Marihuana for Medical Purposes. Statistics (September 1, 2006).

Ottawa, Ont: Health Canada; 2005. Available from: www.hc-sc.gc.ca/dhp-mps/

marihuana/stat/2006/sept_e.html. Accessed 2006 Oct 28.

8. Health Canada. Health Canada’s marihuana supply. Ottawa, Ont: Health Canada;

2005. Available from: http://www.hc-sc.gc.ca/dhp-mps/marihuana/supply- approvis/index_e.html. Accessed 2005 Oct 1.

YES

...

kEY POINTS

•

There is solid scientific rationale for therapeutic use of cannabis.

•

Pharmaceutical cannabinoid preparations should always be considered.

•

Mechanisms exist in Canada for herbal cannabis to to be used legally.

•

Ongoing research and education regarding cannabis is needed.

kEY POINTS

•

Cannabis use has been associated with multiple medical problems, including bronchitis, psychosis, and cognitive impairment.

•

The dose of dried cannabis recommended by Health Canada far exceeds the recommended doses of approved products that contain THC and thereby puts patients at risk for dependence and psycho- motor impairment.

•

There is no good evidence for medical marijuana, and physicians might be liable for prescribing an unapproved and unproven product.

Debates

Alexis Thomson and Alexander Miles Manual of Surgery. Volume First: General Surgery. Sixth Edition (1921).

HENRY FROWDE AND HODDER & STOUGHTON

I t is now generally recognised that one of the most likely sources of wound infec- tion is the hands of the surgeon and his assistants. It is only by carefully studying to avoid all contact with infective matter that the hands can be kept surgically pure, and that this source of wound infection can be reduced to a minimum. The risk of infection from this source has further been greatly reduced by the systematic use of

rubber gloves by house-surgeons, dress-

ers, and nurses. The habitual use of gloves

has also been adopted by the great major-

ity of surgeons; the minority, who find they

are handicapped by wearing gloves as

a routine measure, are obliged to do so

when operating in infective cases or dress-

ing infected wounds, and in making rectal

and vaginal examinations.