What should I do if I took aspirin after possible concussion?

Aspirin and trauma. Aspirin is counterindicated following trauma such as a concussion because it can slow down clotting and promote bleeding. That being said, the increased risk is pretty small. I wouldn't take more aspirin, but you don't need to do anything about the Aspirin you already took. If you lost conciousness during the head injury or develop new symptoms you should consult your physician.