Ketamine has been around as an anesthetic since 1970, but in recent years it has been popular as an especially powerful club or rave drug that creates intense, short-term hallucinations, dissociation and other psychotomimetic effects. Commonly known as Special K or Vitamin K, it so overwhelms some users that they refer to the experience as going down the K-hole.

But there's increasing evidence that ketamine could be a fast and effective treatment for depression. There are even full-page ads in the New York Times touting it as a drug that "could change how depression is treated overnight."

"Researchers found ketamine can relieve depressive symptoms within 24 hours, whereas traditional treatments can take weeks or even months to reduce symptoms, said the ad from Mount Sinai Hospital. "It's a huge breakthrough, to say the least."

Mount Sinai isn't alone in hopping on the ketamine bandwagon. According to Anesthesiology News, anesthesiologists across the country are opening private clinics to provide off-label infusions or injections of the drug to patients suffering from treatment resistant depression, both unipolar and bipolar, as well as post-traumatic stress disorder, suicidal ideation, anxiety, and other disorders. Psychiatrists and other physicians are starting to open them, too.

It isn't cheap, and most health insurance doesn't cover it because ketamine has not been approved by the FDA for use as an antidepressant, only as an anesthetic. The cost per infusion or injection is typically $500 or more, and typically takes one every other day for two weeks, with further injections every few weeks, so the out-of-pocket costs can be considerable. But given the results—quickly lifting many patients out of crippling depression—the price tag may well be worth it. After all, traditional antidepressants take a month or longer to work, and even then help only a minority of patients.

"The results are amazing," said anesthesiologist Glen Z. Brooks, founder and medical director of New York Ketamine Infusions LLC, in New York City, and one of the pioneers in the field. His success rate averages about 65% when measured by standardized mood and function surveys, and is even greater for younger adults, he said.

"The procedure is very well tolerated. We have seen no complications during or after the 45-minute infusions in now close to 8,000 treatments," Brooks told Anesthesiology News. "I have been treating some patients for as long as three years with ongoing remission of their symptoms, so efficacy can be very long term."

"We notice a 50% improvement in depression scores within the first three infusions, which take six days," said anesthesiologist Enrique Abreu, medical director at Portland Ketamine Clinic in Oregon. "Overall, 75% to 80% of patients see improvement in depression, mood and anxiety after six treatments," he told Anesthesiology News.

New Jersey psychiatrist Steven Levine decided to explore ketamine after reading reports of clinical studies conducted at the National Institute of Mental Health. "The results were unlike anything we had seen before, with positive outcomes emerging within days or weeks. Some really sick people were getting significantly better within hours. I couldn’t convince myself to not do it."

Levine asked several anesthesiologists about possible dangers of ketamine before opening his clinic. "They were totally nonplussed about the low dosage used in the infusion, unconcerned about any potential for bad side effects," he told Anesthesiology News. "They were used to giving it in much higher doses for anesthesia and even higher doses in burn units when changing dressings."

While the doses are low compared to anesthetic doses, patients still report some of the weird effects known to recreational users, although to a lesser degree. Anesthesiology News reported that "patients remain awake or in a twilight state. Dizziness or a sensation of dissociation is common, and generally disappears shortly after the infusion," while a recent National Public Radio report on a successful ketamine patient described "an altered sense of reality for an hour or two after taking the drug."

The interest in ketamine as an antidepressant is grounded in recent scientific research, particularly the groundbreaking 2006 NIMH study that showed ketamine produced "rapid and robust anti-depressant effects" within a couple of hours of a first injection. In 2012, researchers writing in Science called the finding "arguably the most important discovery in half a century." Several other studies since then shown ketamine to be efficacious for reducing suicidal ideation, depression, and other anxiety disorders.

Not everybody is on board, though. "While the science is promising, ketamine is not ready for broad use in the clinic, NIMH director Tom Insel wrote in an October blog post.

The American Psychiatric Association's Task Force on Novel Biomarkers and Treatments is also urging caution. "The antidepressant efficacy of ketamine … holds promise for future glutamate-modulating strategic," the task force noted in a research review and meta-analysis, but "the fleeting nature of ketamine’s therapeutic benefit, coupled with its potential for abuse and neurotoxicity, suggest that its use in the clinical setting warrants caution."

The American Society of Anesthesiologists is keeping a watchful eye out, it told Anesthesiology News. "The American Society of Anesthesiologists is committed to promoting the highest standards of care for the patients they serve. This new practice area has been brought to ASA’s attention and will be carefully reviewed."

But for thousands of patients, ketamine has proven itself—at least for now. For Paul, the patient in the NPR story, it was a lifesaver: "If there was even a 1 percent chance that this worked, it would have been worth it to me. My life was hanging in the balance," he said. The benefits were immediate and tremendous: "I remember I was in my bathroom and I literally fell to my knees crying because I had no anxiety, I had no depression," he said.

Some patients have organized the Ketamine Advocacy Network, which works with patients and practitioners to help the field gain legitimacy. The network list some 18 ketamine practitioners in the U.S., only about a third of the estimated number of clinics operating. It excludes some because of excessive costs or requirements for additional tests for which clinical evidence is lacking.

Who would have thought? Now the treatment of depression is going through the K-hole.