No, you couldn't use warehouse in this context. If it's a room where the pharmacy keeps their supplies, you could call it a store room or a stock room.
'House' means building, and a warehouse is a large, independent building. Products would typically be transported from the factory to a warehouse, where they'd be stored in large quantities before being shipped out to retailers or customers. A large retailer might have its own warehouse, but this would be a separate building from the retail premises.