Some people find that taking aspirin upsets their stomach. To avoid this side effect, patients should take aspirin with meals, or a full glass of water or milk. Buffered aspirin, which is coated with an antacid, may help prevent this side effect. Symptoms associated with upset stomach from aspirin may include stomach pain and vomiting.

In some cases, patients who take aspirin experience serious gastrointestinal disorders such as ulceration of the stomach lining or bleeding of the gastrointestinal tract or urinary tract. High doses of aspirin have been known to cause hearing loss, which is usually preceded by a ringing sound in the ears known as tinnitus.

Aspirin can also trigger blood problems such as decreased counts of white blood cells and platelets, and hemolytic anemia (inadequate number of circulating red blood cells caused by premature destruction of these cells). In addition, people who take aspirin are at risk for increased bleeding. For example, patients with cuts or nosebleeds may find that they bleed longer than they otherwise would. In most instances, this is not a serious problem. However, in some patients it can lead to increased bleeding of ulcers or, rarely, bleeding in the brain (hemorrhagic stroke).

The National Institutes of Health (NIH) cautions about two forms of kidney disease that can result from use of over-the-counter pain drugs including aspirin:

• Sudden-onset acute kidney failure can occur in people with risk factors including old age, chronic kidney disease, systemic lupus erythematosus or alcohol abuse.
  
  
• Chronic kidney damage (analgesic nephropathy) can develop in anyone taking these drugs daily over several years. This risk increases when combining two or more analgesics (especially aspirin and acetaminophen together) with caffeine or the opioid codeine.

Some patients have an allergic reaction to aspirin. This may cause a person’s face to swell, a condition known as angioedema. In some cases, this allergy can bring on an asthma attack.

Patients who experience any of the following more substantial side effects should contact their physician immediately:

• Ringing in the ears, ear pain or loss of hearing
• Bloody or black stools
• Wheezing or other breathing difficulties
• Dizziness
• Mental confusion
• Drowsiness
• Skin rash