The Spanish word "medicinas," the plural form of "medicina," simply refers to medicine used for the treatment and prevention of diseases and illnesses. In English, medicine is used both as a singular and plural noun.
Medicine (medicina) has two meanings in both English and Spanish. First, it can be used as a noun (always singular) that refers to medical science. For example, the English term "alternative medicine" translates to "medicina alternativa" in Spanish.
The second meaning of medicine pertains to a compound used to treat or prevent diseases and illnesses. This usage can be either singular or plural, which is why "medicinas" must fall into this second meaning and is a synonym of "medicamentos." The noun "medicamento" is only used with this meaning and is more common than the form "medicinas."