@FappityFappityFap Coca Cola was a "nerve tonic" I think. When first sold it was claimed it could cure morphine addiction, indigestion, nerve disorders, headaches, and impotence. It was marketed as a "temperance drink" i.e. alcohol free, which given it contained cocaine (up to 9mg per glass) until 1903 is a little ironic.
I'm not reading a manga about a drug kingpin peddling narcotics am I?
Its fun to see how many people in the comments have picked up on the origins of popular soft drinks. He just needs to go the route of CocaCola, Dr.Peper, etc.. and drop the dodgy "medicines" while keeping the taste.
So not only was she not actually sick, but he gives her five potions a day for free. He really doesn't need this word of mouth help, everyone in town pretty much trusts him already by now? Can't run a business by feeling sorry for customers with poor impulse control.