WASHINGTON, D.C.: As US doctors scale back their use of opioid painkillers, a new option for hard-to-treat pain is taking root: ketamine, the decades-old surgical drug that is now a trendy psychedelic therapy.

Prescriptions for ketamine have soared in recent years, driven by for-profit clinics and telehealth services offering the medication as a treatment for pain, depression, anxiety and other conditions. The generic drug can be purchased cheaply and prescribed by most physicians and some nurses, regardless of their training.