In 2015 and 2016, during the debates that culminated in The Psychoactive Substances Act 2016, both houses of the UK parliament debated the pharmacology of nitric oxide and amyl nitrites, otherwise known as “poppers”. The original draft Psychoactive Substances Bill had recommended that poppers should be made illegal. However, after strong opposition inside the Conservative party, the ruling party at the time, the government found a way to not ban them by claiming they were not psychoactive. Nitrous oxide, another recreational gas, was also a possible target of the Psychoactive Substances Bill but this was never explicitly mentioned in the debates. Once the Psychoactive Substances Act came into force the Crown Prosecution Service stated that nitrous oxide was psychoactive and so illegal to sell for psychoactive purposes. Many sellers of nitrous oxide canisters were arrested and some sent to prison. A series of Crown court prosecutions for nitrous oxide possession followed in which the Crown claim that nitrous oxide was psychoactive was challenged. In some of these the defendant was acquitted so making its current legal status uncertain . Here we delve into the pharmacology of nitric oxide and nitrous oxide and how the effects of these two gasses are related. A clear understanding of the pharmacology of these gasses is essential for the scientific underpinning of legislation which will directly impact on the life of recreational users and people involved in the selling of these substances.