> there may have only been one patient out of millions who had a seizure while 50% experienced headache, yet the handout probably won't tell you that.

Odd, here in Norway that's exactly the kind of information I expect to see on a leaflet inside the packet, not only on prescription drugs but also over the counter pain killers like paracetamol. Roughly translated from the Norwegian it says:

Rare side effects (more than one in ten thousand but fewer than one in one thousand patients) include: over sensitivity, allergic skin reaction/rash, reduced white blood count, anaemia, disturbed liver function. Very rare side effects include serious skin reactions. Liver function can be affected by paracetamol and alcohol abuse.