Kusuri no Majoramu

The Mahou sisters, Ram and Yuki, run a pharmacy. Yuki looks like a normal adult, but Ramu looks like a child, despite being in her twenties. It has been a joke in the past that the Mahou Pharmacy dispenses magic medicine (Mahou is the word for magic, as well as their last name), but now the joke is actually true! Ram started studying magic, donned a witch's hat, and now provides magical treatments for their customers. This 4-koma follows their life, dispensing both medicine and magic to customers with various ailments.

(Source: MangaHelpers)