A growing number of studies indicate ketamine works quickly—in a matter of hours—for patients who don't respond to conventional anti-depressants.

But critics say ketamine, originally a horse tranquilizer, hasn't been studied enough—and worry about side effects like confusion, disassociation, elevated blood pressure and muscle tremors. Recreational users of Special K talk about the "K-hole," a state of extreme dissociation, often with visual and auditory hallucinations.

“We don’t know what the long-term side effects of this are,” said Dr. Anthony J. Rothschild of the University of Massachusetts Medical School.

Advocates say pharmaceutical companies are suppressing work on ketamine because, as a generic, it won't bring them any revenue.

Last week, a company called Naurex announced it is working on an injectable drug, GLYX-13, that works like  ketamine but without the side effects—and, of course, it can be patented. There are currently 400 patients in a trial involving GLYX-13  and Naurex expects to get FDA approval in 2019.

That's not soon enough for some patients, who see the risks involved as minor compared to drowning in depression. “I look at the cost of not using ketamine — for me it was certain death,” said Dennis Hartman, a Seattle businessman who began using the drug two years ago, after a lifetime of depression.

The U.S. government classifies ketamine as a Schedule III drug, which means it has moderate to low potential for physical and psychological dependence. And because it's long been approved as an anesthesia doctors are allowed to use ketamine off-label to treat depression

But the $300-$1,000 charge per treatment is rarely covered by insurance, and in many cases its offered by anesthesiologists with no psychiatric background or  psychiatrists with no experience with the drug.

This is hardly the first time so-called party drugs have been reexamined for their therapeutic benefits: Ecstasy, LSD, even marijuana, have all been heralded as TK. But is it good science or bad medicine?

It's hard to argue with the patients who see ketamine as a lifesaver: “Never ever ever before have I felt like that,” said one woman about the first time was given ketamine by her psychiatrist. “I woke up the next morning, and I didn’t take an antidepressant for the first time in 20 years.”  She described feeling transported to a different dimension, where "everything is completely vibrant or molten."