Otherwise known as laughing gas, nitrous oxide – N2O – has been used as an anaesthetic since the 19th century. It is commonly used during childbirth, after trauma and in end-of-life care, usually in a 50-50 mixture with oxygen, sometimes called “gas and air”.
Its use as a recreational drug also has a long history, dating back to “laughing gas parties” held by chemist Humphry Davy in 1799. He described effects including giddiness, flushed cheeks, intense pleasure, and “sublime emotion connected with highly vivid ideas”.
These days, people seeking a high from the gas usually obtain it in small steel cartridges sold to the catering industry for making whipped cream. It is then dispensed into a balloon, which users breathe from until they achieve the desired effect. Supplying nitrous oxide for recreational purposes is illegal in the UK under the Psychoactive Substances Act 2016.
The effects come on very rapidly when the drug is inhaled and subside just as quickly. Its precise actions in the brain aren’t well understood, but many of its effects may result from blocking NMDA receptors, stopping them from being activated by the brain chemical glutamate.
Breathing nitrous oxide from a balloon is usually quite safe, but some users have died after trying other methods to inhale the gas for longer, such as putting a bag over their heads, that result in oxygen deprivation. Inhaling gas directly from a pressurised container is also very dangerous.
Chronic use of nitrous oxide can deplete vitamin B12 reserves in the body, causing damage to the nervous system.
Nitrous oxide is also a potent greenhouse gas and ozone-depleting chemical. Although it is present in the atmosphere at much lower concentrations than carbon dioxide – just 330 parts per billion – it has 300 times the heat-trapping capability. It gets into the atmosphere from soil fertilisers, fuel combustion, industrial emissions and peat circles in the Arctic. A pulse of nitrous oxide released from plants may have hastened the end of the last ice age 14,500 years ago.
Further from home, nitrous oxide may provide a clue for scientists looking for life on Mars.