It may be of some use in treating glaucoma, or it may be possible to derive a drug from marijuana for this use.
One of the most common reasons that states allow medical marijuana use is to treat and prevent the eye disease glaucoma, which increases pressure in the eyeball, damaging the optic nerve and causing loss of vision.
Marijuana decreases the pressure inside the eye, according to the National Eye Institute: "Studies in the early 1970s showed that marijuana, when smoked, lowered intraocular pressure (IOP) in people with normal pressure and those with glaucoma."
For now, the medical consensus is that marijuana only lowers IOP for a few hours, meaning there's not good evidence for it as a long term treatment right now. Researchers hope that perhaps a marijuana-based compound could be developed that lasts longer.
It may help control epileptic seizures.
Some studies have shown that cannabidiol (CBD), another major marijuana compound, seems to help people with treatment-resistant epilepsy.
A number of individuals have reported that marijuana is the only thing that helps control their or their children's seizures.
However, there haven't been many gold-standard, double-blind studies on the topic, so researchers say more data is needed before we know how effective marijuana is.
It also decreases the symptoms of a severe seizure disorder known as Dravet's Syndrome.
During the research for his documentary "Weed," Sanjay Gupta interviewed the Figi family, who treated their 5-year-old daughter using a medical marijuana strain high in cannabidiol and low in THC.
The Figi family's daughter, Charlotte, has Dravet Syndrome, which causes seizures and severe developmental delays.
According to the film, the drug decreased her seizures from 300 a week to just one every seven days. Forty other children in the state were using the same strain of marijuana to treat their seizures when the film was made — and it seemed to be working.
The doctors who recommended this treatment said the cannabidiol in the plant interacts with brain cells to quiet the excessive activity in the brain that causes these seizures.
Gupta notes, however, that a Florida hospital that specializes in the disorder, the American Academy of Pediatrics, and the Drug Enforcement agency don't endorse marijuana as a treatment for Dravet or other seizure disorders.