Nitrous oxide (N20), better known as laughing gas, is a gas that is inhaled. It is colorless, odorless and is not a known irritant. It is administered through a nose piece and it works very quickly . As such, it is helpful in numbing the nerves in the mouth so that the dentist can work without you experiencing any pain.
There are no known contraindications, or side effects, with the use of nitrous oxide. It is not however, safe to use during the first trimester of pregnancy.