Some discussion of pharma-psychiatry stuff, i haven't gone through to verify claims (whether it's some crank journals), but the gist is that antidepressants show effectiveness around placebo for depression treatment, and thus not getting success from them and getting approved for ketamine shouldn't inspire confidence, as it shows the same effectiveness.
(obviously not a call to abandon medication if it helps you, who it helps - it helps)
Placebo effect can be pretty strong, then. At least that's one way to think of it.