Ephedrine is a central nervous system (CNS) stimulant that is often used to prevent low blood pressure during anesthesia. It has also been used for asthma, narcolepsy, and obesity but is not the preferred treatment. It is of unclear benefit in nasal congestion. 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.

Common side effects include trouble sleeping, anxiety, headache, hallucinations, high blood pressure, fast heart rate, loss of appetite, and inability to urinate. Serious side effects include stroke and heart attack. While likely safe in pregnancy, its use in this population is poorly studied. Use during breastfeeding is not recommended. Ephedrine works by increasing the activity of the α and β adrenergic receptors.

Ephedrine was first isolated in 1885 and came into commercial use in 1926. It is on the World Health Organization's List of Essential Medicines. It is available as a generic medication. It can normally be found in plants of the Ephedra genus. Dietary supplements containing ephedrine are illegal in the United States, with the exception of those used in traditional Chinese medicine, where its presence is noted by má huáng.