Medicine, huh, what kind of medicine keeps working when you stop taking it, breasts that big don't grow before you realize it, so the only thing I can say is that the MC kept taking them after the changes started, so he's an idiot for not realizing they were the cause.
The only way to escape it is through surgery now, so it's his own fault for letting it get that far, who even takes medicine that they don't know what they do, "I meant to take some cold medicine, but I didn't read what it was, so now I have tits" the MC is lucky to even be alive, he could have taken poison thinking it was medicine with his stupidity.