A drug derived from ketamine which can treat depression within days is set to be available in the UK before the year is out.
Esketamine, one of the two mirror image molecules making up ketamine, is already available in the United States in IV form and in March the Food and Drug Administration (FDA) approved it as a nasal spray.
The drug will be considered by European and UK regulatory health agencies in November and next March the National Institute for Health and Care Excellence is expected to announce a decision on its use.
It will be available in private clinics initially, and a cost negotiation will have to take place before it is rolled out on the NHS, experts say.
Previous trials have shown patients whose depression has not responded to traditional antidepressants improve rapidly, some within hours and days.
Traditional antidepressants usually take a number of weeks before patients experience a change.
Professor Allan Young, speaking at the Science Media Centre, said that there have been few changes in the drugs used to treat depression over the past 50-60 years, adding: "People say that we are still in the age of steam and we need to go to the next technological advance and I think that's true."
He continued: "What's exciting is the arrival of a new type of drug, which is ketamine.
"What's new about this is that it's got a different pharmacology, so it's not the same old steam engine, it seems to work in a different way and also it seems to work more quickly.
"We know that classic antidepressants, and actually other treatments, take a fairly prolonged period of time to work, if you can actually get things better much more quickly that's a good thing."
Dr Carlos Zarate, a US co-inventor of a patent for using ketamine to treat depression, said side effects include decreased awareness of the immediate environment, vivid dreams, trouble communicating and disassociation.
But because of the low doses used, compared to recreational use, "people maintain insight, understand what's going on", he said.
He said the results from previous trials were "remarkable" and said scientists can build on it "to develop better treatments that don't have the side effects or abuse potential of ketamine".
Dr Rupert McShane, who runs an NHS self-pay ketamine clinic in Oxford, said "there is a lot of interest, it's escalating".
But he said access to esketamine may take a while because it will involve a large amount of time in clinics.
Patients must spend two hours in the clinic as the side-effects wear off with doses expected twice a week for the first month of treatment.
He is calling for an independent multi-drug registry where patients will log each ketamine or esketamine treatment through an app to track usage.
He said: "It's a drug, not a miracle, in my experience. But, ketamine is, in my experience, and esketamine according to the data, is a potent and sometimes transformative antidepressant. The risks appear low at one year in the trial populations of esketamine, but the potential for harm with long-term clinical use is simply unknown, and that's why registry is really needed."
He added: "We need to think about protecting the drug from inappropriate use."