As U.S. 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.

With limited research on its effectiveness against pain, some experts worry the U.S. may be repeating mistakes that gave rise to the opioid crisis: overprescribing a questionable drug that carries significant safety and abuse risks.