I'm not in the medical field either, but I remember they used niacin (a form of vitamin B₃) as an active placebo in the Good Friday Experiment[0] in 1962. The niacin doses produced some noticeable physiological effects, but it didn't take long before it became abundantly clear for everyone present who had gotten the psilocybin and who had gotten the niacin.

[0]. https://en.wikipedia.org/wiki/Marsh_Chapel_Experiment