麻黄碱，又称麻黄素（ephedrine，缩写：EPH）是一种拟交感神经胺，可用来预防腰椎麻醉时可能引发的低血压症状，也会在治疗气喘、猝睡症以及肥胖症中使用，但效果有限，且副作用太大，现已改用其他替代品。使用方法包括口服或借由肌肉或静脉注射，也可透过皮下注射。静脉注射的麻醉效果最快显现，其次是肌肉注射，大约需要20分钟的作用时间，而经由口服大约需一小时。当使用注射方式给予麻黄素时，麻醉时效可持续约一小时，口服方式则可维持达四小时之久。麻黄碱也用作兴奋剂，食欲抑制剂，集中精力及解除鼻塞等。麻黄素与其人工合成的衍生物安非他命、甲基安非他命的结构类似。化学上属于一种生物碱，源于麻黄属植物。常以盐酸盐或硫酸盐的形式出售。

Ephedrine is a medication used to prevent low blood pressure during spinal anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It can be taken by mouth or by injection into a muscle, vein, or just under the skin. Onset with intravenous use is fast, while injection into a muscle can take 20 minutes, and by mouth can take an hour for effect. When given by injection it lasts about an hour and when taken by mouth it can last up to four hours.