Washington, Dec 10 (IANS): Used as an anesthetic in medicine and dentistry, nitrous oxide, or laughing gas, may also help treat severe depression in patients whose symptoms do not respond to standard therapies, finds a research.

"We believe therapy with nitrous oxide eventually could help many people with depression," said principal investigator Peter Nagele, assistant professor of anesthesiology at Washington University School of Medicine in St. Louis.

The pilot study is believed to be the first research in which patients with depression were given laughing gas.

In 20 patients, who had treatment-resistant clinical depression, the researchers found two-thirds experienced an improvement in symptoms after receiving nitrous oxide.

Although the researchers evaluated the effects of the treatment only twice over a 24-hour period, they found the results encouraging.

Laughing gas is attractive because its side effects are limited and the most common are nausea and vomiting. It also leaves the body very quickly after people stop breathing the gas.

That is why researchers believe the improvement in symptoms a day later is real and not a side effect of the nitrous oxide.

"It is kind of surprising that no one ever thought about using a drug that makes people laugh as a treatment for patients whose main symptom is that they are so very sad," Nagele said.

The study appeared online in the journal Biological Psychiatry.