Inhaling cannabis significantly reduces intraocular pressure (IOP) in healthy subjects for approximately four hours, according to data published in the journal Frontiers in Medicine

An international team of researchers from the United States and Italy assessed the association between THC plasma levels and IOP in a cohort of healthy adults following the self-administration of cannabis cigarettes containing either six percent or 13 percent THC. 

Consistent with prior research, marijuana inhalation resulted in a temporary reduction in IOP. IOP reduction was most significant 60 minutes after smoking but remained below subjects’ normal baseline for up to four hours. THC/plasma concentrations of 20ng/ml, but not above this level, were most strongly correlated with decreases in IOP. 

“The results of this study indicate that in healthy adult subjects, inhaled THC significantly lowers IOP, and that this effect correlates with plasma THC levels,” authors reported. “IOP reduction occurred soon after inhalation and was reduced by as much as 16 percent. … Furthermore, increasing plasma levels up to a concentration of 20 ng/ml was strongly correlated with increasing reduction in IOP. THC plasma levels >20 ng/ml were not correlated with further reduction in IOP.”

Scientists have long documented that THC inhalation reduces intraocular pressure. According to recently published survey data, over one-third of glaucoma patients have discussed their medical use of cannabis with their oncologists. (Glaucoma is typically caused by abnormally high pressure within the eye.) Nevertheless, the American Glaucoma Society has not endorsed the use of cannabis as a treatment for glaucoma. By contrast, virtually all state-specific medical access laws specify glaucoma as a qualifying medical condition.

Full text of the study, “The relationship between plasma tetrahydrocannabinol levels and intraocular pressure in healthy adult subjects,” appears in Frontiers in Medicine.

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