Laughing Gas Illustration (IMAGE) Washington University School of Medicine Caption Nitrous oxide (laughing gas) has been used as an anesthetic in medicine and dentistry for 150 years. In this illustration from a 19th century book, a man is shown dancing after inhaling the gas. Now, researchers at Washington University School of Medicine in St. Louis are evaluating nitrous oxide as a treatment for depression. Credit Wellcome Library, London. Wellcome Images Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.