When you pop an aspirin, you're taking the world's most widely used medication, according to a study in the journal Vascular Pharmacology. It's been a favorite for 3,500 years — ever since Sumerians and Egyptians used willow bark (it has aspirin's active ingredient in it) to treat pain and fevers.

But it’s important that it be taken correctly. Too much can cause risky bleeding and gastrointestinal distress, and too little may not be enough to avoid a blood clot, heart attack, or stroke.

A study in JAMA shows that many people who are on Medicaid or who don't have insurance are taking low-dose aspirin when it offers them no benefit — and comes with risks.

And, ironically, people who have atherosclerotic cardiovascular disease and are rated at a 10% or higher 10-year risk for a dangerous cardiac event are taking low-dose aspirin less frequently than they should to reduce their risk.

Who should take low-dose aspirin regularly?

It's an individual decision, but generally it's recommended for people who have had or are at great risk for a heart attack or stroke — not for primary prevention of cardiovascular disease.

But if you're age 40 to 79, your doctor can use an Atherosclerotic Cardiovascular Disease Risk Calculator to determine if aspirin will benefit you. The calculator evaluates your age, sex, blood pressure, cholesterol, and high-sensitivity C-reactive protein levels, as well as considering whether your mother or father had a heart attack before age 60 — and then ranks your risk level.