The subquest to find food in the Super Duper Mart from the three part quest Wasteland Survival Guide given by Moira in Megaton requires you to optionally find medicine inside the Super Duper Mart. Unfortunately, in the same area where the fridge is looted to find the food, a "pharmacy key" is to be found, which is nothing but a red herring for this quest.
In fact, the meds can be found inside a barely visible first aid kit mounted on the all next to the terminal that releases the Protectron.