Aspirin: what it treats, how to take it, side effects
Last updated September 3, 2026.
Aspirin is a pain reliever, fever reducer, and - at a low daily dose - a blood thinner that helps prevent heart attacks and strokes. It is the oldest drug in the cabinet and still one of the most consequential. It is an NSAID, so it carries the class risks of stomach bleeding.
What does it treat?
MedlinePlus lists four jobs: reducing fever, relieving mild to moderate pain and inflammation, preventing heart attacks, strokes, and mini-strokes, and reducing the risk of death in people having or recovering from a heart attack. Doctors also use it for rheumatic fever, Kawasaki disease, blood clot risk, and certain pregnancy complications. The daily low dose (81 mg, baby aspirin) for heart protection is a doctor decision, not a self-start.
How do you take it?
For heart attack and stroke prevention: once a day, exactly as your doctor directed. For fever or pain: every 4 to 6 hours as needed - the 325 mg label says 1 or 2 tablets every 4 hours with a full glass of water. Swallow extended-release tablets whole; chewable tablets can be chewed, crushed, or swallowed whole with a full glass of water right after. Two stop rules: call your doctor if fever lasts more than 3 days or pain more than 10, or if the painful area becomes red or swollen.
Side effects to know
- Common: nausea, vomiting, stomach pain, and heartburn.
- Serious: bleeding is the signature risk - bloody vomit or vomit that looks like coffee grounds, bright red blood in stools, or black, tarry stools mean calling your doctor immediately. Ringing in the ears or hearing loss signals too much salicylate. Allergic reactions (hives, rash, facial or throat swelling, wheezing, difficulty breathing, hoarseness, fast heartbeat, fast breathing, cold clammy skin) are emergencies.
Who should not take it?
Children and teenagers who have or are recovering from chickenpox or flu-like symptoms should not use it - the label's Reye's syndrome warning. If you have asthma with frequent stuffed or runny nose or nasal polyps, aspirin can trigger an allergic reaction, and your doctor may rule it out entirely. Flag heartburn, ulcers, anemia, bleeding problems like hemophilia, and kidney or liver disease. Pregnancy: doses above 81 mg may harm the fetus and cause delivery problems at or after 20 weeks - do not take 325 mg doses then unless your doctor directs it. If you take daily aspirin for your heart, do not add ibuprofen for pain without asking your doctor; the two interact. Three or more alcoholic drinks a day is another talk-to-your-doctor-first line, and mention aspirin before any surgery, including dental work.
When is it an emergency?
Bloody or coffee-ground vomit and black, tarry stools mean internal bleeding - get immediate care. Facial or throat swelling, wheezing, or trouble breathing is a 911 call. Overdose symptoms - burning throat or stomach pain, vomiting, decreased urination, fever, restlessness, confused rambling speech, fear or nervousness - mean Poison Control at 1-800-222-1222 and emergency services. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Should I take a daily aspirin to protect my heart?
Only if your doctor has weighed in. MedlinePlus lists preventing heart attacks and strokes among aspirin's uses, but the same drug raises bleeding risk, and who benefits is a person-by-person medical judgment. If your clinician prescribed the daily low dose, take it exactly as directed and do not stop without asking.
Why can't kids take aspirin?
Reye's syndrome. The label warns that children and teenagers who have or are recovering from chickenpox or flu-like symptoms should not use aspirin - it can trigger a rare but serious illness. Use acetaminophen or ibuprofen for kids' fevers instead, per their own labels.
Can I take ibuprofen with my daily aspirin?
Not without checking. MedlinePlus says if you take aspirin regularly to prevent heart attack or stroke, do not take ibuprofen for pain or fever without talking to your doctor - your doctor will likely tell you to space the two apart, because ibuprofen can interfere with aspirin's protective effect.
Can I drink alcohol while taking aspirin?
Heavy drinking is a named concern: MedlinePlus says if you drink three or more alcoholic drinks every day, ask your doctor whether you should take aspirin or other pain and fever medications at all. Alcohol and aspirin both irritate the stomach lining, and together they raise bleeding risk.
Is aspirin safe during pregnancy?
Dose decides. MedlinePlus says low-dose aspirin (81 mg) may be taken during pregnancy under a doctor's care, but doses above 81 mg - like a regular 325 mg tablet - may harm the fetus and cause problems with delivery at or after 20 weeks. Do not take the higher doses then unless your doctor tells you to.
What does aspirin overdose look like?
MedlinePlus's symptom list: burning pain in the throat or stomach, vomiting, decreased urination, fever, restlessness and irritability, talking a lot and saying things that do not make sense, and fear or nervousness. Ringing in the ears is an earlier warning sign at lower excess. Poison Control is 1-800-222-1222.