A fast acting ketamine-like anti-depressant spray that can lift mood within hours has been rejected by the NHS healthcare watchdog.
The National Institute for Health and Care and Excellence (NICE) says there are too many uncertainties about the correlation between the price and clinical benefits of esketamine.
It is licensed as a therapy for people with hard-to-treat depression.
But it costs about £10,000 per patient for a single course of treatment.
Some people already prescribed it - as part of a trial, for example - will be able to continue on the treatment if their doctor says it is appropriate to do so, the NICE's draft recommendation for England and Wales says. Scotland is yet to issue guidance.
Experts have expressed mixed reactions to NICE's decision.
Dr Sameer Jauhar, at the Institute of Psychiatry, Psychology and Neuroscience, King's College London, said NICE had made the call because there was not yet enough long-term evidence to support the use of nasal esketamine alongside another anti-depressant.
Consultant psychiatrist Dr Paul Keedwell, at Cardiff University, said patients would be disappointed by a decision based largely on cost rather than lack of effectiveness.
Marjorie Wallace, chief executive of mental health charity Sane, said: "People with depression are currently relying on medications that are 30 years old.
"Although these drugs can be life-saving for some people, they can have unpleasant side-effects and do not work for everyone.
"It is therefore deeply disappointing that the first new compound that works in a fundamentally different way on the brain should not have passed this hurdle.
"This is especially so because people can take as much as six to eight weeks to feel the full effects of most anti-depressants.
"We hope this setback will serve only to inspire pharmaceutical companies, researchers and others to discover new ways of treating serious depression."
Ketamine is used in medicine to numb the body or induce sleep and sometimes prescribed for depression.
But the drug also has a reputation for recreational misuse.
Esketamine, also called Spravato and made by Janssen, is a form of ketamine that targets glutamate, a chemical linked with learning and memory.
The spray is absorbed through the nose into the blood stream.
The draft guidance from NICE is open for consultation until 18 February 2020.
Janssen said it was deeply disappointed about the draft decision but still hoped to ensure patients could access esketamine in the future.