Headache pills

[philandlil]

If on the list of side effects headache is listed how did the people testing it know that it wasn't the same headache they had in the first place?

[gen2]

Simple.  You give the pills to someone who doesn't have a headache.  If they then get a headache it is either a coincidence or a side effect, so you repeat the experiment with many more victims (aka volunteers).

[dilligaf]

Thought about your question but it just gave me a headache.