Potions can be purchased at an Apothecary while in Street View or at the Store in Map View.
Health Potions Edit
Health potions come in handy when you want to fight at a higher level to get more XP. Health potions are subject to the influence discount; therefore they are cheaper if you buy them in Street View by visiting an Apothecary where you have the most Influence. Potions can also be bought and used in dungeons. You can heal up between floors by clicking the Plus icon on the injured character's profile. This gives you the option to use potions you have in your inventory as well as purchase more potions. During battle, you can use potions by clicking on the Inventory option and selecting the character to use the potion on.
Energy Potion Edit
Energy potions restore all of your MP, allowing you to continue further in dungeons without having to wait for your MP bar to increase, or to spend more energy to boost your influence.