Cannabis has been shown to lower intraocular pressure, which is important in glaucoma treatment. However, its effects usually last only 3 to 4 hours. Traditional medications, like eye drops, are also used to lower pressure and tend to last longer with fewer doses per day. 

Cannabis may also cause side effects such as drowsiness or changes in mood, while prescription treatments can have their risks, depending on the type.

Glaucoma sounds like one thing, but it encompasses various eye conditions that damage the optic nerve, typically due to high pressure in the eye. This pressure is called intraocular pressure (IOP). “Intra” refers to the inside and “ocular” to the eye. Controlling IOP and treating glaucoma is very important, and if left untreated, it could lead to blindness. 

Cannabis treatment has gained a lot of popularity in treating glaucoma because of its potential to lower IOP, but on the other hand, traditional glaucoma medications are also effective.¹

What we know about cannabis and IOP

Cannabidiol (CBD) is one of more than 120 natural chemicals made by the Cannabis sativa plant, called phytocannabinoids.² Recently, scientists discovered 21 new types of these chemicals. The two main ones in cannabis are THC, which causes a “high effect,” and CBD, which does not.

Our eyes contain cannabinoid receptors (CB1 and CB2), specifically in the corneal epithelium and endothelium, iris, ciliary body, etc. These receptors are types of proteins because they have affinity (in simple words: they are attracted) for THC and CBD compounds. 

CB1 receptors are mostly found in the brain and help nerve cells to communicate.

CB2 receptors are mainly in the immune system and help regulate inflammation and immune responses.

The first reports of THC lowering eye pressure go back to 1971 when researchers Hepler and Frank found that healthy people had about a 25% drop in intraocular pressure after smoking marijuana.

Research performed after showed similar results, but the effects lasted 4-5 hours.¹

Therefore, this means that a person should use cannabis a few times a day to maintain intraocular pressure at normal levels.

A literature review from 2019 described various forms of cannabis that were used in research, such as:³ 

• Smoking 
• Oral capsules
• Sublingual spray (spraying under the tongue)
• Topical eye drops

Some of the side effects include:

• Dizziness
• Slower reaction
• Increased heart rate
• Mood changes
• Fatigue

Traditional glaucoma medications

Traditional medications like prostaglandin analogues, beta-blockers, and carbonic anhydrase inhibitors help reduce the progression of glaucoma, mostly by helping in fluid drainage out of the eye.⁴ These medications last about 12-24 hours and are applied 1-2 times a day.

Common side effects may include:

• Eye redness or irritation
• Dry eyes or blurred vision
• Changes in eye colour or eyelash growth (especially with prostaglandin analogues)
• Fatigue or slower heart rate (mainly with beta-blockers)

Key differences between cannabis and traditional treatments

Duration of effect

Even though cannabis seems like a very appealing solution, it lasts 4-5 hours, thus needing to be reapplied a few times a day. On the other hand, traditional treatment lasts longer, up to 24 hours.

Method of use

The good part with cannabis is you can choose which method you prefer (smoking, capsules, spray, drops, etc. while traditional medications usually come in the standard eye drops form.

Dosing frequency

Cannabis should be applied more frequently than traditional medications.

Side effects and lifestyle considerations

Both cannabis and traditional medications have side effects, but cannabis can affect daily activities, while the side effects of traditional medications could irritate your eyes.

Availability and regulation

Due to its nature and overuse, cannabis is hard to get in most countries, while traditional medications are available everywhere with a prescription from your doctor.

FAQs: cannabis and glaucoma

Can cannabis replace my glaucoma medication?

Even though it can reduce IOP, it is not recommended as a replacement for glaucoma medication. It is best if you consult with your doctor to decide which treatment suits you the best.

Is smoking cannabis safe for eye health?

Yes, it is safe for eye health. 

Are cannabis-based eye drops available?

Cannabis-based eye drops are being researched, but so far, studies have not proven effective or safe enough for regular glaucoma treatment.

How often would I need to use cannabis to control eye pressure?

According to research, every 4-5 hours. 

Are there legal or medical risks involved?

Yes. Cannabis laws vary widely by location, and medical risks include side effects and potential interactions with other medications. Always consult a healthcare professional before considering cannabis for glaucoma.

Potential role of cannabis in the future

There is a lot of interest in cannabis eye treatments, not just for glaucoma but for other eye conditions as well, like keratitis, uveitis, diabetic neuropathy, etc.

Researchers are exploring how cannabinoids, especially CBD and THC, may help reduce inflammation, pain, and oxidative stress in the eyes. Early studies suggest that these compounds could play a protective role in the retina and optic nerve, potentially slowing disease progression in certain conditions.

In the future, cannabis-based eye drops, gels, or sustained-release implants may become viable treatment options. However, more clinical research is needed to determine safe and effective dosages, as well as to address challenges like drug delivery and long-term side effects. As regulations evolve and scientific understanding deepens, cannabis could become an important part of ophthalmic care.

Summary

Glaucoma refers to a group of eye conditions that damage the optic nerve, often due to high intraocular pressure (IOP). Managing IOP is essential to prevent vision loss or blindness. While traditional medications like prostaglandin analogues, beta blockers, and carbonic anhydrase inhibitors are standard treatments, interest in cannabis for glaucoma is growing due to its IOP-lowering potential.

Cannabis, particularly THC, has been shown to reduce IOP by about 25%, but the effects only last 3-4 hours, requiring multiple daily doses. In contrast, traditional eye drops typically last 12-24 hours with fewer applications. Cannabinoids interact with CB1 and CB2 receptors found in the eyes, which may explain their effect on pressure and inflammation.

Studies since the 1970s have explored various cannabis delivery methods like smoking, oral capsules, sublingual sprays, and eye drops. However, cannabis can cause side effects such as dizziness, increased heart rate, mood changes, and fatigue, which may interfere with daily activities.

Traditional glaucoma medications, while also having side effects like eye redness, dry eyes, and, in some cases, changes in eye colour or slower heart rate, are generally better tolerated and easier to access with a prescription.

Though cannabis is not currently recommended as a replacement for glaucoma medication, ongoing research is exploring its broader role in eye care. Cannabinoids may help with conditions like keratitis, uveitis, and diabetic neuropathy by reducing inflammation and protecting retinal cells.

Future treatments might include cannabis-based eye drops or implants, but more studies are needed to ensure safety and efficacy. Until then, cannabis remains a potential supplemental therapy, one that should be considered carefully with guidance from a healthcare provider.