Saturday, August 30, 2014

Reefer Madness part two

Medical marijuana has its boosters and detractors.  I have rarely seen a topic in medicine so polarized.

The following points have been raised by one side or the other.

From the medical establishment.

There is no evidence of the efficacy of medical marijuana

Actually there is considerable evidence of the efficicacy of cannabinoids in both pain and spasm both in human and animal studies.  Cannabinoids have in fact been thoroughly studied, possibly more than many classes of drugs.  The mechanism of action is quite well understood.  There has only been one study comparing smoked marijuana with placebo but this is a reflection of the difficulty of studying a drug which is illegal in most of the world.  This study was by the way positive in favour of smoked marijuana.  

The percived lack of evidence is more of a sad reflection on the academic pain community and the pharmaceutical industry who have had 13 years to test marijuana for pain but have with a few exceptions sat around twiddling their thumbs or pontificating.

Further if we look critically at the evidence for many conventional treatments they too are quite weak.  Even the best treatments for pain have a NNT of 3 or higher which simplistically means that they don't work in over 2/3 of patients.  Then we have to look at the large number of drugs that are used off label for which no studies have been done, the drugs that are used in pediatric patients and the drugs that are used in the frail elderly; neither children or frail elderly get included in clinical trials.  And of course we have to look at the treatments which have never been tested because, well, we've always done it that way.

The potency of medical marijuana is variable and unpredictable.

This would almost be a valid argument if conventional drugs had pharmacokinetics and dynamics which were constant from person to person.  But we all know that isn't true.  If we for example give 10 mg of morphine IV to a group of similar 70 kg individuals we know that we can expect a variety of responses.  Some people will get sleepy, some nauseated, some itchy.  Some will get good analgesia, some will get no analgesia.  This applies to most drugs which is why when things are critical we measure blood levels as we do with antibiotics, digoxin and many anticonvulsants.  Further as we all know and practise in anaesthesia, we titrate to effect.  

This also assumes that bioavailable is constant for the same drug.  We also know this isn't true, there are huge differences in bioavailability between generic and brand name drugs.  This is of course a major problem with drugs like Coumadin and Digoxin.  

The current requirement to obtain drug from a registered supplier also means that patients can get marijuana of known potency.  Not that I like to praise any policy derived by our Canadian Tea Party.

Smoking is harmful

Hard to argue with this one.  Except.

As every anaesthesiologist knows one of the best ways to deliver drugs is through the lungs.  A lot more drugs would probably be administered by this route if a reliable delivery system could be devised.    Smoking while harmful does deliver vapour to the lungs.

It is also possible to purchase a vapourizer to vapourize the marijuana.  This may or may not be safer than smoking.

Patients who smoke marijuana for pain typically smoke way less than do recreational users.  Many patients will only take one or two puffs and typically less than 2 grams a day are necessary.  Interestingly enough our government allows patients to have up to 5 grams a day.

It is possible to take marijuana by the oral route as well.  Because of the reduced bioavailability higher doses are necessary which can be a problem with a drug which is controlled tightly and now fairly expensive.  There is an interesting book, "Cooking with Cannabis" available for free download on the internet.

We have many good treatments for pain, marijuana should not be necessary

Except we don't.  Most of the drugs we have either don't work or are not tolerated in large proportions of patients (this also applies by the way to marijuana).  Some like opioids are extremely controversial.  Multi-disciplinary pain clinics have long wait lists, are expensive and quite frankly really aren't that efficacious.  (At a seminar I gave to a group of pain physicians years ago, I asked if anybody had ever seen somebody benefit from a rehab program.  Only one person had.)  Interventional treatments are great for the interventionalist's bank account but are of limited benefit for patients.  

Further marijuana or any treatment should not be a stand alone treatment but should ideally be a part of an inter-disciplinary approach to pain involving many modalites, focused on the patient.  I also believe in the Easter Bunny.

Marijuana can cause psychosis.

This is based on a retrospective observational study looking at the developement of schizophrenia in teenagers using marijuana.  Funny how observational studies are okay when they justify somebody's agenda.  The saying correlation does not imply causation applies here, and it is quite likely that teenagers with the early symptoms of schizophrenia might be tempted to try marijuana, easily available in most high schools to relieve these symptoms.  Notwithstanding this, I will not authorize it for teenagers (easy for me because I only see adults).  

Conventional drugs are not innocuous either.  NSAIDs cause GI bleeding and renal failure with prolonged use.  Acetaminophen cause liver and kidney disease.  Anti-depressants cause weight gain.  Opioids cause endocrine abnormalities and have been shown to produce loss of grey matter.  I could go on.  

Cannabinoids may be effective but we should wait until more research is done and until the pharmaceutical industry comes up with a pharmaceutical product.

Again, how much more research do we need?  Marijuana has been sort of legal in Canada for medical uses since 2001 and have we seen any new products?  (Oh I forgot, we don't do pharmaceutical research in Canada.)    The only recent cannabis derived product to come out is Sativex which was developed in Britain.  Some pharmaceuticals may have something in the pipe as it were.   While most of Big Pharma is inherently evil, most of use would welcome the opportunity to be able to prescribe something made by Pfizer or Eli Lilly.

Doctors are being forced......

No they are not.  If they chose to write a prescription, they can if they don't they can refuse, just like they can refuse any service which is not life or limb threatening.  This applies by the way to other requests that may be made by patients.  It is the failure of physicians to act as responsible gatekeepers which helps to maintain the ongoing crisis in healthcare.

And from the advocates of medical marijuana:

Marijuana is a natural medicine.

Actually the marijuana smoked today bears very little resemblance to that smoked 100 or even 30 years ago.  Todays marijuana is the product of breeding and cloning to maximize the amount of THC.  It is for the most part grown hydroponically using who knows how many chemicals.  If you want to consider that natural, go ahead.

Marijuana was widely used as a medicine prior to being made illegal.

Not really a great endorsement.  Strychnine, arsenic and mercury were also widely used as medicines.  Marijuana based preparations were used in the 19th and early 20th century.  They didn't persist largely because they didn't work that well.  Further they were not used in Western medicine prior to their introduction from India in the mid 19th century. 

Marijuana is a wonder drug, a panacea

When I used to give talks on chronic pain management, the first thing I would tell the audience is that there are no panaceas.  This applies to marijuana.

In closing

We don't have a lot of good treatments for chronic pain and most of us in the business welcome any addition to our tool box.  Most of us don't like the way medical marijuana came about, by a court decision, we would rather the government had shown some leadership there.  We are stuck with a bad process and those of us who have chosen to authorize or prescribe are trying to do what is best for our patients.  

It would certainly be refreshing to get a dialogue free of hyperbole because this is not going away.

3 comments:

Anonymous said...

Cannabinoid studies should not be confused with medical marijuana (smoking the whole leaf). How many medications do we smoke? Think about it; If the lungs were the best method then why not nebulize like albuterol. Also, why include all the other non-useful components of the leaf...we don't do that with opium poppy or any other drug for that matter. Further, oral cannabinoids exist as treatment (e.g. Marinol).

So, if you want to promote the use of cannabinoids than more power to you. But you should focus on the pharmacologic properties and appropriate delivery of the drug, like we do with every other drug.

DONELLA FLORENCE said...

I just have to say Great information. I like how you have presented your information in outstanding detail. Thanks for sharing it !

Australian Medical Council books

Arthur Andreas said...
This comment has been removed by the author.