Nitrous oxide, also known as laughing gas, is most often used for patients who are mildly or moderately anxious or nervous. It eases their fears so that they can relax and receive treatment comfortably and safely. Nitrous oxide is administered by placing a small mask over the patient's nose. As the gas begins to work, the patient becomes calm, although he or she is still awake and can talk. When the gas is turned off, the effects of sedation wear off almost immediately.