Nitrous oxide, also known as laughing gas, has shown promise as a treatment for depression. When people inhaled a low dose as part of a small study, their depression improved over the next two weeks.
It has long been known that nitrous oxide can give a short boost to mood as well as relieving pain – hence its original name of laughing gas – but the effect is thought to wear off quickly. Nitrous oxide is one of the most common anaesthetics, used by hospitals, dental surgeries and paramedics, as well as being available illegally in small capsules for recreational use.
The gas seems to chiefly affect the brain by blocking molecules on nerve cells called N-methyl-D-aspartate (NMDA) receptors. This is the same thing targeted by the stronger anaesthetic ketamine, which also relieves depression; a similar chemical to ketamine has recently been approved as a new intranasal spray treatment.

It isn’t known how NMDA receptors change mood. But as the antidepressant effects of ketamine started to emerge, Peter Nagele, then an anaesthetist at Washington University School of Medicine in St Louis, Missouri, wondered if nitrous oxide had similar potential.
In 2014, he and his colleagues found that one hour’s inhalation of nitrous oxide reduced symptoms for up to a day in people with depression who hadn’t improved after trying standard antidepressant medicines, but the study didn’t record whether the effect lasted any longer.

Read more: www.newscientist.com/article/2280399-laughing-gas-has-shown-...