Pubdate: Fri, 18 Apr 2014
Source: Montreal Gazette (CN QU)
Copyright: 2014 Postmedia Network Inc.
Contact:  http://www.montrealgazette.com/
Details: http://www.mapinc.org/media/274
Author: Christopher Labos
Note: Christopher Labos is a cardiologist practising in Montreal.
Page: A17
Bookmark: http://www.mapinc.org/mmjcn.htm (Cannabis - Medicinal - Canada)

IS MEDICAL MARIJUANA EFFECTIVE?

The Evidence Shows That Enthusiasm for Medical Marijuana Has Outpaced 
the Scientific Evidence in Favour of It

With very little fanfare, Health Canada has changed the law and now 
allows physicians to prescribe marijuana to patients for certain 
medical conditions. On April 1, Health Canada implemented its 
Marihuana for Medical Purposes Regulations.

Why it chose April Fool's Day and why it spells marijuana with an "h" 
are still unclear to me. Nevertheless, Canadians can now go to their 
doctor and ask for a prescription of dried cannabis for medical 
purposes. But just because you can does not mean that you should.

Of the many purported health benefits of marijuana, the most-often 
repeated is its ability to prevent glaucoma. Unfortunately, the 
evidence to support that claim is fairly limited. First, there are no 
major trials on the subject; and most of the evidence is from small 
studies of only a handful of patients.

Glaucoma is caused by high pressure within the eye, and these studies 
show that delta-9-tetrahydrocannabinol (THC, the active ingredient in 
marijuana) has some ability to lower intra-ocular pressure. However, 
this dip in pressure lasts only a few hours. Whether it has longterm 
benefits is unknown. Also, it appears to be very dose-dependent. 
Whereas 5 mg showed a temporary decrease in pressure, the 20-mg dose 
showed no effect, and the 40-mg dose actually increased pressure in the eye.

As a result, the Canadian Ophthalmological Society does not support 
the use of marijuana to treat, or prevent, glaucoma, citing its short 
duration of action, its psychotropic side effects and the fact that 
much better treatments for glaucoma already exist - namely a variety 
of eye drops and laser surgery.

The other main claim to fame for marijuana is its use to prevent 
chemotherapy-induced nausea and vomiting (CINV).

Synthetic cannabinoids like nabilone and dronabinol have been 
available and in use for some time. Although they have some 
antiemetic effect and are superior to a placebo sugar pill, there is 
no clear evidence that they are better than other medications to treat nausea.

Bear in mind that most of the evidence relates to these medications 
in pill form, not to the smoking of marijuana, for which little data exist.

So while there might be some role for cannabinoids when first-line 
medications like ondansetron are ineffective, their role is fairly limited.

The benefit of marijuana to aide in musculoskeletal pain and other 
neurological syndromes is also somewhat dubious.

There have been a few studies in patients with multiple sclerosis. A 
Canadian study published in the Canadian Medical Association Journal 
in 2012 suggested a benefit to patient-reported symptoms, but not in 
the objective timed-walk test.

However, this study was unblinded and therefore prone to bias from 
the placebo effect. Two studies of note, the CAMS and the CUPID 
study, both published in the Lancet in 2003 and 2013 respectively, 
showed no benefit to using THC.

Studies in diseases like Huntington's disease and Tourette's syndrome 
have also shown no benefit. The data for epilepsy are conflicting, 
with some studies suggesting a benefit while other studies suggest an 
increased epilepsy risk. There are no studies on fibromyalgia or 
arthritis. A recent review by Dr. Mary-Ann Fitzcharles of the McGill 
University Health Centre concluded there was no benefit to marijuana 
in most rheumatological conditions.

Unfortunately, the enthusiasm for medical marijuana has outpaced the science.

Although there might be some role for it, specifically in cancer 
patients, the evidence is hardly overwhelming. Also, almost all the 
studies I have mentioned here look at THC in pill form, not in 
smoking a marijuana cigarette.

Although likely far safer than nicotine cigarettes, smoked marijuana 
may still have some association with lung disease and cancer. So 
while smoking marijuana is not nearly as dangerous as heroine or 
cocaine, and while an argument can be made for its decriminalization, 
its medical use is very limited.

So to all those proponents and enthusiasts of cannabis, I suggest you 
write to your member of Parliament and make your case. Leave your 
family doctor alone. He or she is busy enough as it is.
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MAP posted-by: Jay Bergstrom