IMHO, it was the easy way out. You do a trial with one substance at a time, and do a simple randomized controlled trial; which is how most of medical research

IMHO, it was the easy way out. You do a trial with one substance at a time, and do a simple randomized controlled trial; which is how most of medical research works. More than one agent and you have to hire more statisticians to do your experimental design, and it is harder to get somewhat simpleminded grant committees to understand your proposal.