Nitrous oxide (N 2 O; laughing gas) is clinically used as a safe anesthetic (dentistry, ambulance, childbirth) and appreciated for its anti-anxiety effect. Since five years, recreational use of N 2 O is rapidly increasing especially in the dance and festival scene. In the UK, N 2 O is the second most popular recreational drug after cannabis. In most countries, nitrous oxide is a legal drug that is widely available and cheap. Last month prevalence of use among clubbers and ravers ranges between 40 and almost 80 percent. Following one inhalation, mostly from a balloon, a euphoric, pleasant, joyful, empathogenic and sometimes hallucinogenic effect is rapidly induced (within 10 s) and disappears within some minutes. Recreational N 2 O use is generally moderate with most users taking less than 10 balloons of N 2 O per episode and about 80% of the users having less than 10 episodes per year. Side effects of N 2 O include transient dizziness, dissociation, disorientation, loss of balance, impaired memory and cognition, and weakness in the legs. When intoxicated accidents like tripping and falling may occur. Some fatal accidents have been reported due to due to asphyxia (hypoxia). Heavy or sustained use of N 2 O inactivates vitamin B 12 , resulting in a functional vitamin B 12 deficiency and initially causing numbness in fingers, which may further progress to peripheral neuropathy and megaloblastic anemia. N 2 O use does not seem to result in dependence. Considering the generally modest use of N 2 O and its relative safety, it is not necessary to take legal measures. However, (potential) users should be informed about the risk of vitamin B 12 -deficiency related neurological and hematological effects associated with heavy use.