In some parts of the world, the terms epinephrine and adrenaline can be used interchangeably. The first name for this hormone was adrenaline, though epinephrine is now preferred throughout much of the world. In the United Kingdom and a few other countries, the official name for this hormone is still adrenaline. Though there is no difference between epinephrine and adrenaline, either in chemical composition or effect on the body, in some places, only one term or the other will be understood.

When it was first discovered in the end of the 19th century, the hormone that is now called both epinephrine and adrenaline was referred to only as adrenaline. This name is derived from the location of the adrenal glands which secrete the hormone and are found on top of the kidneys. "Adrenal" is made up of two Latin words that mean "on the kidneys." Though the hormone secreted by these glands can be called both epinephrine and adrenaline, the name for the glands themselves is always the same.

After the discovery of epinephrine and adrenaline, it was quickly adopted as a medical treatment. The hormone can be synthesized in a laboratory or extracted from animals, usually cows or sheep, and given to humans as an injection. This treatment is effective against cardiac arrest, shock, and anaphylaxis and has been used in emergency medicine since the beginning of the 20th century.

Once the drug became widely available, a number of pharmaceutical companies began to manufacture it. One of these companies took the name Adrenalin, causing some confusion as to whether the term referred to the name of the hormone or the brand name of the manufacturer. As a result, many nations adopted the term epinephrine to refer to the hormone instead of adrenaline. Epinephrine is a word made from a number of Greek roots, and like the word adrenaline, means "on top of the kidneys."

Though epinephrine and adrenaline are interchangeable terms in a number of countries, the preferred name for the hormone changes from nation to nation. In the United States, for example, epinephrine is the preferred term, though adrenaline is often used when discussing the hormone outside of the medical profession. An adrenaline junkie, for example, is a person who seeks thrills for the enjoyment of the feeling of fight or flight reaction created by the natural release of epinephrine. In the United Kingdom, on the other hand, the standard term is still adrenaline, and epinephrine is not officially recognized.