The phrase "to be someone's medicine" means to have a positive impact on that person, to help them heal or grow in some way. It is often used metaphorically and can refer to anything from a kind word or action, to a personal experience or relationship, to something as simple as a cup of tea. The idea behind the phrase is that each individual has their own unique medicine - something that brings them comfort, peace, or growth - and it's important for us to recognize what those things are and incorporate them into our lives when we need healing or support.