Can Cannabis Help Glaucoma Patients?

In 1976, a glaucoma patient named Robert Randall became the first person in the US to be granted legal status as a medical marijuana patient. As a teenager, Randall had been diagnosed with glaucoma and was told by doctors he would likely lose his eyesight before his 30th birthday. After learning of research that indicated THC could be an effective treatment for the disease, he began smoking marijuana. He was subsequently arrested for marijuana cultivation in Washington, D.C., but wasn’t convicted of the charges based on a defense of medical necessity. Thus, the cannabis and glaucoma debate began.

Randall then petitioned the Food and Drug Administration to provide marijuana to treat his disease. In 1976 the FDA approved the petition, later launching the Compassionate Investigational New Drug (IND) program to provide unapproved but promising drugs including cannabis to Randall and patients like him. After receiving shipments of joints from the federal government for 25 years to treat the disease, Randal died at the age of 53 in 2001. During that time, he never lost his eyesight.

What is Glaucoma?

Glaucoma is a group of related diseases of the eyes characterized by a buildup of fluid in the eye resulting in an increase in interocular pressure (IOP). The condition causes pressure on the optic nerve leading from the eye to the brain, leading to a slow loss of vision that can culminate in blindness. Traditional treatments for glaucoma include eye drops, oral medications and surgery. Glaucoma is the leading cause of blindness among people older than 60, according to the Mayo Clinic.

Some research has shown that THC, the cannabinoid largely associated with the classic marijuana “high,” can temporarily reduce IOP, thereby reducing the pressure on the optic nerve. A review of research into cannabis and glaucoma published in 2019 found that five randomized clinical trials found evidence that cannabis could lower interocular pressure. However, the researchers noted that the studies reviewed had design flaws including a small sample size and inadequate controls. But the glaucoma and marijuana studies also failed to compare the effects of cannabis on glaucoma to traditional treatments. The study concluded that randomized clinical trials (RCTs) showing the efficacy of cannabis as a treatment for the disease were necessary before its use could be recommended.

“The studies that were reviewed were highly variable in their methods and patient population selected, and therefore no current evidence supports the use of any form of cannabis to replace existing,” the authors of the review wrote in their conclusion. “Until further research in the form of RCTs with more evidence to support the use of cannabis for lowering IOP, it should not be recommended at this time.”

Noting that the effect that THC has on IOP is short-lived, the authors also added that if patients decide to use cannabis to treat the disease, “they would require frequent dosing, which has the potential to reduce patient adherence and increase side effects of the medication.”

Other research that supports cannabis as a treatment for glaucoma include animal studies that suggested cannabis might improve blood flow to the eyes and promote healing. Animal research also suggests that cannabis may have neuroprotective effects that might prevent damage to the optic nerve.

What About CBD?

However, not all forms of cannabis and glaucoma are effective and shouldn’t be used as a treatment for the disease. A study published in 2006 found that while THC reduced interocular pressure, CBD actually increased IOP. The educational website Glaucoma Today notes that cannabis varietals “with higher THC content can be expected to lower IOP, whereas strains with higher CBD content can be expected to increase IOP. It is therefore important that eye care providers caution patients who are interested in treating their glaucoma with medical cannabis that products with a high CBD content may have a detrimental effect on their disease process.” Patients who choose to treat their glaucoma with cannabis should choose products with negligible amounts of CBD.

Proponents of medical cannabis as a treatment for glaucoma argue that it’s a natural medication with few side effects. Advocates for the glaucoma and marijuana marriage also believe that cannabis can help the pain often associated with glaucoma and reduce the need for surgery. However, the American Academy of Ophthalmology (AAO) maintains that cannabis is not a practical treatment for glaucoma, primarily because of the temporary nature of its effect. The AAO notes that to effectively reduce IOP, patients would have to ingest 18 mg to 20 mg of THC six to eight times daily. The AAO also cites evidence that cannabis might have the opposite effect than intended, increasing IOP and causing additional damage to optic nerve. As a result, the professional group does not recommend the use of cannabis to treat glaucoma.

“Several current, effective treatments for glaucoma are more reliable and safer than marijuana,” the AAO wrote in 2021.