You just need a similarly bitter placebo. Make (sugar+caffeine) and (sugar+quinine)* such that you can’t tell the difference and ask a friend put to them in two bottles labeled with “A” and “B”.
(*: Quinine is probably a bad choice for a placebo, since it has its own effects that might confuse the results. It’s just the first thing that came to mind that’s bitter.)
You just need a similarly bitter placebo. Make (sugar+caffeine) and (sugar+quinine)* such that you can’t tell the difference and ask a friend put to them in two bottles labeled with “A” and “B”.
(*: Quinine is probably a bad choice for a placebo, since it has its own effects that might confuse the results. It’s just the first thing that came to mind that’s bitter.)