Infusions of ketamine had a beneficial effect on patients who were not responding to more orthodox treatments.
Some were suffering from unremitting depression that had plagued them for years, despite various therapies.
Although many patients in the trial at Oxford Health NHS Foundation Trust relapsed within a day or two, almost 30% showed improvements lasting three weeks.
In 15% of cases, patients took more than two months to relapse and some benefited for eight months. Ketamine, a horse tranquilliser, has become a popular drug on the dance club scene.
It is due to be upgraded from Class C to B amid concern over its physical and psychological effects.