The drug — which Twitter boss Elon Musk reportedly microdoses to treat the condition — benefited treatment-resistant adults, Australian researchers found.

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They tested it on 179 patients who had no success with antidepressants or talk therapy, with some given a placebo.

Professor Colleen Loo, of the University of New South Wales, said: “For people with treatment-resistant depression, 20 per cent remission is actually quite good.

“We found ketamine was clearly better than the placebo — with 20 per cent reporting they no longer had clinical depression compared with only 2 per cent in the placebo group. 

“This is a huge and very obvious difference and brings definitive evidence to the field which only had past smaller trials.”

Around one in six Brits — 16 per cent of adults — suffered moderate to severe depression symptoms in 2022, according to the Office for National Statistics.

Previous studies have shown ketamine, a horse tranquilliser that is illegal for human use in Britain, can help treat the condition.

Musk last year tweeted: “I’ve talked to many more people who were helped by psychedelics & ketamine than SSRIs and amphetamines.”

It cannot be prescribed on the NHS and the National Institute for Care and Excellence (NICE) last year rejected a ketamine nasal spray for medical use.

Trials have shown that it is as effective for severe depression as electroconvulsive therapy, which is normally considered the “gold standard” treatment, however.

The latest study, published in the British Journal of Psychiatry, looked at how well the drug performs compared to a placebo.

Participants were either given bi-weekly injection of the drug or a placebo that causes similar “woozy” effects.

After a month, around a third given ketamine said their symptoms had improved by at least 50 per cent.

In a fifth of cases patients’ symptoms completely disappeared, compared to just two per cent of those given the placebo.