What effect would one baby aspirin have if you take it while you have a high blood pressure, eg 180/100?

Too high: Your BP is not under controll. Get further medicines adjusted for better BP control.

Most likely it's ok: Most likely nothing will happen. Theoretically, there is a very small risk if one were to have a stroke or tear in the great vessel of the body(aortic dissection) Aspirin could make things worse by causing bleeding, but this risk is extremely low.

Platelets inhibited: Low dose Aspirin inhibits blood platelet function and can be associated with bleeding. The high blood press ure requires evaluation and treatment. You should see a doctor for this.

Need BP control: Aspirin is anti platelet agent. It helps prevent heart attack and strokes and should help in patients with high BP , but in your case it's more important to see a doctor and get your BP under control. Dr jan.