That nitrous oxide shows some efficacy in “treatment-resistant” depression is not a big surprise, nor is it a particularly welcome one.  Several points:

1. “Treatment-resistant depression” merely means depressions that have been inadequately treated.  Most “depression pills,” Prozac and its cousins, would fall into the category of inadequate treatments, because they simply are not very effective in real depression —  aside from the combination of unhappiness, dysphoria, and demoralization that many people have.  None of these qualifies as serious depression.
2.  We already have excellent treatments for serious depression, which actually work and have few side effects.  Electroconvulsive therapy (ECT, or shock therapy) is highly effective and there are not a ton of side effects. The various magnetic stimulations show promise.  Some of the earlier drugs for serious depression have side effects, to be sure — but what is worse, a bit of dry mouth or suicide?  Putting the media spotlight on laughing gas in this manner detracts from psychiatry’s already prolific arsenal of treatments.
3.  Any drug that affects mood or consciousness is probably a potential antidepressant.  Flurothyl (Indoklon), a diethyl ether, really works — as a convulsive agent against serious depression.  Some of the hallucinogens, such psilocybin, are currently being investigated.  Opium is the oldest antidepressant in history and has powerful effects against melancholic (“treatment-resistant”) depression.  Ditto the opium alkaloids, such as morphine.  This list could go on.

Now, I have no doubt that nitrous oxide is promising as well, where the depression pills such as Prozac have failed.    But the point is that plenty of other drugs also work where the depression pills have failed.  Yet if we try to get an overview, rather than just a series of media enthusiasms, patients with “treatment-resistant depression” are numberless.  What we need is a change is in “innovation-resistant” psychiatry, that rears back about prescribing anything not currently being flogged by the drug reps.