药品指一切用作诊断、治疗、预防疾病或减轻痛楚的药物或化学物质。可能是单一的活性成份，或是由多种活性成份组合而成。

药物治疗可以依多种方法分类，其中最常见的是以化学性质、功效、受影响身体部位或者是治疗效果分类。世界卫生组织（WHO）在1976年推出的解剖学治疗学及化学分类系统（ATC）受广泛应用，同时该组织还发布了一份基本药物列表。

以下列举一些药物分类的例子：

Pharmacotherapy is therapy using pharmaceutical drugs, as distinguished from therapy using surgery (surgical therapy), radiation (radiation therapy), movement (physical therapy), or other modes. Among physicians, sometimes the term medical therapy refers specifically to pharmacotherapy as opposed to surgical or other therapy; for example, in oncology, medical oncology is thus distinguished from surgical oncology.