Injecting someone with another psychoactive drug would not be a placebo. We would be comparing the efficacy of {other psychoactive drug} and ketamine. That's not to say this experiment has no value, it's one of the many experiments we should run to help build the case for ketamine.

The classic gold standard is to randomly assign subjects to groups. Then give one group a sugar pill, give the other group the treatment pill. Neither to patient, the person administering, or the person recording the results know who got the treatment who got the placebo. This is not possible with ketamine, psilocybin, MDMA, LSD, etc. That's fine, we can still build a strong body of experimental evidence of their efficacy. It bothers me when clearly non-blind non-mask experiments are labeled as double-blinded, which we see often in this body of research, this study included.

There is precedent for this; it's called "active placebo." For example, I think some of the psilocybin trials used methylphenidate as an active placebo comparison condition.

Sure, but as a scientist conducting an experiment I will be able to determine who is dosed with psilocybin and who is doses with methylphenidate >90% of the time, thus removing the observer mask. I think the average patient would be able to tell if they were dosed with psilocybin or methylphenidate, even if they were drug naive, thus removing the patient mask.

I'm not saying it's impossible to conduct good experiments on these substances. I'm saying that they require special considerations of internal validity and it's incorrect to call this study (iv ketamine vs iv saline water) double blind.

The person assessing the depression response in the psilocybin studies is not in the room with the person while they are under the influence of the substance. The ratings are done on a different day. It's two different people to preserve blinding.