While the pharmacy has arguably violated your privacy by accidentally disclosing some of your medical data, it is unlikely that you could recover anything for this--generally, to recover in a lawsuit or legal action, you must have suffered some damage or injury for which you can be compensated, and it's not at all clear that your mother knowing a medicine you are one actually injures in any significant way.Also, the law does not compensate for "might have beens" or "near misses." IF your father actually took the wrong medicine and was injured, then there very likely would be a cause of action. But the mere fact that he *could* have been injured does not provide any basis for  compensation if he was fortunate enough to not have taken the medicine, or to have taken it and not suffered ill effects.