It's been more than two decades since California became the first state in America to legalize the use of marijuana for medical purposes. Since then, 29 states and the District of Columbia have followed suit, and seven states have taken the matter further, legalizing the drug's recreational use.

It's a complicated state of affairs because although states have given residents and doctors the green light to use marijuana in a variety of ways, the federal government has lagged behind. Marijuana remains on the Drug Enforcement Administration's list of Schedule I narcotics — a list reserved for drugs that are deemed to have a high potential for abuse and no medically accepted use in the United States.

The list includes substances like heroin, LSD, ecstasy and peyote.

Being on the list has severely hampered scientific research into the uses and properties of marijuana, and marijuana and its oils have not been approved by the Food and Drug Administration for any medical use.

Nevertheless, the drug has begun to emerge in many states as a potential medication for a variety of conditions — mostly buttressed by anecdotal success stories that can often sound miraculous. And Dronabinol, a pharmaceutical form of THC, the psychoactive compound in marijuana, and a man-made cannabinoid drug called nabilone have been approved by the FDA to treat some conditions.

But what about breast cancer? Will medical marijuana emerge as a treatment for what the American Cancer Society says is the most common cancer found in American women?

According to the American Cancer Society, one in eight women will be diagnosed with breast cancer during her lifetime.

And while cannabis has shown to be very effective in treating nausea and vomiting — both typical side effects of conventional breast cancer treatments like chemotherapy — scientists looking into the possibility of the drug having broader applications say that recent studies have also shown that cannabis contains a non-toxic, non-psychoactive compound that may block the progress of metastatic breast cancer.

Researchers at the California Pacific Medical Center Research Institute in San Francisco say the compound, called cannabidiol (CBD), was used in lab tests to inhibit activity in the gene believed to be responsible for driving the growth of cancer cells.

That gene, Id-1, helps drive embryonic growth in humans, but after birth it is only found in metastatic cancer cells, said lead researcher Sean D. McAllister, an associate scientist at the center. The group has been searching for a way to “turn them off,” McAllister said, and according to the results of their study — which was published in the November 2007 issue of Molecular Cancer Therapeutics — CBD does exactly that.

“The cancer cell itself is not the problem, because a tumor can be removed through surgery,” he said. “The problem is the development of metastatic cells, which is conducted by Id-1.”

Researchers' results, which McAllister called “a serendipitous discovery” after about a dozen years of research on the Id-1 gene, came during tests on cells, not in live humans.

Clinical trials in live patients could result in different results, researchers say, but their work is still a baseline that shows CBD could be a potential treatment to slow the growth and reduce the invasiveness of aggressive, metastatic cancers that medical science struggles to treat.

In 2012, McAllister's team took the next step and researched how CBD affected cancer in animals, finding that the plant compounds may also have anti-tumor effects. But the work is still preliminary, and more work needs to be done to further understand CBDs.

The bottom line, say doctors and cancer patient advocacy groups, is that cannabis is, at best, a complementary treatment for patients already involved in conventional breast cancer treatments. The American Cancer Society calls the drug an effective treatment for nausea or nerve pain associated with chemo-induced peripheral neuropathy, but strongly warns cancer patients against treating the drug as a one-size-fits-all treatment for breast cancer.

“Relying on marijuana alone as treatment while avoiding or delaying conventional medical care for cancer may have serious health consequences,” the American Cancer Society says on its website.