Aspirin is a nonsteroidal anti-inflammatory drug (NSAID) used to treat pain and inflammation in the body, to treat fever, to prevent blood clots, and to reduce the risk of strokes and heart attacks.
Aspirin may be used off-label (a use not approved by the Food and Drug Administration, or FDA) to decrease the risk of developing hereditary colorectal cancer (i.e., Lynch syndrome).
8 Types of People Who Shouldn't Take Aspirin
When taken as directed for the intended uses, aspirin is generally considered safe, however, it can increase the risk of bleeding and gastrointestinal problems, and certain people should avoid use of aspirin, such as those who:
- Have a stomach or intestinal ulcer or you had bleeding in the gut because aspirin and other NSAIDs can damage the stomach or intestines
- Have heart disease or ever had a stroke, because aspirin and other NSAIDs can increase the risk of heart attack, heart failure, and stroke
- Have kidney disease, heart failure, or cirrhosis, because aspirin and other NSAIDs can worsen heart failure, kidney disease, and cirrhosis
- Take diuretics (“water pills”), because aspirin and other NSAIDs can cause kidney problems in people taking diuretics or some other medicines to control blood pressure
- Have high blood pressure, because aspirin and other NSAIDs can raise blood pressure
- Have disorders that increase the risk of bleeding
- Have surgery planned, because most people need to stop aspirin and other NSAIDs at least several days to a week before surgery to lower the risk of bleeding
- Are pregnant, because use of aspirin and other NSAIDs during the last 3 months of pregnancy should be avoided
What Are the Side Effects of Aspirin?
Side effects of aspirin include:
- Gastrointestinal ulcers or bleeding
- Abdominal pain
- Upset stomach
- Heartburn
- Nausea
- Vomiting
- Gastritis
- Bleeding
- Rash
- Hives
- Drowsiness
- Headache
- Cramping
- Skin swelling (angioedema)
- Bronchospasm
- Liver toxicity
- Hearing loss
- Kidney damage
- Ringing in the ears (tinnitus)
What Drugs Interact with Aspirin?
Aspirin may interact with other drugs, including:
- Blood thinners, such as warfarin (Jantoven) or heparin
- Diuretics
- Antiplatelet drugs such as clopidogrel
- Other salicylates
- Corticosteroids (such as prednisone)
- Lithium
- Methotrexate
- Antidepressants
- Phenytoin (Dilantin, Phenytek)
- Cyclosporine
- Dichlorphenamide
- Mifepristone
- Ginkgo biloba
Check all prescription and over-the-counter (OTC) labels carefully since many medicines contain pain relievers/fever reducers (including aspirin and other NSAIDs such as ibuprofen, naproxen, and ketorolac).
From 
https://www.rxlist.com/aspirin-drug.htm#medguide
https://www.uptodate.com/contents/nonsteroidal-antiinflammatory-drugs-nsaids-the-basics?search=aspirin&source=search_result&selectedTitle=3~148&usage_type=default&display_rank=2
https://reference.medscape.com/drug/bayer-vazalore-aspirin-343279
https://www.hopkinsmedicine.org/health/wellness-and-prevention/is-taking-aspirin-good-for-your-heart