As detailed in the WSJ here, regarding that recommendation that everyone of a certain age take a little aspirin every day:

Public-health officials are scaling back official recommendations for the painkiller to target a narrower group of patients who are at risk of a heart attack or stroke.

They’re worried about side effects, such as ulcers. As the UK Netdoctor says,

The second most common cause [of peptic ulcers] is damage inflicted by aspirin (eg Disprin) or non-steroidal anti-inflammatory drugs (NSAIDs, such as diclofenac (eg Voltarol) or naproxen (eg Synflex)) used by many for arthritis, rheumatism, backache, headaches and period pain.

It’s always something.