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  • Dr Anne Malatt

Is marijuana good for glaucoma?

Updated: Apr 21

One of the many myths that surround the use of marijuana is that it is good for glaucoma.

This is based on studies from the 1970s that showed it caused a drop of pressure by 3-5 points, lasting for up to 3 hours.

Now let’s break this down.

Glaucoma is a disease of the optic nerves, in which the pressure of the fluid inside the eye is too high to allow free flow of blood and nutrients through the optic nerve. If the pressure is very high or if the high pressure is sustained for a long time, it can cause nerve fibre damage with loss of peripheral vision initially, and eventually complete loss of vision. Chronic glaucoma causes no symptoms at all until severe visual loss occurs.

If we find a level of pressure that is causing nerve damage (and this level is different for everyone and can sometimes be statistically ‘normal’), we need to reduce the pressure by at least 30% in a sustained 24 hours a day way, to reduce the risk of continuing nerve damage.

Marijuana reduces the pressure by 3-5 points for 3 hours. This pressure drop is minimal and short-lived, and even if it were enough, you would have to smoke and or ingest more marijuana every 3 hours, day and night, to sustain the mild drop in pressure.

Studies have actually been performed trialling this, but none of the trial participants were able to complete the study as they were unable to tolerate the side effects of the drug.

If you were to use marijuana every 3 hours as a drug, the negative effects on mood, mental clarity and (if smoked) lung health would be significant. You would not be able to drive, operate machinery or engage in many daily activities. In addition, the cost of using marijuana every three hours, every day, would be prohibitive for most people.

Alcohol also reduces eye pressures by a few points in the short term, but no-one is suggesting people have a drink every hour day and night to treat their glaucoma.

In addition, as well as lowering eye pressure, marijuana can lower blood pressure, which can also affect the flow of blood and nutrients to the optic nerve, and it is possible that smoking marijuana could be counterproductive and make glaucoma worse!

At this stage, no-one has developed a drop that can be administered locally and shown to be effective and so there is no safe, effective and well-tolerated way of administering marijuana, cannabis or THC in a practical way to treat glaucoma.

We have many great treatments for glaucoma, including eye drops, laser, stents and other types of surgery and all of these need to be administered by or under the supervision of an ophthalmologist. Glaucoma is not just a disease of high pressure in the eye, as some people have the same progressive optic nerve damage with pressures that never rise above ‘normal’, and the diagnosis and treatment can be delicate and complex.

It is vital that everyone over 40, and even younger if there is a family history of glaucoma, have an eye health check every year for this condition which causes no symptoms at all, until it causes irreversible blindness. Self-diagnosing and self-medicating is not an option here… trained professionals are available to support you… please use them!

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