The Crown Prince That Sells Medicine is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

[By the Author that brought you !] I’m the crown prince? The frail and sickly crown prince in the novel? But I’m a traditional Korean medicine doctor. I guess it can’t be helped. Reforming internal constitution, recovering of energy, invigorating vital energy, and increasing vitality. I’ll take care of my body from now on.