Exercising while taking certain medications can be dangerous. For instance:
Aspirin can hide the pain that would normally tell you that it is time to stop.
Antihistamines make you drowsy and can put a strain on your muscles and heart.
Taking a decongestant raises your blood pressure which can lead to heart attacks and/or stroke.
Diuretics cause dehydration and cramping.
Tranquilizers hide pain and dull reflexes.
Make sure to check with your doctor before mixing medications and exercise. Also, see how your body reacts to your medication before exercising.