How Does Marijuana Affect Intraocular Pressure (IOP)?
Glaucoma refers to a group of conditions that damage the optic nerve, often due to elevated intraocular pressure (IOP). Lowering IOP is a well-established way to slow disease progression – and marijuana has been shown to do exactly that.
A 1971 study reported that smoking marijuana could reduce IOP by 25 to 30%, lending scientific support to longstanding anecdotal use. Later research confirmed this finding, noting that early interest in marijuana-based treatments was driven in part by the side effects of conventional medications.
Still, not all researchers agree that marijuana should be a first-line therapy. The book Marijuana as Medicine? noted that other glaucoma treatments have since “eclipsed” cannabis – although many still see marijuana as a viable option, especially in complex cases or advanced disease.
Treating Glaucoma: THC vs. CBD
Not all cannabis compounds affect eyes in the same way.
As early as 1981, researchers identified THC as the primary cannabinoid responsible for lowering IOP. However, recent findings suggest that CBD may actually counteract these effects.
According to researchers:
Further evidence shows that while THC formulations significantly reduce IOP, high-dose CBD may temporarily increase it. Based on this research, the American Academy of Ophthalmology advises against using CBD to treat glaucoma.
Marijuana & Glaucoma Studies
Marijuana may offer more than just IOP reduction. Several studies suggest that cannabinoids have neuroprotective and anti-inflammatory effects – which could help prevent optic nerve damage even when pressure is under control.
Researchers have identified three ways cannabis may help protect the eye:
- Glutamate inhibition (reducing oxidative stress on retinal ganglion cells),
- Endothelin inhibition (decreasing vasoconstriction linked to disease progression), and
- Suppression of nitric oxide (which contributes to inflammatory damage).
A review in the Yale Journal of Biology and Medicine concluded:
Recent studies point to marijuana’s interaction with the endocannabinoid system as a key mechanism behind its effects. CB1 receptors have been found in several ocular structures, including the ciliary body, trabecular meshwork, Schlemm’s canal, and retina – all of which play roles in fluid production and drainage.
A study in the European Journal of Neuroscience found significant CB1 expression in human eye tissues, further supporting the theory that cannabis acts directly on the eye (not just via systemic blood pressure changes).
Because of its short half-life and limited corneal penetration, marijuana has not yet been developed into a mainstream ocular treatment. But that could soon change.
New drug formulations, such as THCVHS, are being designed to prolong the IOP-lowering effects of THC. According to researchers, this product may offer both improved pressure control and neuroprotection, helping prevent vision loss even in patients with normal IOP.
The American Academy of Ophthalmology notes:
Medical Cannabis: Limits & Criticism
Despite clear evidence that marijuana lowers IOP, several limitations have raised concerns:
- Marijuana’s IOP-lowering effect is short-lived, lasting just 3-4 hours, which would require frequent dosing throughout the day, and
- Cannabis lowers systolic blood pressure, potentially reducing blood flow to the optic nerve and ocular perfusion pressure (OPP) – both of which are crucial for eye health
However, the relationship between blood pressure and OPP remains under investigation. Some researchers believe that changes in OPP may be driven more by IOP than blood pressure, suggesting that concerns over perfusion may be overstated.
How To Try Medical Marijuana
Glaucoma is the second leading cause of blindness worldwide, affecting over three million Americans – many of whom don’t know they have it.
While marijuana is not a cure, research clearly shows that it lowers IOP and may offer additional neuroprotective benefits. Although its short duration and effects on blood pressure limit its use as a primary treatment, marijuana is widely accepted as a valuable option for late-stage care – especially when conventional therapies fall short.
As always, treatment decisions should be made under the guidance of a qualified physician. To find a CannaMD doctor near you, reach out today!
