It was an anesthetic for animals and people became a potent battlefield pain reliever in Vietnam and morphed into the trippy club drug Special K. Now the chameleon drug ketamine is finding new life as an unapproved treatment for depression and suicidal behavior.

Clinics have opened around the United States promising instant relief with their "unique" doses of ketamine in IVs, sprays or pills. And desperate patients are shelling out thousands of dollars for treatment often not covered by health insurance, with scant evidence on long-term benefits and risks.

Chicago preschool teacher Lauren Pestikas long struggled with depression and anxiety and several suicide attempts before trying ketamine earlier this year. The price tag is about $ 3,000, but "it's worth every dollar and penny," said the 36-year-old.

Ketamine has received approval from the US Food and Drug Administration for the treatment of depression, although doctors can use it for that purpose. Ketamine has been around since the 1960s and is widely used as an anesthesia drug during surgery because it does not suppress breathing.

Compared to opioids such as morphine, ketamine is not as addictive and does not cause breathing problems. And some studies have shown that ketamine can ease symptoms within hours for the toughest cases.

Ketamine's potential for almost immediate if temporary relief is what makes it so exciting. When delivered through an IV, ketamine can cause a rapid increase in heart rate and blood pressure that could be dangerous for some patients.

Ketamine also can cause hallucinations that some patients find scary. Khare became intrigued and earlier this year began offering ketamine for severe depression at an outpatient clinic. He also joined the American Society for Ketamine Physicians, formed a year ago representing about 140 US doctors, nurses, psychologists and others using ketamine for depression or other nonapproved uses.

There are about 150 US ketamine clinics, compared with about 20 three years ago, said society co-founder Dr. Megan Oxley. Typical treatment at his clinic involves six 45-minute sessions over about two weeks, costing $ 550 each.

About half of that, covering Khare's office visit cost. Patients can receive "booster" treatments. They must sign a four-page consent form that says benefits may not be long-lasting, lists potential side effects, and in bold letters that the treatment is not government-approved treatment is not government-approved

A small Stanford University study published in August suggested that ketamine may help relief by activating the brain's opioid receptors. Relief depression by activating the brain opioid receptors.

Janssen Pharmaceuticals and Allergan are among drug companies developing ketamine-like drugs for depression. Janssen leads the effort with its nasal sprayketamine. The company filed a new drug application.

Meanwhile, dozens of studies are underway seeking to answer some of the unknowns about ketamine including if repeat IV treatments work better for depression and if there is a way to zero in which patients are most likely to benefit.

Depression Treatment

Until there are answers, Zarate of the mental health institute said ketamine should be a last-resort treatment for depression after other methods have failed.