To exclude the placebo effect, some of the participants are given placebo, others are given the test drug in different dosages and ways.
So they know that they might be given the placebo?
I regret to have to state the obvious, but that sort of test does not possibly compare with the real and serious shock of being told, supposedly for real, that one is infected.
At the beginning of the pandemic nobody knew but there were big numbers of (at the time) gay men visiting their doctors with similar symptoms. Who told them they are ill?
Does that mean to suggest that the AIDS epidemic was already around except that nobody had yet noticed it?
If it is rather agreed that a disease has spread since then, the issue that I attempt to define is the extent to which this is a disease of the blood as opposed to a disease of the mind.