NO2 was a 'recreational drug' well before its therapuetic effects were recognised; http://tinyurl.com/84q2jl - has a wonderful 'Cruikshank' drawing of a 'laughing gas party' c1840, which might well be a Club in Anytown this weekend at 2am. The spoilsports at the (UK) 'Medicines and Health-care products Regulatory Agency' point out that supplying nitrous oxide for non-medical inhalation is an offence - but you can legally buy it for making foamed cream for catering purposes...