I guess I can't support 'most'. It did happen in two out of three experiments for which I actually had intimate details.
But this is one of those things that will never get a trustworthy citation, and yet is probable (replace "most" with "significantly many" to increase probability according to your own probability measure).
A drug tested today on humans has, with high probability, been shown to be safe, but most importantly, effective, in an animal model - or is already known to be effective and safe in humans for another use.
Note the term "effective". That means that it is known to have a measurable effect. For many drugs, it is therefore probable that the (human) subject receiving the treatment can tell that it isn't placebo.
Specifically, quite a few psychiatric drugs are known to cause obesity, compulsive thoughts and lactation (even in males). Niacin is known to cause flushing (at lower levels, it is not externally visible, but the sensation is still there). Viagra was discovered during an attempt to treat hypertension. I'm sure the subjects could tell it from the placebo. Similarly for Minoxidil.
To actually assess how prevalent this is, you need at least access to notes made during the experiment, or worse - you need to do measurements and stats that weren't made in the first place (and which making may only make the results less promising; which is a problem in for-profit development)
But this is one of those things that will never get a trustworthy citation, and yet is probable (replace "most" with "significantly many" to increase probability according to your own probability measure).
A drug tested today on humans has, with high probability, been shown to be safe, but most importantly, effective, in an animal model - or is already known to be effective and safe in humans for another use.
Note the term "effective". That means that it is known to have a measurable effect. For many drugs, it is therefore probable that the (human) subject receiving the treatment can tell that it isn't placebo.
Specifically, quite a few psychiatric drugs are known to cause obesity, compulsive thoughts and lactation (even in males). Niacin is known to cause flushing (at lower levels, it is not externally visible, but the sensation is still there). Viagra was discovered during an attempt to treat hypertension. I'm sure the subjects could tell it from the placebo. Similarly for Minoxidil.
To actually assess how prevalent this is, you need at least access to notes made during the experiment, or worse - you need to do measurements and stats that weren't made in the first place (and which making may only make the results less promising; which is a problem in for-profit development)