If you're trying to buff up without (technically) cheating, all you may have to do is take a hit of the recommended daily dose of ibuprofen (the main ingredient of Advil) or acetaminophen (the main ingredient in Tylenol), according to a presentation by Chad Carroll at the American Physiological Society. For three months, Carroll and his team at the Human Performance Laboratory in Ball State University stuck 36 men and women in a gym three times a week for 15–20 minute weight sessions, giving them either a placebo or the recommended daily dosage of ibuprofen or acetaminophen every day.The group that took a placebo got bigger, stronger muscles—but those rolling on ibuprofen or acetaminophen did even better, as measured by MRI. The drugs work by blocking an enzyme called cyclooxygenase, commonly referred to as COX. Dr. Trappe thinks that, over time, this action enhances the muscle's metabolic response to resistance exercise, allowing the body to build substantially more muscle. However, a previous study by the same authors found that over a 24-hour period, ibuprofen and acetaminophen actually had a negative impact on muscle protein synthesis. But there might be another possibility: Painkillers help you build more muscle because they kill the pain that comes with working out. When a person is following a weight-lifting regimen, he'll often be sore the day after a work-out, with the effects ranging from taking the elevator instead of the stairs to relative immobilization. But if the same person chomped down on painkillers every day, they'd not only be able to work out harder, but they'd feel better and healthier outside the gym as well, and likely use their muscles more in those situations. So the increase in muscle mass may have little to do with the effect of chemical properties of ibuprofen and acetaminophen on muscle synthesis, and more with the ability to work out without getting sore. This is, in fact, how many illegal performance enhancing drugs work—they cause muscles to heal faster, allowing athletes to work out harder and longer, and thus build substantially more muscle. They often do not have a direct muscle-building effect.