Translation:The pain will have gone away after I take the medicine.
Sorry. I can't think of any situation when this construction would be used in English. It is extremely clumsy. And nearly meaningless. Maybe "The pain will go away after I take the medicine." Or, "The pain will have gone away by the time I take the medicine." Or even, "The pain will pass because I take (or took) the medicine" But the way Duo wrote it, I can't see it. I'm open to suggestions, though. I love nothing more than to be proven wrong.