It happened at 12:30 p.m. Wednesday at the North Philly Pharmacy in the 2100 block of North 6th Street.
Police say three men wearing masks, two of them brandishing handguns, walked into the business and ordered everyone to the floor.
They forced the owner into a back room and stole 25 bottles of the painkiller Percoset, $50 cash and a customer's cell phone.
They were last seen running south on 6th Street.
Anyone with information about this crime or these suspects is asked to contact Philadelphia Police.