Dear Dr. Levister: For more than five years, I’ve taken a daily low dose aspirin to prevent a heart attack. I understand this is no longer recommended. Have the rules changed? G.D. 

Dear G.D.: Is an aspirin a day the right thing for you? It's not as easy a decision as it sounds. Daily aspirin therapy may lower your risk of heart attack, but daily aspirin therapy isn't for everyone. 

You should take a daily aspirin only if your doctor advises you to do so. If you have had a heart attack or stroke, your doctor will likely recommend you take a daily aspirin unless you have a serious allergy or history of bleeding. If you have a high risk of having a first heart attack, your doctor might recommend aspirin after weighing the risks and benefits. You shouldn't start daily aspirin therapy on your own. 

Although taking an occasional aspirin or two is safe for most adults to use for headaches, body aches or fever, daily use of aspirin can have serious side effects, including internal bleeding. 

Aspirin interferes with your blood's clotting action. When you bleed, your b l o o d ' s clotting cells, called platelets, build up at the site of your wound. The platelets help form a plug that seals the opening in your blood vessel to stop bleeding. 

But this clotting can also happen within the vessels that supply your heart with blood. If your blood vessels are already narrowed from atherosclerosis — the buildup of fatty deposits in your arteries — a fatty deposit in your vessel lining can burst. Then, a blood clot can quickly form and block the artery. This prevents blood flow to the heart and causes a heart attack. Aspirin therapy reduces the clumping action of platelets — possibly preventing a heart attack. 

Although aspirin has been recommended in the past for certain groups of people without a history of heart attack, there's some disagreement among doctors about this approach. Guidelines are changing and have varied between organizations. The bottom line is that before taking a daily aspirin you should have a discussion with your doctor.