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.