Nitrous oxide. Or laughing gas is a drug that can decrease awareness and pain. It must be administered by someone trained in its use and proper monitoring should be utilized (a pulse oximeter at a minimum). When this drug is used, essentially you are being "put under".
Decreases anxiety. Nitrous oxide is used with a normal oxygen level so a patient is not put "under" it server to lessen anxiety for nervous patients. For long procedures or in higher doses it can cause vomiting or stomach upset. Local injection anesthesia is still needed when using nitrous oxidev gas.