From other information I've read (via Rose), the study prohibited those who've been suicidal or have psychosis episodes. Which does suggest the patients concerned were on the more 'moderate' side of moderate to severe. And the group studied was very small. So I do question the validity of the study.

On a more personal level, having experienced a ketamine infusion for pain, and how horrendous that was in terms of hallucinations and the impact that had on me, I would not take this option in a million years!