Final answer:
The most dangerous side effect an athlete would likely experience from performance-enhancing drug use is high blood pressure.
Step-by-step explanation:
If an athlete participates in performance-enhancing drug use, a physician would MOST LIKELY expect the athlete to experience high blood pressure as a dangerous side effect. Performance-enhancing drugs, such as anabolic steroids, can increase the production of red blood cells and cause blood vessels to constrict, leading to elevated blood pressure levels. This can put strain on the heart and increase the risk of cardiovascular diseases.
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