Short answer: there is no reliable medical cannabis dosage for glaucoma. Smoked or vaporized cannabis can lower intraocular pressure, called IOP, for a few hours. But the drop is short, tolerance builds, and no study has shown that cannabis prevents vision loss from glaucoma. The American Academy of Ophthalmology and the American Glaucoma Society do not recommend it as a treatment.
What dosage research actually shows
Most human studies on cannabis and glaucoma are small and old. Researchers in the 1970s and 1980s gave people smoked cannabis or oral THC and measured eye pressure. The pressure fell in many participants. The effect showed up within an hour or two and faded by three to four hours. That timing is the problem. Glaucoma treatment works by keeping pressure low all day and night. A drug that leaves gaps overnight does not match that goal.
There is no standard dose. In studies, THC content, route, and timing varied. Smoked flower, vaporized oil, edibles, and tinctures do not deliver the same amount of drug. Even the same product can hit differently from person to person. Oral THC is especially unpredictable because absorption depends on food and metabolism. CBD is not a clean substitute either. Some research suggests CBD may raise IOP, which is the opposite of what you want.
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Tolerance matters too. With repeated use, the IOP-lowering effect gets weaker. A person may use more to get the same drop, which raises the risk of side effects. Those include dizziness, dry mouth, impaired coordination, memory problems, and respiratory irritation from smoke.
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Why eye doctors do not prescribe cannabis
Glaucoma care is built on steady control. Prescription drops, laser treatment, and surgery lower IOP with predictable timing. Cannabis does not fit that model. It also has not been shown to stop optic nerve damage or preserve vision in clinical trials. The positions from major eye groups are clear: marijuana is not a recommended glaucoma treatment. That does not mean cannabis is dangerous for everyone. It means the evidence does not support it as therapy for this condition.
If you have glaucoma, do not stop or change your prescribed drops to try cannabis. Talk with your ophthalmologist first. Keep your pressure checks on schedule. If you use cannabis for other reasons, tell your eye doctor. Bring the product label if you can. Legal dispensary products in the US should list THC and CBD content, but that label is not a dosing guide for glaucoma. I would not treat a dispensary label as a glaucoma dosing plan.
Bottom line
Medical cannabis for glaucoma dosage research has not produced a practical treatment. The window of pressure reduction is too short, tolerance is real, and vision protection is unproven. Standard glaucoma care remains the reliable path. If you are curious about cannabis for symptoms like anxiety or sleep, treat that as a separate question and keep your eye care team in the loop.