At the beginning of this course,
we talked about different types of pain.
You'll recall that in our conversation about acute pain,
we made reference to a broken leg or waking up after surgery.
One of the most common ways of treating acute pain is by prescribing pain killers.
The type of painkiller prescribed depends on
the severity of pain reported by the patient.
For mild pain, we use simple analgesics like paracetamol.
Whereas for moderate pain,
we generally employ weak opioids.
For strong pain we prescribe strong opioids drugs such as Morphine,
Oxycodone or Fentanyl, either alone or in combination with NSAIDs.
Anti-inflammatory drugs like ibuprofen or in combination with simple analgesics.
Although these analgesics are effective,
they frequently cause side effects.
NSAID can irritate the stomach,
opioids can cause nausea and sedation.
This brings me to the question that I get very frequently.
I'm asked if medical cannabis can be effective in alleviating the acute pain.
The answer should be simple.
Right? Consider that hundreds of thousands of
surgical procedures are performed around the world every day.
Most patients report postoperative pain,
which is typically short lived generally lasting just a few days.
This is essentially an ongoing pain laboratory.
Conducting clinical trials on the effect of
any treatment including medical cannabis on acute pain,
should be both simple and inexpensive.
With this in mind,
the effectiveness of medical cannabis on acute pain should be known
fact with a high degree of precision and certainty.
Yet sadly, the reality is quite the contrary.
Evidence for the effectiveness of medical cannabis for acute pain is poor at best.
In preparation for this talk,
I entered the search words cannabis and postoperative pain in Medline.
The medical search engine for the National Library of Medicine.
Guess how many results came up?
11. Changing the search word cannabis to marijuana,
increased the number to 15.
To give you a sense of just how low that is,
the search terms morphine and postoperative pain,
yielded over 6,500 results.
Why is that?
What's the reason for the lack of medical information about medical cannabis?
I truly don't know given the enormous interest in medical cannabis.
What has been published thus far?
A small study was published in 1981,
in which four different doses of cannabinoid named levonantradol,
were injected in 36 patients with acute postoperative or posttraumatic pain.
Patients were observed for six hours after each injection.
Results showed, that all four injected doses were more
efficient in reducing pain than the placebo.
There are a few issues with the study including the small number of patients,
medications were administered only once,
and the fact that intramuscular injections are no longer
considered an acceptable way of treating postoperative pain.
This study can therefore be viewed as an attempt to provide a proof of concept,
suggesting that cannabinoids can be effective for acute postoperative pain.
In 2003, 12 years later,
a second study appeared.
This time five milligrams of THC,
the main psychoactive constituent of cannabis,
were given as oil capsules to 20 women who underwent hysterectomy.
This is a relatively large operation which can be quite painful.
20 other women received identical placebo capsules.
Full hour plaster six hours after administration,
and the women were entitled to a rescue analgesics if needed.
This incidentally is a common ethical practice in analgesics trials,
especially when a placebo is used,
so patients are not left untreated.
In contrast to the results of the previous trial,
this study did not find any advantage in favor of
the THC treatment relative to the placebo.
I don't consider these results as a disproof of concept because we cannot
say with any level of certainty that the only dose used in the study,
five milligram of oil THC was sufficient
to reduce the type and intensity of pain treated.
A higher dose for instance might have achieved the desired effect.
The third and regrettably last study of
this topic appeared in 2006 just over a decade ago.
The study was conducted in Germany and was better designed.
Each of the 30 participants received escalating all doses of five,
10 and 15 milligram of a cannabis extract called cannador.
In parallel, each patient could take rescue doses of morphine,
through a self operated pump.
In other words if in pain,
patients could push a button and self
administer a small bold use of morphine into the vein.
The number of self administered doses of morphine were
counted in a six hour period following each dose of cannador.
Although the study was prematurely terminated due to
incidence of serious adverse effects in one patient,
results showed that all patients on
the low dose of cannador needed rescue doses of morphine.
Only 50% receiving the middle dose pushed the rescue button.
Just 25% of the patients required morphine
during the six hours follow up period for the high cannador dose.
Although not a placebo controlled RCT,
this nicely designed study seems favorable to cannabis for acute postoperative pain.
If we return to real life cases,
a more recent retrospective study from Jamaica,
shows that recreational marijuana users experience
more severe postoperative pain and required higher morphine doses than did non-users.
At first glance, these isolated retrospective studies seems meaningless.
It certainly does not say a lot about the effectiveness of
medical cannabis in controlling acute postoperative pain.
But this type of information may actually raise questions about
the potential effects of long term exposure to cannabis on our pain systems,
on the way we respond to
subsequent painful stimuli and on our response to other analgesic interventions.
To summarize, there is some evidence in support of the concept
that medical cannabis may be effective for acute postoperative pain,
but that evidence is not very strong.
We are still eager to see at least one significant large scale multi-dose study,
which will not only approve or disapprove the concept,
but will determine if medical cannabis can be used effectively in postoperative setting.
Elon EisenbergProfessor of Neurology and Pain Medicine
