Studies in the 1970s showed that marijuana, when smoked, effectively lowers intraocular pressure. In an effort to determine whether marijuana, or drugs derived from marijuana, might be effective as a glaucoma treatment, the US National Eye Institute supported research studies from 1978 to 1984.

These studies demonstrated that some derivatives of marijuana lowered intraocular pressure when administered orally, intravenously, or by smoking, but not when topically applied to the eye. Many of these studies demonstrated that marijuana — or any of its components — could safely and effectively lower intraocular pressure more than a variety of drugs then on the market.

In 2003 the American Academy of Ophthalmology released a position statement which said that "studies demonstrated that some derivatives of marijuana did result in lowering of IOP when administered orally, intravenously, or by smoking, but not when topically applied to the eye. The duration of the pressure-lowering effect is reported to be in the range of 3 to 4 hours".

However, the position paper qualified that by stating that marijuana was not more effective than prescription medications, stating that "no scientific evidence has been found that demonstrates increased benefits and/or diminished risks of marijuana use to treat glaucoma compared with the wide variety of pharmaceutical agents now available." The first patient in the United States federal government's Compassionate Investigational New Drug program, Robert Randall, was afflicted with glaucoma and had successfully fought charges of marijuana cultivation because it was deemed a medical necessity (U.S. v. Randall) in 1976.

5-HT2A

agonists Peripherally selective 5-HT2A agonists such as the indazole derivative AL-34662 are currently under development and show significant promise in the treatment of glaucoma.