the good doctor on: Cannabis and Glaucoma
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
