In America and Europe, a growing number of clinics are offering ketamine to treat depression. The anaesthetic—also used illegally as a party drug—can provide rapid relief from the condition where traditional treatments, such as antidepressant drugs, have failed. We investigate how the therapy works, and ask what role it will play in the future of mental-health care. And, as ketamine treatments spread, is enough known about the drug’s long-term safety? Alok Jha hosts with Natasha Loder, The Economist’s health policy editor. For full access to The Economist’s print, digital and audio editions subscribe at economist.com/podcastoffer and sign up for our weekly science newsletter at economist.com/simplyscience. See acast.com/privacy for privacy and opt-out information.