Ketamine, or "Special K" as it is commonly known, is a psychedelic party drug that causes hallucinations. You're most likely to hear about it in a context of drug abuse these days, so you might be shocked to hear that some doctors around the country are now using ketamine off-label to manage patients with severe, treatment-resistant depression.

In fact, ketamine was not always bad, it has a medicinal history. Ketamine was once an FDA-approved drug back in the 1970s. It was known to be a fast-acting general anesthetic. Although the drug is not approved to treat depression, here's everything you should know about its possible new use.

In 2006 experts at the National Institute of Mental Health (NIMH) discovered that a single dose of intravenous ketamine can led to a strong antidepressant effects within hours. The study was like a breath of fresh air, given that current antidepressants; like Lexapro or Prozac takes weeks to take effect.

What's more, the people who participated in the study had what's called treatment-resistant depression, which imply ketamine could help people who don't respond to traditional medications and therapy, including electroconvulsive therapy (ECT), which is used for severe depression. Another study done in 2013 reported similar hasty results. And last year, the director of the NIMH, Tom Insel, MD, published in his blog that recent data suggest intravenous ketamine may be the most important improvement in antidepressant treatment in years.

So this got us thinking, if it was an important improvement, why are some saying there is a problem? There are about hundreds or thousands of unanswered questions about who it might work for, and if it's really safe. In a New York Times story last year, Dominic A. Sisti, an assistant professor of medical ethics at the University of Pennsylvania, said he is concerned about clinics that are run by anesthesiologists who don't offer psychiatric treatment; and clinics opened by psychiatrists who might not have enough experience with ketamine.