Some patients who have faced incurable depression for decades have had symptoms disappear within hours of taking low doses of the drug.
The small trial on 28 people, reported in the Journal of Psychopharmacology, shows the benefits can last months.
Some responded within six hours of the first infusion of ketamine.
Lead researcher Dr Rupert McShane said: "It really is dramatic for some people, it's the sort of thing really that makes it worth doing psychiatry, it's a really wonderful thing to see.
He added: "[The patients] say 'ah this is how I used to think' and the relatives say 'we've got x back'."
Dr McShane said this included patients who had lived with depression for 20 years.
Edited by seeder, 03 April 2014 - 08:51 PM.