It is either the most exciting new treatment for depression in years or it is a hallucinogenic club drug that is wrongly being dispensed to desperate patients in a growing number of clinics around the country.

It is called ketamine — or Special K, in street parlance.

While it has been used as an anesthetic for decades, small studies at prestigious medical centers like Yale, Mount Sinai and the National Institute of Mental Health suggest it can relieve depression in many people who are not helped by widely used conventional antidepressants like Prozac or Lexapro.

And the depression seems to melt away within hours, rather than the weeks typically required for a conventional antidepressant.

But some psychiatrists say the drug has not been studied enough to be ready for use outside of clinical trials, and they are alarmed that clinics are springing up to offer ketamine treatments, charging hundreds of dollars for sessions that must be repeated many times.