You can, but the timing is critical. If you take ibuprofen first, it fills up the same molecular site inside platelets that aspirin binds to. If ibuprofen is already there, the aspirin can’t bind, which means aspirin’s potent anti-clotting action can’t get started.
To get around this, you can take low-dose aspirin, typically 81 milligrams, in the morning, then wait an hour or two before taking ibuprofen for pain. In the evening, take your last ibuprofen dose, then wait 8 hours before taking aspirin.
At the molecular level, “the interaction of aspirin and ibuprofen is a clash of the titans which has potentially very serious consequences,” said Dr. Christopher P. Cannon [cq], a cardiologist at Brigham and Women’s Hospital. “It has flown under the radar screen of a lot of people, yet it is pretty important information.”
In a little-noticed statement last fall, the US Food and Drug Administration warned about the concomitant use of aspirin and ibuprofen (drugs like Motrin or Advil), citing studies of the way the two drugs compete for virtually the same molecular site.
The key concept, said Dr. Nauder Faraday [cq], an associate professor of anesthesiology and critical care medicine at Johns Hopkins University, is that when aspirin gets into a platelet, that binding is permanent – for the life of that platelet, typically about a week. Put differently, once aspirin is inside a platelet, an enzyme called COX-1 is permanently blocked, effectively stopping the chemical chain of events that leads to blood clotting. Because new platelets are constantly being made, you have to take low-dose aspirin every day to keep damping down the clotting process.
Ibuprofen, while effective for pain, is not a good drug at protecting against heart attacks. When it binds to the site inside platelets, it falls off in a few hours, so the anti-clotting effect is temporary.