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In the 1970s, glaucoma became one of the first medical conditions to be cited as justification for a compassionate exception to prevailing laws against cannabis use, and the United States government has been passing out joints to glaucoma patients for more than three decades. Cannabis as a treatment for glaucoma was first suggested in 1971 in a study that noted that smoking cannabis lowered Intraocular pressure (IOP) BY 25 TO 30 percent. 

Glaucoma is one of the medical conditions most commonly cited as being effectively treated by medical cannabis, and the actress and talk-show host Whoopi Goldberg (who suffers from glaucoma) always has her vaporizer with her in case she needs to medicate.

In the 1970s, researchers tried (and failed) to produce eye drops containing THC. They were unable to do so because the cannabinoids are not soluble in water. For this reason, cannabis is infrequently recommended by ophthalmologists for glaucoma treatment, but it remains one of the most common treatments for the disease.

Glaucoma is a catchall term used to describe a group of diseases that attack the optic nerve and is the leading cause of blindness. High pressure of fluid within the eye typically causes nerve damage. Primary open-angle glaucoma, the most common form, has no noteworthy signs or symptoms except the gradual loss of vision. Pressure builds up and damages the eye because the fluid within the eye (called aqueous humor) does not properly move from behind the iris into a small chamber at thge4 front of the eye, where it filters through a spongy tissue before passing into a larger channel and into the bloodstream.

Endocannabinoid receptors are located throughout the eye, including the retina, cornea, and surrounding tissues. These receptors are also located within the trabecular meshwork, which drains the intraocular aqueous humor from the eye. Glaucoma causes a buildup of aqueous humor, which is thought to cause damage in the retinal nerve cells. As the endocannabinoid system within the nerve cells become well understood, additional targets for cannabinoid medicines emerge. THC reduces IOP in glaucoma. CBD does not reduce pressure but offers neuroprotective benefits that likely protect retinal ganglia from injury from glaucoma.

Molecules to target glaucoma

THC is the key molecule related to relieving intraocular pressure, but high CBD cannabis is recommended for its neuroprotective effect on the optic nerve.  Consistent and lasting reduction in intraocular pressure is unlikely to be achieved by cannabis alone.

Dosing for glaucoma

THC has been shown to reduce intraocular pressure at doses of 5 milligrams, four times a day, though the ability of THC to reduce IOP may decline over treatment. The use of CBD or other cannabinoids to protect optic and retinal nerve tissue is still being studied. Innovative delivery methods to target the cannabinoid receptors within the eye are likely to be developed soon (in other countries, of course). These innovations rely on the use of “prodrugs,” pharmacologically inactive substances that the body metabolizes into drugs.

Methods of ingestion

Orally ingested THC is effective for short-term reduction of intraocular pressure due to glaucoma, but tolerance to the benefits of THC typically develops over time.

Vaporization is effective for short-term reduction of intraocular pressure (3 to 4 hours), but tolerance to THC’s effects builds following sustained usage, reducing its efficacy.

Although topical application to the eye in the form of eye drops would be the most beneficial form of administration, cannabinoid molecules are not well absorbed or distributed within the body and, therefore, not very effective. Eventually, researchers in another country might develop an innovative prodrug that the eye metabolizes into a cannabinoid that reduces pressure within the eye.