药物（英语：Drug）广义上指可以对人或其他动物产生已知生物效应的物质。食物通常不适用于这个定义，尽管它们可以对生物物种产生生理效应。

药理学上，药物指用于预防、治疗、诊断疾病或增强体格或改善精神状态的化学物质。 药品可以短期使用或定期使用来治疗慢性疾病。

精神药物是可以影响神经系统功能，改变感觉、情绪、意识的化学物质。 酒精、尼古丁和咖啡是世界上使用最广泛的精神药物。

娱乐性药物是没有医疗用途，而是用来获得快感的药物。 常见的娱乐性药物包括酒精、尼古丁和咖啡因，也包括其他物质如鸦片类药物和安非他命。

A pharmacon or pharmakon (from Greek: (φάρμακον), adapted from pharmacos) is a biologically active substance. It is used more broadly than the term drug because it includes endogenous substances, and biologically active substances which are not used as drugs. Typically the word pharmacon includes, pharmacological agonists and antagonists, but also enzyme inhibitors (such as monoamine oxidase inhibitors) etc. Spelt with a "k", is acceptable in English, but more common in German. In most cases pharmacon is the equivalent to active ingredient.