Most women likely have figured this out on their own, if the reaction to this study in a recent meeting was any indication, but we like data, so here you go...
Researchers at the Cochrane Library have analyzed studies (because that's what they do -- and they do it well) on pain relief for dysmenorrhoea, known by most people as menstrual cramps. They concluded that non-steroidal anti-inflammatory drugs seem to be more effective at controlling such pain than paracetamol, known my most North Americans as acetaminophen.
Here's the abstract of the study (go to the bottom of the page for the "plain language summary").
As for which NSAID was more effective or safer, the researchers couldn't say. Other over-the-counter NSAIDs include naproxen (Aleve) and aspirin.
Here's more on menstrual cramps and pain relief from MedicineNet. It explains why aspirin might not be the best choice either. The old standby has less effect on chemicals called prostaglandins.
-- Tami Dennis