Blog Vol.II, # 19. Cannabis and
Glaucoma
When I was back in the office
this week, I was reminded of the connection between cannabis and eye
pressures. I asked one of my patients
(as I do all my patients) if they smoke and their answer was: “only marijuana”. That got me thinking that I need to ask
patients directly if they are smoking or taking THC ( tetrahydrocannabinol)
because this has an effect on eye pressures and does alter the risk for
glaucoma.
The active ingredient in cannabis
will reduce the eye pressure when it is in high enough concentration. The problem with THC is that it is difficult
to tell what concentration is in the system, how the concentration affects each
individual, and how that dose affects the eye pressure. With alcohol
consumption, we know that a standard drink has 14 grams of alcohol (equal to 12
ounces of 5% beer or 5 ounces of 12% wine or 1 ½ ounces of 40% whiskey). We know the concentrations and have a good
idea about how that will affect a person. This is not so clear with THC.
I would like to point out that
THC is not a way to treat glaucoma if you have it or even if you are at risk
for it. In order to have a therapeutic
effect, enough THC to lower the eye pressure significantly, a person would have
to take anywhere from 18-20 mg of THC every 4 hours. The person would be
permanently sidelined under such circumstances, not to mention the high cost of
maintaining that concentration. Also of
note is that the pressure-lowering benefit is countered by the blood-pressure-lowering
effect of the drug. So THC’s effects on
eye pressure
gets cancelled out for the most part.
Further complicating factors are
that there are also inconsistencies with licensed vendors and their stated
concentrations and home grown or street purchased cannabis, then there are the
differences in individual responses to the drug. There are just way too many variables.
In the future I will ask about THC
use but it will have pertinence only if the drug has been taken within 3-4
hours of taking eye pressures during the eye exam as it will mess with the
results and could mask glaucoma which is a problem.
In summary, do not depend on THC use
to help with glaucoma, if possible, do not take it before your eye exam and be
forthright with your optometrist about usage, especially around eye exam time.
til next week,
The good doctor, Dr. Mark Germain, Burlington Eyecare
