CBD for glaucoma

There is no evidence that CBD helps glaucoma, and some evidence it could make eye pressure worse. In the only human trial, CBD did not lower eye pressure, and a 40 mg dose raised it for a few hours. Animal studies point the same way.

Glaucoma is a group of eye diseases that damage the optic nerve, often linked to high pressure inside the eye (intraocular pressure). Lowering that pressure is the main aim of treatment.

What the research shows

The only human trial (Tomida 2006)

Researchers in the UK gave six people with raised eye pressure or early open-angle glaucoma four single doses under the tongue, on separate days and in random order: 5 mg of THC, 20 mg of CBD, 40 mg of CBD, and a placebo.¹

The authors concluded that 20 mg of CBD “did not reduce IOP, whereas 40 mg CBD produced a transient increase IOP rise”.¹ (IOP stands for intraocular pressure.) With only six people and single doses, this is a pilot study, but it is the only human evidence there is for CBD and eye pressure.

Animal studies

• In a 2018 study in mice, THC eye drops lowered eye pressure by about 28% for eight hours. CBD, “contrary to expectation”, had two opposing effects on eye pressure and stopped THC from lowering it.²
• The American Academy of Ophthalmology (AAO), reporting on this research from Indiana, said the CBD eye drops raised eye pressure in the animals by 18% for at least four hours.³
• Results for experimental CBD eye-drop formulations are mixed. One 2022 study reported that a specially designed CBD eye drop lowered eye pressure in rabbits with normal eye pressure.⁴ None has been tested for glaucoma in people.

Animal results do not always carry over to people. Here, though, the animal and human findings agree: neither shows CBD lowering eye pressure.

Where the cannabis and glaucoma idea comes from

The idea that cannabis lowers eye pressure dates to 1971, when smoking cannabis was found to reduce it.⁵ That effect comes from THC, not CBD.¹² Even for THC, the effect is short. An Australian ophthalmologist, writing in 2021 in an article republished by Glaucoma Australia, said that cannabis’s role as a glaucoma treatment is limited by a short duration of action, mind-altering effects and the possibility that the effect fades with repeated use. The same article noted that CBD partly counteracts THC’s pressure-lowering effect.⁵ A US National Academies review concluded there is “limited evidence that cannabinoids are an effective treatment for improving intraocular pressure”.⁶

See CBD vs THC.

What doses were tested

The human trial used single doses of 20 mg and 40 mg of CBD under the tongue.¹ The higher dose is the one that raised eye pressure. Both are below the Australian limit of 150 mg a day for pharmacist-only (Schedule 3) CBD,⁷ so the rise was seen at a dose many products could supply. No longer-term or higher-dose study of CBD in glaucoma exists.

What Australian medical bodies say

• Glaucoma Australia. An article published by the patient organisation in 2017 said cannabis can lower eye pressure only temporarily, that in most cases “therapeutic benefit did not outweigh toxicity” for oral THC, and quoted the National Academies’ finding of limited evidence. It did not discuss CBD.⁶
• RACGP. The Royal Australian College of General Practitioners says medicinal cannabis should only be considered after first-line, evidence-based treatments have been exhausted.⁸
• TGA. The Therapeutic Goods Administration’s guidance says medicinal cannabis should be considered only when registered medicines have been tried, and stopped if benefit is not shown.⁹

We found no position statement on cannabis from the Royal Australian and New Zealand College of Ophthalmologists. Overseas, the AAO says that it and the American Glaucoma Society do not support using marijuana for glaucoma, because eye pressure needs control around the clock, and that ophthalmologists recommend patients stick with their prescribed therapy.³

Risks to know about

• Higher eye pressure. The 40 mg result in the human trial and the animal findings are the main concern for people with glaucoma.¹³
• Stopping proven treatment. Glaucoma damage cannot be reversed. The AAO notes that eye pressure needs to be controlled 24 hours a day.³ Replacing eye drops with an unproven product risks losing sight.
• Older adults and other medicines. Glaucoma is more common with age, and many older people take several medicines. CBD affects liver enzymes that process many drugs and can cause sleepiness.¹⁰ See CBD for older adults and CBD drug interactions.
• THC products. Cannabis products with THC cause intoxication and affect driving. The TGA says patients should be advised they are not able to drive while being treated with medicinal cannabis.⁹ See CBD and driving.

If you are considering it

• Talk to your optometrist or ophthalmologist before using any CBD or cannabis product, and do not stop your eye drops.
• Ask whether your pressure is well controlled on current treatment and what the other options are if it is not.
• If you already take CBD for another reason, tell your eye specialist so your eye pressure can be checked.

See talking to your GP about CBD.

This page is general information, not medical or legal advice. Laws and evidence change; we show the date we last checked the facts at the top of every page. Talk to your doctor or pharmacist before starting, stopping or changing any medicine.

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