Health Topics — Neurological
Glaucoma and Cannabinoids: Intraocular Pressure and Optic Nerve Research
One of the oldest lines of cannabinoid research — what four decades of intraocular pressure studies have found, why the findings haven't translated to clinical use, and what a newer neuroprotective angle adds to the picture.
Procedural Note
Glaucoma is a serious eye condition and a leading cause of irreversible blindness worldwide. It is managed under the care of an ophthalmologist. Nothing in this article constitutes guidance on managing glaucoma or intraocular pressure. People with glaucoma or elevated intraocular pressure should work with their eye care provider on treatment decisions. All findings discussed are preclinical or from early human observations unless explicitly stated otherwise.
The observation that cannabis lowers eye pressure is one of the oldest findings in cannabinoid research — documented in the 1970s, studied seriously through the 1980s and 1990s, and ultimately set aside by ophthalmology not because it wasn't real, but because it wasn't practical. Understanding why is as important as understanding what the research found.
What Glaucoma Is and Why Intraocular Pressure Matters
Glaucoma is not a single disease but a group of conditions that damage the optic nerve — the bundle of nerve fibers that carries visual information from the eye to the brain. It is the second leading cause of blindness worldwide, affecting an estimated 80 million people. Most forms of glaucoma are associated with elevated intraocular pressure (IOP) — the fluid pressure inside the eye. The eye continuously produces aqueous humor, a clear fluid that maintains the eye's shape and nourishes its internal structures. When the drainage channels through which this fluid exits become impaired, pressure builds and gradually damages the optic nerve.
The optic nerve is composed of retinal ganglion cells — specialized neurons whose axons, the long projecting fibers through which neurons send signals, bundle together to form the optic nerve. These cells are the point at which elevated IOP causes harm: sustained high pressure reduces blood supply to the nerve, leads to mechanical compression of axons, and triggers a cascade of neuronal death that, once begun, continues even if pressure is subsequently normalized. The damage is irreversible. Current glaucoma treatment focuses on lowering IOP to slow progression, not on reversing damage already done.
This neuronal component is why glaucoma research appears in the Neurological Health pillar rather than under ophthalmology alone. The death of retinal ganglion cells under sustained IOP is a form of neurodegeneration — the same class of processes involving oxidative stress, excitotoxicity, and inflammatory cell activation that appear in Parkinson's, Huntington's, and other neurodegenerative conditions. This opens a second research angle beyond pressure reduction: can the optic nerve's neurons be protected from pressure-induced death even when IOP itself is not fully controlled?
The Cannabinoid IOP Research Lineage
The observation that cannabis use reduces intraocular pressure was first reported in human subjects in 1971 by Hepler and Frank — a finding that attracted immediate research interest given the clinical need for IOP-lowering treatments in glaucoma. Subsequent work across the 1970s and 1980s confirmed the IOP-lowering effect of THC in multiple human studies and characterized it in animal models. CBG entered this literature specifically through the work of Colasanti and colleagues at West Virginia University, whose studies in feline and rodent models documented that CBG — administered topically to the eye — reduced IOP significantly.
Colasanti et al. (1984, 1990) — Feline and Rodent Models: Colasanti's research group examined multiple cannabinoids for IOP-lowering activity in cat and rat eye models. CBG produced statistically significant reductions in IOP following topical ocular application — reductions comparable to those seen with THC in the same models. The effect was dose-dependent and reversible, peaking within one to two hours of application and returning to baseline within four to six hours.
Mechanism: The IOP-lowering mechanism is not fully resolved but involves reduced production of aqueous humor and possibly increased outflow through the trabecular meshwork — the eye's primary drainage channel. CB1 receptors are expressed in the ciliary body (the structure that produces aqueous humor), the trabecular meshwork, and other ocular tissues, suggesting a receptor-mediated mechanism. Whether CBG's IOP effect operates primarily through CB1, through other receptor pathways, or through a combination is not fully established in the literature.
Significance: The Colasanti work established CBG as an IOP-lowering compound in animal models and placed it within the broader cannabinoid glaucoma research literature. It is the primary citation for CBG's glaucoma research profile. The studies are animal models from the 1980s and 1990s — their methodology reflects the research standards of that era. No human clinical trials of CBG for glaucoma exist as of 2026.
Why the IOP Research Didn't Translate to Clinical Use
The cannabinoid IOP-lowering effect is real and has been replicated across multiple studies spanning decades. The reason ophthalmology did not pursue cannabinoids as glaucoma treatments is not scientific skepticism about the finding — it is a set of practical and clinical limitations that made cannabinoids poor candidates compared to existing treatments.
The Neuroprotective Angle — A Different Research Question
The more scientifically active current research question is not whether cannabinoids lower IOP — that is established in preclinical systems — but whether they can protect retinal ganglion cells from pressure-induced death through neuroprotective mechanisms independent of IOP reduction. This reframes the research from a pressure management question to a neurodegeneration question, and it is where CBG's broader neuroprotective mechanisms become relevant.
Retinal ganglion cell death in glaucoma involves oxidative stress, excitotoxicity (damage from excessive glutamate signaling), and neuroinflammation — the same processes that characterize neurodegeneration in the brain. CB1 and CB2 receptors are expressed in retinal ganglion cells and in the retinal Müller glia — supporting cells that modulate the neuroinflammatory environment of the retina. Cannabinoid receptor activation in these cells has been associated with reduced excitotoxic damage and reduced inflammatory cytokine production in preclinical retinal models, suggesting a neuroprotective pathway that does not depend on IOP reduction.
CBG's documented mechanisms — antioxidant activity, CB2 partial agonism with anti-inflammatory properties, PPAR-γ activation — are all relevant to this neuroprotective angle. None of them have been specifically studied in retinal ganglion cell or glaucoma models for CBG directly. The mechanistic fit is coherent; the direct research does not yet exist.
What the Research Amounts To for CBG Specifically
CBG has documented IOP-lowering activity in feline and rodent animal models from the Colasanti research group — findings that are real, replicated within that research program, and consistent with the broader cannabinoid IOP literature. Those findings are three to four decades old, have not been extended to human clinical trials, and exist in a research context where the IOP-lowering approach itself was ultimately set aside by clinical ophthalmology for practical reasons. The neuroprotective angle is mechanistically interesting and represents where modern cannabinoid glaucoma research is headed, but CBG has not been directly studied in retinal neuroprotection models. The honest summary is that CBG has a historically documented preclinical finding in a research area where translation has been slow and complicated, and a set of mechanisms relevant to where that research is now going.
References
- Colasanti, B.K., Brown, R.E., & Craig, C.R. (1984). Ocular hypotension, ocular toxicity, and neurotoxicity in response to marihuana extract and cannabidiol. General Pharmacology, 15(6), 479–484.
- Colasanti, B.K. (1990). A comparison of the ocular and central effects of delta 9-tetrahydrocannabinol and cannabigerol. Journal of Ocular Pharmacology, 6(4), 259–269.
- Hepler, R.S., & Frank, I.R. (1971). Marihuana smoking and intraocular pressure. JAMA, 217(10), 1392.
- Nucci, C., Gasperi, V., Tartaglione, R., et al. (2007). Involvement of the endocannabinoid system in retinal damage after high intraocular pressure–induced ischemia in rats. Investigative Ophthalmology & Visual Science, 48(7), 2997–3004.
- Porcella, A., Maxia, C., Gessa, G.L., & Pani, L. (2001). The synthetic cannabinoid WIN55212-2 decreases the intraocular pressure in human glaucoma resistant to conventional therapies. European Journal of Neuroscience, 13(2), 409–412.
- Yazulla, S. (2008). Endocannabinoids in the retina: From marijuana to neuroprotection. Progress in Retinal and Eye Research, 27(5), 501–526.
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