A breakthrough experimental drug has been found to rapidly relieve symptoms of depression in as little as 80 minutes in patients who haven't responded to other treatments.

Researchers said that results from the latest study open the door for the potential development of newer and faster acting antidepressants.

Researchers found that patients who took the experimental drug, known as AZD6765, showed at least a 50 percent reduction in their depression symptoms after just an hour and 20 minutes, compared to those who took the placebo.

However, researchers said that the effect of the fast-acting antidepressant was short lived and lasted for about 30 minutes on average. They noted that some people continued to feel the benefit up to two days after treatment, though.

Researchers said that the latest results, published in the journal Biological Psychiatry, are promising because the participants in the study had failed to improve in seven past antidepressant trials. Researchers said that nearly half of the patients in the study even failed to respond to powerful electroconvulsive therapy (ECT) or "shock therapy".

The study researcher Dr. Carlos Zarate, of the National Institute of Mental Health, said that fast-acting drugs for major depression are urgently needed. He explained that the current range of antidepressants that work by gauging the brain's serotonin levels typically take several weeks to start working. Researchers said that because these drugs can take several weeks to have an effect, it could jeopardize a depressed person's health, especially if they are at high risk of suicide.

Researchers said that the latest AZD6765 drug acts in similar ways to the Class C drug ketamine, by preventing a brain chemical called glutamate from binding to nerve cells, but without the dangerous side effects such as hallucinations. They explain the lack of harmful side effects could be because AZD6765 doesn't block glutamate binding as completely as ketamine.

The study consisted of 22 patients. Half of the patients received the experimental drug from an IV drip while the other half were administered a placebo. Researchers said that all participants were asked to complete a survey assessing their depression immediately after taking the drug and a few days after treatment.

Researchers then switched the groups and participants went through the same assessment as in the first half of the experiment.

The patients reported only minor side effects like dizziness and nausea, when taking AZD6765. Researchers noted that the side effects were not significantly different from those experienced with the placebo.

"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," Zarate said in a statement.

Zarate and his team now want to test whether repeated infusions a few times per week or administering higher doses might produce longer-lasting results.