DOES MARIJUANA REALLY RELIEVE PAIN?

The use of marijuana for a few carefully selected medical conditions
has generated heated discussion, pitting those who favour
legalization against those who warn about the undesired consequences
of wider availability. Absent from much of the debate so far,
however, is scientific evidence to establish whether marijuana really
works to relieve chronic pain; and if it does, whether it does so in
a manner that is distinct from simply providing the well-known high
that has made it a popular recreational but illicit drug. This
edition of Health-Watch takes a closer look at the burden of chronic
pain and a recent study that has received a great deal of attention.

What is neuropathic pain?

For the sake of differentiation, let's take a look at two main types
of pain: non-neuropathic and neuropathic. Non-neuropathic pain is
more common and is caused by such things as bumps, bruises, sprains,
fractures and inflammation caused by arthritis.

Neuropathic pain, on the other hand, is the result of injury or
abnormal signals coming from the peripheral nervous system - that is,
the nerves outside of the brain or spinal cord. Neuropathic pain can
occur as the result of such conditions as shingles, cancer, phantom
limb pain, the phenomenon known as entrapment neuropathy - in which a
nerve is pinched ( as occurs in carpal tunnel or chronic back pain
syndromes) - and peripheral neuropathy, which is common among diabetics.

The symptoms of neuropathic pain include a constant gnawing pain, as
well as a shooting and burning sensation, or tingling and numbness.
No matter how you describe it, its effects can be debilitating,
causing tremendous physical and emotional suffering and loss of
quality of life. Not surprisingly, patients who suffer from
neuropathic pain experience high rates of depression and insomnia.
Neuropathic pain is frequently chronic, sometimes lasting months or
even years. While complete cures are unlikely, it can be controlled
with the proper treatment.

How might THC work?

The substance known as tetrahydrocannabinol ( or THC), which was the
subject of the study we are looking at, belongs to the family of
compounds known as cannabinoids, which are closely related to
pain-relieving molecules released by our own bodies. THC is the
cannabinoid extracted from the Cannabis sativa ( hemp) plant commonly
known as marijuana, or pot.

The medical use of cannabis or marijuana is not new. Cannabis sativa
has been used to treat pain since the third millennium BC. Between 10
and 15 per cent of patients with chronic pain caused by a variety of
conditions, including multiple sclerosis, currently smoke cannabis
for its seemingly helpful effects.

The study

Ware MA, Wang T, Shapiro S, et al. Smoked cannabis for chronic
neuropathic pain: a randomized controlled trial. CMAJ, August 30,
2010. DOI: 10.1503/ cmaj. 091414.

What was unique and important about this study?

Investigators at McGill University undertook a remarkable challenge
in conducting this study. In addition to dealing with the enormous
regulatory hurdles to performing research on cannabis, the team
needed to develop a true placebo, or pretend cannabis, that would be
indistinguishable from the real McCoy to determine the exact effects
of the THC without a psychological effect. The study tested four
potencies ranging from the zero per cent placebo dose to a 10 per
cent THC concentration. The researchers managed to recruit 23
neuropathic pain patients who were suffering from pain arising from
an earlier injury or a surgical procedure. They were randomly
assigned to the four dosing regimens and took a single inhalation of
the smokable capsules provided to them containing the active
ingredient or placebo, three times a day for two separate five-day periods.

Of key interest to the researchers was whether there would be a
reduction in the severity of the pain that the subjects experienced.
However, the researchers also measured other parameters: levels of
anxiety, depression and the ability to sleep restfully. The
investigators also wanted to know whether subjects experienced a high
from the test drug.

What did the study show?

The highest potency of THC reduced the level of pain by a modest
amount, while the weaker preparations had only marginal effects. In
addition, the higher levels of THC improved the subjects' ability to
fall asleep and led them to report a more restful night. There was no
apparent effect on overall mood, nor any evidence of this small
exposure to cannabis leading to a perceived high.

What does this mean for those suffering from neuropathic pain?

While the McGill study is a welcome addition to what is a fairly
sparse number of well-done studies, there is still more to learn
about how to make cannabis as acceptable and as safe as possible. In
the meantime, a patient's autonomy in making the best decision for
his or her particular circumstance should be paramount, and this
study provides some guidance in that regard.

How can patients obtain THC legally?

Synthetic cannabinoids are sold in Canada in pill form as Marinol and
Cesamet. While in most countries it is illegal to smoke cannabis for
recreational use, as a medicine it is legal in Canada, Germany, the
Netherlands, Spain and Israel, among other countries. To legally
smoke marijuana, one has to find a doctor willing to sign a
prescription for the drug. Health Canada then approves the possession
licence, and the prescription is filled by growing a small supply of
marijuana or by buying it from Health Canada. The organization
estimates that approximately 4,000 Canadians have been granted a
licence to possess marijuana legally. The material provided in
Health-Watch is designed for general educational purposes only and
does not pertain to individual cases. It should not replace necessary
medical consultations with your own doctor or medical professional.