Epinephrine, also known as adrenaline, is a hormone and neurotransmitter secreted primarily by the adrenal glands . It plays a crucial role in the body's fight-or-flight response to stress, preparing the body for intense physical activity by increasing cardiac output and raising blood glucose levels. Epinephrine is a type of catecholamine , closely related to norepinephrine. It is synthesized from the amino acid tyrosine. Clinically, epinephrine is used to treat severe allergic reactions like anaphylaxis and is administered via devices like the epinephrine autoinjector . It acts on adrenergic receptors, influencing various bodily functions, including blood vessel constriction and dilation, heart rate, and the breakdown of glycogen into glucose.

Where is epinephrine produced in the body?

Epinephrine, also known as adrenaline, is primarily produced in the adrenal medulla , which is the inner part of the adrenal glands . These glands are located near the kidneys. Small amounts of epinephrine are also released from the ends of sympathetic nerves. The production process begins with the amino acid tyrosine, which is converted through a series of reactions into norepinephrine, and then methylated to form epinephrine. This hormone plays a crucial role in the body's "fight or flight" response to stress.

What is the main job of epinephrine in our body?

Epinephrine, also known as adrenaline, is a hormone and neurotransmitter that plays a crucial role in the body's fight-or-flight response to stress or danger. Its primary job is to prepare the body for intense physical activity. When epinephrine is released, it increases heart rate and blood pressure, diverts blood flow to muscles, and raises blood glucose levels by stimulating the breakdown of glycogen in the liver. These actions provide the body with the necessary energy and oxygen for immediate action, whether it's to confront a threat or escape from it. Epinephrine also causes the pupils to dilate, improving vision.

How does epinephrine help us in stressful situations?

Epinephrine, also known as adrenaline, is a hormone released by the adrenal glands during stressful situations, preparing the body for a "fight or flight" response. This response increases heart rate and blood pressure, dilates blood vessels to enhance blood flow to the brain and muscles, and raises blood glucose levels for immediate energy. These physiological changes help an individual react effectively to perceived threats. Epinephrine also dilates pupils for improved vision and relaxes airway muscles to facilitate breathing.

What changes happen in the body when epinephrine is released?

When epinephrine is released, it triggers the body's "fight-or-flight" response, preparing an individual for acute stress. This hormonal surge increases heart rate and cardiac output, leading to higher blood pressure. Epinephrine also causes blood vessels to constrict in many areas but dilate in skeletal muscles and the liver, redirecting blood flow. Furthermore, it stimulates the breakdown of glycogen in the liver into glucose, raising blood sugar levels to provide readily available energy. Additionally, epinephrine increases the level of circulating free fatty acids, another fuel source for the body during times of stress. These physiological changes enhance alertness and prepare the body for intense physical exertion.

How is epinephrine used in medicine, like for allergic reactions?

Epinephrine, also known as adrenaline, is a hormone crucial for treating severe allergic reactions like anaphylaxis. It is administered via an epinephrine autoinjector, a device designed for rapid self-injection, typically into the thigh. When anaphylaxis occurs, the immune system overreacts to an allergen, leading to symptoms such as throat tightness, breathing difficulties, and low blood pressure. Epinephrine counteracts these effects by constricting blood vessels to raise blood pressure, relaxing lung muscles to improve breathing, and stimulating the heart. While other medications can manage some allergy symptoms, only epinephrine can rapidly reverse anaphylactic reactions, potentially preventing hospitalization and fatality. Epinephrine autoinjectors are prescribed to individuals at high risk of severe allergic reactions, including those with food allergies or severe reactions to insect stings.

Epinephrine

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Images

Diagram showing how epinephrine binding to a beta-adrenergic receptor on a cell membrane activates a G-protein, which then stimulates adenylyl cyclase to convert ATP into cyclic AMP (cAMP), leading to physiological effects such as increased heart rate, blood vessel dilation, and glycogen breakdown.

Two EpiPen auto-injectors with yellow labels and blue caps are shown in front of a yellow EpiPen 2-Pak box, used for emergency allergic reaction treatment.

Diagram showing the organization of the autonomic nervous system, with labeled pathways for parasympathetic and sympathetic nerves, highlighting synapses, neurotransmitters like acetylcholine and norepinephrine, and their receptor types.

At a Glance

epinephrine summary

Quick Facts

Also called:: adrenaline

Key People:: Jokichi Takamine; Sir Edward Albert Sharpey-Schafer; John Jacob Abel

Related Topics:: adrenal gland; adrenochrome; epinephrine autoinjector; Glycogenolysis; adrenal medulla

On the Web:: National Center for Biotechnology Information - Epinephrine (Nov. 07, 2026)

See all related content

Epinephrine

hormone

Also known as: adrenaline

Written by

Kara Rogers

Fact-checked by

Britannica Editors

Last updated

Nov. 11, 2026 •History

Top Questions

What is epinephrine?
Epinephrine, also known as adrenaline, is a hormone and neurotransmitter secreted primarily by the adrenal glands. It plays a crucial role in the body's fight-or-flight response to stress, preparing the body for intense physical activity by increasing cardiac output and raising blood glucose levels.

Epinephrine is a type of catecholamine, closely related to norepinephrine. It is synthesized from the amino acid tyrosine. Clinically, epinephrine is used to treat severe allergic reactions like anaphylaxis and is administered via devices like the epinephrine autoinjector. It acts on adrenergic receptors, influencing various bodily functions, including blood vessel constriction and dilation, heart rate, and the breakdown of glycogen into glucose.
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Where is epinephrine produced in the body?
Epinephrine, also known as adrenaline, is primarily produced in the adrenal medulla, which is the inner part of the adrenal glands. These glands are located near the kidneys. Small amounts of epinephrine are also released from the ends of sympathetic nerves. The production process begins with the amino acid tyrosine, which is converted through a series of reactions into norepinephrine, and then methylated to form epinephrine. This hormone plays a crucial role in the body's "fight or flight" response to stress.
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Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What is the main job of epinephrine in our body?
Epinephrine, also known as adrenaline, is a hormone and neurotransmitter that plays a crucial role in the body's fight-or-flight response to stress or danger. Its primary job is to prepare the body for intense physical activity.

When epinephrine is released, it increases heart rate and blood pressure, diverts blood flow to muscles, and raises blood glucose levels by stimulating the breakdown of glycogen in the liver. These actions provide the body with the necessary energy and oxygen for immediate action, whether it's to confront a threat or escape from it. Epinephrine also causes the pupils to dilate, improving vision.
7 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How does epinephrine help us in stressful situations?
Epinephrine, also known as adrenaline, is a hormone released by the adrenal glands during stressful situations, preparing the body for a "fight or flight" response. This response increases heart rate and blood pressure, dilates blood vessels to enhance blood flow to the brain and muscles, and raises blood glucose levels for immediate energy. These physiological changes help an individual react effectively to perceived threats. Epinephrine also dilates pupils for improved vision and relaxes airway muscles to facilitate breathing.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
What changes happen in the body when epinephrine is released?
When epinephrine is released, it triggers the body's "fight-or-flight" response, preparing an individual for acute stress. This hormonal surge increases heart rate and cardiac output, leading to higher blood pressure. Epinephrine also causes blood vessels to constrict in many areas but dilate in skeletal muscles and the liver, redirecting blood flow.

Furthermore, it stimulates the breakdown of glycogen in the liver into glucose, raising blood sugar levels to provide readily available energy. Additionally, epinephrine increases the level of circulating free fatty acids, another fuel source for the body during times of stress. These physiological changes enhance alertness and prepare the body for intense physical exertion.
6 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.
How is epinephrine used in medicine, like for allergic reactions?
Epinephrine, also known as adrenaline, is a hormone crucial for treating severe allergic reactions like anaphylaxis. It is administered via an epinephrine autoinjector, a device designed for rapid self-injection, typically into the thigh.

When anaphylaxis occurs, the immune system overreacts to an allergen, leading to symptoms such as throat tightness, breathing difficulties, and low blood pressure. Epinephrine counteracts these effects by constricting blood vessels to raise blood pressure, relaxing lung muscles to improve breathing, and stimulating the heart. While other medications can manage some allergy symptoms, only epinephrine can rapidly reverse anaphylactic reactions, potentially preventing hospitalization and fatality. Epinephrine autoinjectors are prescribed to individuals at high risk of severe allergic reactions, including those with food allergies or severe reactions to insect stings.
5 Britannica Sources
Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

Epinephrine, hormone that is secreted mainly by the medulla of the adrenal glands and that functions primarily to increase cardiac output and to raise glucose levels in the blood. Epinephrine typically is released during acute stress, and its stimulatory effects fortify and prepare an individual for either “fight or flight” (see fight-or-flight response).

Epinephrine is closely related in structure to norepinephrine, differing only in the presence of a methyl group on the nitrogen side chain. In both substances, the amine (nitrogen-containing) group is attached to a catechol group (a benzene ring with two hydroxyl groups)—a structure unique to the catecholamines. Both substances are key stimulatory components of the sympathetic nervous system (part of the autonomic nervous system), hence their pharmacological classification as sympathomimetic agents.

Production of epinephrine

Epinephrine is produced specifically in the adrenal medulla, where the amino acid tyrosine is transformed through a series of reactions to norepinephrine. An enzyme known as phenylethanolamine N-methyltransferase, which is found in the chromaffin cells of the adrenal medulla, catalyzes the methylation of norepinephrine to epinephrine. In addition to the release of epinephrine from the adrenal glands, small amounts of the hormone are also released from the ends of sympathetic nerves.

Diagram comparing action potential conduction in myelinated and unmyelinated axons, showing a neuron with labeled cell body, myelin sheath, nodes of Ranvier, and the flow of electrical signals along each type of axon.

Physiological actions

The actions of epinephrine are complex, owing to its stimulatory effects on α- and β-adrenergic receptors (or adrenoceptors, so named for their reaction to the adrenal hormones), which produce various responses, depending on the specific receptor and the tissue in which it occurs. Hence, epinephrine causes constriction in many networks of minute blood vessels but dilates the blood vessels in the skeletal muscles and the liver. In the heart, it increases the rate and force of contraction, thus increasing the output of blood and raising blood pressure.

In the liver, epinephrine stimulates the breakdown of glycogen to glucose, resulting in an increase in glucose levels in the blood. It also acts to increase the level of circulating free fatty acids. The extra amounts of glucose and fatty acids can be used by the body as fuel in times of stress or danger, when increased alertness and exertion are required. Epinephrine also causes contraction of the dilator muscles of the iris in the eye, resulting in mydriasis (dilation of the pupil) and improved visual acuity. The physiological actions of epinephrine are terminated by metabolic breakdown with catechol-O-methyltransferase (COMT) or monoamine oxidase (MAO), by reuptake into nerve endings, and by diffusion from active sites.

Clinical significance

Purified active epinephrine is obtained from the adrenal glands of domesticated animals or prepared synthetically for clinical use. Epinephrine may be injected into the heart during cardiac arrest to stimulate heart activity. Epinephrine is also used to treat anaphylaxis (acute systemic allergic reaction), which can occur in response to exposure to certain drugs, insect venoms, and foods (e.g., nuts and shellfish). It is also occasionally used in the emergency treatment of asthma, where its relaxation of smooth muscle helps to open the airways in the lungs, and in the treatment of glaucoma, where it appears to both decrease the production of aqueous humor and increase its outflow from the eye, thereby lowering intraocular pressure. In turn, certain disease states are associated with abnormalities in epinephrine production and secretion. For example, epinephrine and other catecholamines are secreted in excessive amounts by pheochromocytomas (tumors of the adrenal glands).

Discovery of epinephrine

Epinephrine was discovered in the late 1800s. English physiologists George Oliver and Sir Edward Albert Sharpey-Schafer were among the first to describe the blood-pressure-raising effect of a substance from the adrenal medulla. By 1900 epinephrine had been isolated and identified by American physiological chemist John Jacob Abel and, independently, by Japanese American biochemist Jokichi Takamine. In 1904 German chemist Friedrich Stolz became the first to synthesize the hormone.

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