The term "necessary medicine" is a common expression that refers to any medication or treatment that is required for maintaining good health, managing an existing medical condition, or preventing the worsening of a disease. In other words, it's a type of prescription drug or over-the-counter remedy that is essential for promoting wellness and addressing specific health concerns. The phrase can also be used more broadly to refer to any intervention or action that is necessary for achieving a desired outcome, whether in the context of medicine, business, politics, or other areas of life.