On Tuesday, Colorado and Washington became the first two states to legalize recreational use of marijuana. The referendums come at a time when more than a third of states have approved the cannabis plant for medicinal purposes.

Proponents for legalizing marijuana tout its pain-relieving benefits and use by cancer patients undergoing chemotherapy or radiation treatments; opponents stress that science has yet to prove the drug is safe.

It's a bit like the fairytale, "Jack and the Beanstalk." This "magic" plant that could help with everything from glaucoma to ALS, or Lou Gehrig's disease, could also contain unknown dangers to our heart, lungs and brain.

The real question is, if we legalize marijuana, will we all live happily ever after?

The Drug Enforcement Administration lists (PDF) marijuana under the Schedule I category of controlled substances, meaning it has a high potential for abuse, has no currently accepted medical use in the United States and is not deemed safe for use.

The DEA's stance has made it difficult for scientists to push forward national clinical trials on the drug. In 2009, the American Medical Association urged the government to review marijuana's classification with "the goal of facilitating the conduct of clinical research and development of cannabinoid-based medicines" to no avail.

Still, in the last three years, more than 6,000 studies have been published in scientific journals about the cannabis plant, according to NORML, an organization that works to legalize marijuana. Much of the research has focused on the plant's effects on the body's endocannabinoid system.

The endocannabinoid system acts like a bridge between mind and body, helping different types of cells communicate with each other.

Our bodies make natural cannabinoids, or active chemicals that cause drug-like effects through the body, according to the National Cancer Institute. The main psychoactive ingredient in marijuana -- delta-9-tetrahydrocannabinol, or THC -- works in the same way as these natural chemicals.

Dr. Julie Holland, author of "The Pot Book," says medicinal marijuana is most often prescribed to combat nausea and stimulate appetite. It is also prescribed to manage chronic pain.

The Food and Drug Administration has approved two synthetic cannabinoid drugs for use in patients with extreme nausea: dronabinol and nabilone. Another, Sativex, is undergoing phase III clinical trials in the United States for the treatment of cancer pain.

A series of trials published by the University of California Center for Medicinal Cannabis Research in May showed cannabis can help patients suffering from neuropathic pain, commonly caused by degenerative diseases like multiple sclerosis or fibromyalgia. Neuropathic pain is also a common side effect of chemotherapy and radiation.

Study participants on cannabis reported a 34 to 40% decrease in pain compared to the 17 to 20% decrease seen from patients on a placebo drug.

Another study, published in the British Medical Journal in February, found a lower prevalence of Type II diabetes in marijuana users. The researchers hypothesized that cannabis lowers the risk for diabetes due to its immunomodulatory and anti-inflammatory properties.

Even with all its potential benefits, cannabis should not be viewed as a harmless substance, NORML says.

The drug's active constituents "may produce a variety of physiological and euphoric effects," the organization's website states. "As a result, there may be some populations that are susceptible to increased risks."

The National Institute on Drug Abuse says that marijuana causes an increase in heart rate, which could put users at risk for a heart attack or stroke. Marijuana smoke also contains carcinogens similar to cigarette smoke.

A 2011 study published in the journal Addiction found marijuana has little long-term effect on learning and memory, according to TIME.com. The study authors followed nearly 2,000 Australian adults, aged 20 to 24, for eight years. They concluded that the adverse impacts of cannabis use (shown in earlier studies) were either related to pre-existing factors or were reversible after even extended periods of use.

Yet a similar study out of New Zealand earlier this year showed the opposite may be true for adolescent marijuana users.

The researchers found that teens who smoked pot heavily (at least four days a week) lost an average of eight IQ points between the ages of 13 and 38. Adults who had smoked as teens tended to show more pronounced deficits in memory, concentration, and overall brainpower in relation to their peers.