An experimental drug has been found to lift depression in just over an hour in people who haven't responded to other treatments.
The findings open up the prospect of developing a new fast-working type of anti-depressant.
In a new study, a third of participants responded to the treatment within one hour and 20 minutes, seeing at least a 50 per cent reduction in their symptoms compared to a 15 per cent reduction in those who took a placebo.
Living in a fog: Sufferers of depression report feeling emotionally numb
This was significant as these patients had failed to improve in seven past antidepressant trials.
However, while their were minimal side-effects the dramatic improvements were short-lived with patients finding relief for an average of just half an hour.
The current range of treatments work through the brain's serotonin system, building up levels of this 'happy' hormone over a period of weeks. This can cause great distress to severely depressed patients as many are at high risk of suicide.
However, the latest drug called AZD6765, acts by preventing the binding of a brain chemical called glutamate to nerve cells.
It acts in a similar way to the Class C drug ketamine, but without the serious side-effects such as hallucinations.
Drug pioneer: Dr Carlos Zarate, who has also studied anti-depressive effects of ketamine
Scientists at the National Institutes of Health, who conducted the study, said this could be because the new drug doesn't block glutamate binding as completely as ketamine.
In the trial half of the 22 patients received the drug through an IV drip, while the other half took a placebo. All of them completed a survey assessing their depressive state immediately after taking the drug and a few days after treatment. The two groups then switched the agent they took and went through the same assessment.
The patients reported only minor side effects, such as dizziness and nausea, when taking AZD6765, which were not significantly different from those experienced with the placebo.
Research leader Dr Carlos Zarate, said: 'Our findings serve as a proof of concept that we can tap into an important component of the glutamate pathway to develop a new generation of safe, rapid-acting practical treatments for depression.'
The team reported their results online in the journal Biological Psychiatry. They now want to do further trials, testing whether repeated infusions a few times per week or higher doses might produce longer-lasting results.
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