We’ve known for a long time that aspirin can help prevent damage from a heart attack or a stroke if taken during one of those events. In fact, you might have seen ads about how aspirin can be lifesaving during a heart attack.

Research backs that up. For people who have already experienced a heart attack or stroke, a daily aspirin regimen can actually prevent future heart attacks and strokes.

But, as helpful as aspirin is to prevent recurrent heart attacks or strokes (this is called secondary prevention), a daily aspirin has long been controversial to prevent a first heart attack or stroke (this is called primary prevention).

To use aspirin for primary prevention, doctors are supposed to assess a patient’s risk of a first heart attack or stroke and decide when benefits of aspirin outweigh risks. But new draft guidelines for aspirin use have created confusion about who, exactly, should actually take aspirin.