Short answer
There is no established dose of medical cannabis for glaucoma. No health agency publishes a milligram target. The barrier is timing. Smoked or vaporized cannabis lowers intraocular pressure (IOP) for about 3 to 4 hours. A patient would need 6 to 8 doses in 24 hours to match one daily eye drop. Ophthalmology groups, including the American Academy of Ophthalmology, do not recommend cannabis for glaucoma.
cannabis and eye pressure research studies
What the studies measured
Hepler and Frank reported in 1971 that smoked marijuana lowered IOP in healthy adults. Later work tested THC by inhalation and by mouth. Peak IOP reduction ran about 25 percent to 30 percent. The effect faded within 3 to 4 hours.
- Smoking and vaporization act in 30 to 60 minutes.
- Oral THC absorption is slow. Onset is 1 to 3 hours. Bioavailability is low, often under 20 percent.
- Topical cannabis drops do not work. THC is not water soluble, and no eye drop form is approved.
Dose figures in the literature
Doses in published trials ranged from about 5 mg to 20 mg THC by inhalation, and 20 mg or more by mouth. Those numbers came from small studies with few patients. They measured eye pressure for hours, not years. No trial has shown that cannabis prevents optic nerve damage or vision loss.
Cannabis Eye Drops for Glaucoma: Legal States Explained
Why dosing is the barrier
Standard glaucoma drops lower IOP for 12 to 24 hours. Latanoprost is one drop at night. Timolol is one drop twice a day. Cannabis needs repeated dosing to hold the same pressure range. Each dose also carries side effects: fast heart rate, low blood pressure, dizziness, and reduced alertness. These risks rise in adults over 60, the age group with the highest glaucoma rates.
cannabis and eye pressure research studies
Convenience as the deciding factor
Treatment adherence tracks with dose burden. One nightly drop is easier to sustain than 6 to 8 inhalations spread across a day. A patient who cannot keep that schedule gets pressure spikes between doses. Convenience here is not a preference. It decides whether the pressure stays controlled.
Questions to ask a clinician
- What is my current IOP, and what is my target?
- Which approved drop or procedure fits my eye?
- If I use cannabis, how does it interact with my drops?
- Can we track IOP across a full day, not one visit?
Federal law still classifies cannabis as Schedule I. The FDA has not approved any cannabis product for glaucoma.