Pretty much all the non-steroidal anti-inflammatory drugs (NSAIDs) except acetaminophen (Tylenol) will interfere with clotting mechanisms and hence increase the amount of menstrual bleeding. It may be a small change or a big one, but most women do notice an increase. This is annoying, because most women also find that NSAIDs other than Tylenol do a far better job at controlling the discomfort associated with menstrual cramps (due to the majority of NSAIDs decreasing prostaglandin production, which typically peak at the time of menstruation and are thought to increase the uterine muscle contractions (cramping) that causes menses to be uncomfortable).