Like many drugs, aspirin can provoke a serious, potentially life-threatening allergic reaction. Immediately seek medical attention in the event that you develop hives or rashes; if your throat, mouth, or face swell up; or if your breathing becomes labored. Should you experience any of the following serious side effects, immediately call your physician and do not take any more of this drug: ringing in the ears or other hearing disturbances; excessively dark or bloody feces; pain or inflammation longer than 10 days; fever over three days; coughed-up blood; abdominal pain, intense nausea, or vomiting, especially if the vomit resembles coffee grounds or appears bloody. Most people can take aspirin without experiencing the severe effects. Milder side effects are sleepiness, headache, or heartburn.