Researchers in the US have identified new drug compounds that could successfully treat depression in less than 24 hours, while minimising side effects.

Although they have not yet been tested in people, the compounds could offer significant advantages over current antidepressant medications.

“[The] results open up a whole new class of potential antidepressant medications,” said lead researcher Dr Scott Thompson from the University of Maryland.

“We have evidence that these compounds can relieve the devastating symptoms of depression in less than one day, and can do so in a way that limits some of the key disadvantages of current approaches.”

Currently, most people with depression take medications that increase levels of the neurochemical serotonin in the brain.

The most common of these drugs, Prozac, is a 'selective serotonin reuptake inhibitor' (SSRI).

Unfortunately, SSRIs are effective in only a third of patients with depression. In addition, even when these drugs work, they typically take between three and eight weeks to relieve symptoms and can come with some serious side effects.

As a result, patients often suffer for months before finding a medicine that makes them feel better. This is not only emotionally excruciating; in the case of patients who are suicidal, it can be deadly.

Dr Thompson and his team focused instead on another neurotransmitter - an inhibitory compound called GABA.

Brain activity is determined by a balance of opposing excitatory and inhibitory communication between brain cells, and many argue that in depression, excitatory messages in some brain regions are not strong enough.

Because there is no safe way to directly strengthen excitatory communication, Dr Thompson and his team examined a class of compounds that reduce the inhibitory messages sent via GABA. They predicted that these compounds would restore excitatory strength.

These compounds, called GABA-NAMs, appear to minimise unwanted side effects because they are precise; they work only in the parts of the brain that are essential for mood.

The researchers tested the compounds in rats that were subjected to chronic mild stress that caused the animals to act in ways that resemble human depression.

Giving stressed rats GABA-NAMs successfully reversed experimental signs of a key symptom of depression, anhedonia, or the inability to feel pleasure.

Remarkably, the beneficial effects of the compounds appeared within 24 hours – much faster than the multiple weeks needed for SSRIs to produce the same effects.

“These compounds produced the most dramatic effects in animal studies that we could have hoped for,” Dr. Thompson said.

“It will now be tremendously exciting to find out whether they produce similar effects in depressed patients. If these compounds can quickly provide relief of the symptoms of human depression, such as suicidal thinking, it could revolutionize the way patients are treated.”

In the tests on rats, the researchers found that the compounds rapidly increased the strength of excitatory communication in regions that were weakened by stress and are thought to be weakened in human depression.

No effects of the compound were detected in unstressed animals, raising hopes that they will not produce side effects in human patients.