Epinephrine (also known as adrenaline) is a hormone and a neurotransmitter. Epinephrine has many functions in the body, regulating heart rate, blood vessel and air passage diameters, and metabolic shifts; epinephrine release is a crucial component of the fight-or-flight response of the sympathetic nervous system. In chemical terms, epinephrine is one of a group of monoamines called the catecholamines. It is produced in some neurons of the central nervous system, and in the chromaffin cells of the adrenal medulla from the amino acids phenylalanine and tyrosine.

This chemical is widely referred to as "adrenaline" outside the United States; however, its United States Adopted Name and International Nonproprietary Name is epinephrine. Epinephrine was chosen as the generic name in the United States because John Abel, who prepared extracts from the adrenal glands in 1897, used that name for his extracts. In 1901, Jokichi Takamine patented a purified adrenal extract, and called it "adrenalin", which was trademarked by Parke, Davis & Co in the US. In the belief that Abel's extract was the same as Takamine's, a belief since disputed, epinepherine became the generic name in the US. The British Approved Name and European Pharmacopoeia term for this chemical is adrenaline and is indeed now one of the few differences between the INN and BAN systems of names.