Marijuana use can be used 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."

These effects of the drug may slow the progression of the disease, preventing blindness.

There's a fair amount of evidence that marijuana does no harm to the lungs, unless you also smoke tobacco, and one study published in Journal of the American Medical Association found that marijuana not only doesn't impair lung function, it may even increase lung capacity.

Researchers looking for risk factors of heart disease tested the lung function of 5,115 young adults over the course of 20 years. Tobacco smokers lost lung function over time, but pot users actually showed an increase in lung capacity.

It's possible that the increased lung capacity may be due to taking a deep breaths while inhaling the drug and not from a therapeutic chemical in the drug.

Those smokers only toked up a few times a month, but a more recent survey of people who smoked pot daily for up to 20 years found no evidence that smoking pot harmed their lungs.

Marijuana use can prevent epileptic seizures in rats, a 2003 study showed.

Robert J. DeLorenzo, of Virginia Commonwealth University, gave marijuana extract and synthetic marijuana to epileptic rats. The drugs rid the rats of the seizures for about 10 hours. Cannabinoids like the active ingredients in marijuana, tetrahydrocannabinol (also known as THC), control seizures by binding to the brain cells responsible for controlling excitability and regulating relaxation.

The findings were published in the Journal of Pharmacology and Experimental Therapeutics.

During the research for his documentary "Weed," Sanjay Gupta interviewed the Figi family, who treats their 5-year-old daughter using a medical marijuana strain high in cannabidiol and low in THC.

There are at least two major active chemicals in marijuana that researchers think have medicinal applications (there are up to 79 known active compounds). Those two are cannabidiol (CBD) — which seems to impact the brain mostly without a high— and tetrahydrocannabinol (THC) — which has pain relieving (and other) properties.

The Figi family's daughter, Charlotte, has Dravet Syndrome, which causes seizures and severe developmental delays.

According to the film, the drug has decreased her seizures from 300 a week to just one every seven days. Forty other children in the state are using the same strain of marijuana (which is high in CBD and low in THC) to treat their seizures — and it seems to be working.

The doctors who recommended this treatment say that the cannabidiol in the plant interacts with the brain cells to quiet the excessive activity in the brain that causes these seizures.

As Gutpa notes, 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.

CBD may also help prevent cancer from spreading, researchers at California Pacific Medical Center in San Francisco reported in 2007.

Cannabidiol stops cancer by turning off a gene called Id-1, the study, published in the journal Molecular Cancer Therapeutics, found. Cancer cells make more copies of this gene than non-cancerous cells, and it helps them spread through the body.

The researchers studied breast cancer cells in the lab that had high expression levels of Id-1 and treated them with cannabidiol. After treatment the cells had decreased Id-1 expression and were less aggressive spreaders. But beware: these are studies on cancer cells in the lab, not on cancer patients.

Other very preliminary studies on aggressive brain tumors in mice or cell cultures have shown that THC and CBD can slow or shrink tumors at the right dose, which is a great reason to do more research into figuring out that dose.

One 2014 study found that marijuana can significantly show the growth of the type of brain tumor associated with 80% of malignant brain cancer in people.

In "WEED," Gupta also mentioned a few studies in the U.S., Spain, and Israel that suggest the compounds in cannabis could even kill cancer cells.

Medical marijuana users claim the drug helps relieve pain and suppress nausea — the two main reasons it's often used to relieve the side effects of chemotherapy.

In 2010, researchers at Harvard Medical School suggested that that some of the drug's benefits may actually be from reduced anxiety, which would improve the smoker's mood and act as a sedative in low doses.

Beware, though, higher doses can increase anxiety and make you paranoid.

Marijuana may be able to slow the progression of Alzheimer's disease, a study led by Kim Janda of the Scripps Research Institute suggests.

The 2006 study, published in the journal Molecular Pharmaceutics, found that THC, the active chemical in marijuana, slows the formation of amyloid plaques by blocking the enzyme in the brain that makes them. These plaques seem to be what kill brain cells and potentially cause Alzheimer's.

A synthetic mixture of CBD and THC seem to preserve memory in a mouse model of Alzheimer's disease. Another study suggested that in population-based studies, a THC-based prescription drug called dronabinol was able to reduce behavioral disturbances in dementia patients.

Marijuana may ease painful symptoms of multiple sclerosis, a study published in the Canadian Medical Association Journal in May suggests.

Jody Corey-Bloom studied 30 multiple sclerosis patients with painful contractions in their muscles. These patients didn't respond to other treatments, but after smoking marijuana for a few days they reported that they were in less pain.

The THC in the pot binds to receptors in the nerves and muscles to relieve pain. Other studies suggest that the chemical also helps control the muscle spasms.

Other types of muscle spasms respond to marijuana as well. Gupta also found a teenager named Chaz who was using medical marijuana to treat diaphragm spasms that were untreatable by other, prescribed and very strong, medications.

His condition is called myoclonus diaphragmatic flutter (also known as Leeuwenhoek's Disease) and causes non stop spasming in the abdominal muscles which are not only painful, but interfere with breathing and speaking.

Smoking marijuana was able to calm the attacks almost immediately, at least it seemed to in this patient.

Treatment for hepatitis C infection is harsh — negative side effects include fatigue, nausea, muscle aches, loss of appetite, and depression — and lasts for months. Many people aren't able to finish their treatment course because of the side effects.

But, pot to the rescue: A 2006 study in the European Journal of Gastroenterology and Hepatology found that 86% of patients using marijuana successfully completed their Hep C therapy, while only 29% of non-smokers completed their treatment, possibly because the marijuana helps lessens the treatments side effects.

Marijuana also seems to improve the treatment's effectiveness: 54% of hep C patients smoking marijuana got their viral levels low and kept them low, in comparison to only 8% of nonsmokers.

Patients with inflammatory bowel diseases like Crohn's disease and ulcerative colitis could benefit from marijuana use, studies suggest.

University of Nottingham researchers found in 2010 that chemicals in marijuana, including THC and cannabidiol, interact with cells in the body that play an important role in gut function and immune responses. The study was published in the Journal of Pharmacology and Experimental Therapeutics.

THC-like compounds made by the body increase the permeability of the intestines, allowing bacteria in. The plant-derived cannabinoids in marijuana block these body-cannabinoids, preventing this permeability and making the intestinal cells bond together tighter.

One study in Israel showed that smoking a joint significantly reduced Crohn's disease symptoms in 10 out of 11 patients compared to a placebo and without side effects.

That's a small study, but other research has shown similar effects. Even more research finds that people with Crohn's and other inflammatory bowel disorders use cannabis to help deal with their symptoms, even if there are questions about how much marijuana can or can't help.

Marijuana alleviates pain, reduces inflammation, and promotes sleep, which may help relieve pain and discomfort for people with rheumatoid arthritis, researchers announced in 2011.??

Medical marijuana is also being used to treat the autoimmune disease Systemic Lupus Ertyhematosus, which is when the body starts attacking itself for some unknown reason.

Researchers from rheumatology units at several hospitals gave their patients Sativex, a cannabinoid-based pain-relieving medicine. After a two-week period, people on Sativex had a significant reduction in pain and improved sleep quality compared to placebo users.

A study published in the American Journal Of Medicine on April 15 of 2013 suggested that pot smokers are skinnier than the average person and have healthier metabolism and reaction to sugars, even though they do end up eating more calories.

The study analyzed data from more than 4,500 adult Americans — 579 of whom were current marijuana smokers, meaning they had smoked in the last month. About 2,000 had used marijuana in the past, while another 2,000 had never used the drug.

They studied their body's response to eating sugars: their levels of the hormone insulin and their blood sugar levels while they hadn't eaten in nine hours, and after eating sugar.

Not only were the pot users skinnier, but their body had a healthier response to sugar.

Contrary to stoner stereotypes, marijuana usage has actually been shown to have some positive mental effects, particularly in terms of increasing creativity. Even though people's short-term memories tend to function worse when high, people get better at tests requiring them to come up with new ideas.

One study tested participants on their ability to come up with different words related to a concept, and found that using cannabis allowed people to come up with a greater range of related concepts, seeming "to make the brain better at detecting those remote associations that lead to radically new ideas," according to Wired.

Other researchers have found that some participants improve their "verbal fluency," their ability to come up with different words, while using marijuana.

Part of this increased creative ability may come from the release of dopamine in the brain, lessening inhibitions and allowing people to feel more relaxed, giving the brain the ability to perceive things differently.

Recent research from Israel shows that smoking marijuana significantly reduces pain and tremors and improves sleep for Parkinson's disease patients. Particularly impressive was the improved fine motor skills among patients.

Medical marijuana is legal in Israel for multiple conditions, and a lot of research into the medical uses of cannabis is done there, supported by the Israeli government.

The Colorado Department of Public Health recently awarded $2 million to the Multidisciplinary Association for Psychedelic Studies (MAPS is one of the biggest proponents of marijuana research) to study marijuana's potential as part of treatment for people with post-traumatic stress disorder.

Marijuana is approved to treat PTSD in some states already — in New Mexico, PTSD is the number one reason for people to get a license for medical marijuana.

Naturally occurring cannabinoids, similar to THC, help regulate the system that causes fear and anxiety in the body and brain.

But there are still questions about the safety of using marijuana while suffering from PTSD, which this study will hopefully help answer.

Research from the University of Nottingham shows that marijuana may help protect the brain from damage caused by stroke, by reducing the size of the area affected by the stroke — at least in rats, mice, and monkeys.

This isn't the only research that has shown neuroprotective effects from cannabis. Some research shows that the plant may help protect the brain after other traumatic events, like concussions. [link here? actually since we go in depth on that one in the next slide, maybe flush out the stroke angle more here instead.]

There is some evidence that marijuana can help heal the brain after a concussion or other traumatic injury. A recent study in the journal Cerebral Cortex showed that in mice, marijuana lessened the bruising of the brain and helped with healing mechanisms after a traumatic injury.

Harvard professor emeritus of psychiatry and marijuana advocate Lester Grinspoon recently wrote an open letter to NFL Commissioner Roger Goodell, saying the NFL should stop testing players for marijuana, and that the league should start funding research into the plant's ability to protect the brain.

"Already, many doctors and researchers believe that marijuana has incredibly powerful neuroprotective properties, an understanding based on both laboratory and clinical data," he writes.

Goodell recently said that he'd consider permitting athletes to use marijuana if medical research shows that it's an effective neuroprotective agent.

This is a complicated one, because it involves effects that can be both positive and negative. Marijuana disturbs sleep cycles by interrupting the later stages of REM sleep. In the long run, this could be a problem for frequent users.

However, for people suffering from serious nightmares, especially those associated with PTSD, this can be helpful. Nightmares and other dreams occur during those same stages of sleep. By interrupting REM sleep, many of those dreams may not occur. Research into using a synthetic cannabinoid, like THC, but not the same, showed a significant decrease in the number of nightmares in patients with PTSD.

Additionally, even if frequent use can be bad for sleep, marijuana may be a better sleep aid than some other substances that people use. Some of those, including medication and alcohol, may potentially have even worse effects on sleep, though more research is needed on the topic.

One of the most well-known medical uses of marijuana is for people going through chemotherapy.

Cancer patients being treated with chemo suffer from painful nausea, vomiting, and loss of appetite. This can cause additional health complications.

Marijuana can help reduce these side effects, alleviating pain, decreasing nausea, and stimulating the appetite. There are also multiple FDA-approved cannabinoid drugs that use THC, the main active chemical in marijuana, for the same purposes.

Marijuana is safer than alcohol. That's not to say it's completely risk free, but it's much less addictive and doesn't cause nearly as much physical damage.

Disorders like alcoholism involve disruptions in the endocannabinoid system. Because of that, some people think cannabis might help patients struggling with those disorders.

Research in Harm Reduction Journal shows that some people use marijuana as a less harmful substitute for alcohol, prescription drugs, and other illegal drugs. Some of the most common reasons for patients to make that substitution are the less adverse side effects from marijuana and the fact that it is less likely to cause withdrawal problems.

Some people do become psychologically dependent on marijuana, and this doesn't mean that it's a cure for substance abuse problems. But, from a harm-reduction standpoint, it can help.

What Marijuana Does To Your Body And Brain »