How can taking coreg (carvedilol) 12.5mg 2 a day cause erectile dysfunction?

Maybe (not) . . .: Carvedilol (coreg) doesn't list erectile dysfunction as a side effect at https://online.Epocrates.Com/noframe/showpage.Do?Method=drugs&monographid=533 & http://www.Drugs.Com/carvedilol.Html. But many blood pressure medications, including beta blockers in general, are associated w/ed. Obesity, high cholesterol, high sugars, etc are also associated w/ed. These are commonly associated w/high bp.

Generally not: Usually not, but in a specific person it is impossible to say for certainty. Try going off the medication for a period of time (with your doctor's approval of course) and see if thing improve.