CID 5816

C₉H₁₃NO₃

Epinephrine

C 9
H 13
N 1
O 3

Ball-and-stick Stick Space-filling

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26 atoms, 26 bonds.

IUPAC name: 4-[(1R)-1-hydroxy-2-(methylamino)ethyl]benzene-1,2-diol
Molar mass: 183.207(25) g/mol
Atoms: 26
SMILES: CNCC(C1=CC(=C(C=C1)O)O)O
InChIKey: UCTWMZQNUQWSLP-VIFPVBQESA-N
PubChem CID: 5816

Made of

C H N O

Structural formula of epinephrine. Each unlabelled corner is a carbon atom, and the six hydrogens on carbon are not drawn. Wedges come toward you, hashes go back. It shows which atoms are joined to which, not the shape. The model above shows the shape.

Adrenaline and epinephrine are two names for one compound. The US Food and Drug Administration (FDA) describes it as both a hormone and a neurotransmitter, a term the serotonin page explains. Its release is a central part of the fight-or-flight response run by the sympathetic nervous system. The hypothalamus, in the brain, sets the adrenaline flowing during an exam or a job interview.

Nine carbon atoms, thirteen hydrogen, one nitrogen and three oxygen make up C₉H₁₃NO₃, 183.2 g/mol. The pure compound is an odourless white or nearly white powder of very fine crystals, as CAMEO Chemicals, a US hazards database, describes it. Water dissolves only 180 mg per litre at 20 °C, a figure from the Hazardous Substances Data Bank (HSDB), and CAMEO calls such solutions slightly alkaline. Mineral acids and sodium or potassium hydroxide solutions dissolve it readily. HSDB lists its pK_a, a measure of acid strength, as 8.28.

Structure and bonding

Epinephrine’s 26 atoms fall into three parts. A six-carbon ring carries O–H groups on two neighbouring carbons. The side chain, two carbons long, starts at a carbon holding a third O–H, the molecule’s one stereocentre. A nitrogen ends the chain, holding one hydrogen and a methyl group, CH₃. The model shows the stereocentre’s (R) form; the lactic acid page explains such mirror-image forms.

Labels marks a single N between the chain and the methyl carbon. Viewed along the ring’s edge in Stick, the ring, its two O–H groups and the chain’s first carbon share one plane. The chain’s oxygen and its CH₂ carbon sit 1.21 Å to either side of that plane. Space-filling shows the flat ring trailing a kinked tail. That twist is one computed conformer; single bonds are free to rotate.

In Ball-and-stick the ring’s bonds alternate double and single, yet all six measure 1.395 Å in the model. The pattern is one way of drawing a benzene ring, whose six bonds are alike. The uncharged molecule in the model can take up a proton to become a 1+ ion, which ChEBI (Chemical Entities of Biological Interest) names (R)-adrenaline(1+). Medicines hold it as a hydrochloride or bitartrate salt.

Where it turns up

In the body it comes from the adrenal medulla, the inner part of each adrenal gland, a gland the cortisol page describes. The medulla is mostly chromaffin cells, which produce and store it together with norepinephrine, according to Medical Subject Headings (MeSH). The last step in making it turns norepinephrine into epinephrine by adding the methyl group seen on the model’s nitrogen; the dopamine page sets out the earlier ones. Certain neurons in the central nervous system make it as well.

As a medicine it has been extracted from sheep and cattle adrenal glands or synthesised from pyrocatechol, according to HSDB. The synthetic route’s mirror-image forms are separated using d-tartaric acid. A chlorofluorocarbon-propelled epinephrine inhaler was approved in the United States in 1967 for sale without prescription against asthma symptoms. It left the market in 2011, when such propellants were phased out under the Montreal Protocol, an agreement described under dichlorodifluoromethane.

Why it matters

Epinephrine stimulates two sets of receptors, alpha and beta. Acting on alpha receptors, it narrows blood vessels, which raises blood pressure, according to the US National Cancer Institute’s NCI Thesaurus. Through beta receptors it makes the heart beat harder and faster and relaxes the smooth muscle of the airways, widening them.

HSDB calls it the first-choice drug when a severe allergic reaction needs emergency treatment, as in anaphylaxis, the life-threatening reaction described under histamine. Its other uses include asthma, cardiac arrest, glaucoma and stopping bleeding on a surface. Added to some local anaesthetics, it slows their absorption into the blood, which keeps the numbing local and makes it last longer.

Beta-blockers, as the National Cancer Institute defines them, stop substances such as adrenaline from acting on nerve cells, lowering blood pressure and heart rate. A phaeochromocytoma, a tumour in the middle of an adrenal gland, makes the gland produce too much adrenaline. Epinephrine carried in the blood crosses the placenta, HSDB reports, but not the blood–brain barrier described under dopamine.

Properties

Properties of epinephrine Molar mass summed from IUPAC/CIAAW 2024 standard atomic weights; formula, atom and bond counts and PubChem's molecular weight from PubChem CID 5816.
Property	Value	Unit	Source
Molecular formula (Hill order)	C₉H₁₃NO₃
Molar mass	183.207(25) g/mol	g/mol	IUPAC/CIAAW 2024
Carbon atoms	9
Hydrogen atoms	13
Nitrogen atoms	1
Oxygen atoms	3
Bonds	26
Single bonds	23
Double bonds	3
PubChem molecular weight	183.2 g/mol	g/mol	PubChem

Safety

Pure epinephrine is classed as fatal in contact with skin, and as toxic if swallowed or inhaled, under the signal word Danger. Those are the Globally Harmonized System (GHS) classifications that companies have notified to the European Chemicals Agency. They are classifications of the pure chemical. The full list is in the PubChem Laboratory Chemical Safety Summary for epinephrine.

Questions

Is epinephrine the same as adrenaline?

Yes. Epinephrine is also known as adrenaline, in the words of the US Food and Drug Administration (FDA): one hormone, C₉H₁₃NO₃, under two names. It first came from adrenal gland extracts, which Jokichi Takamine purified in 1901 and called adrenalin. The firm that sold the product from that year trademarked the name Adrenalin. It has been on sale in the United States in one formulation or another ever since.

Why is epinephrine used for anaphylaxis?

Anaphylaxis is a life-threatening allergic reaction that usually affects several parts of the body. Epinephrine opens the airways and raises blood pressure, as MedlinePlus explains, and the US Food and Drug Administration (FDA) calls it the only life-saving treatment for the condition. In August 2024 the FDA approved a nasal spray, the first epinephrine product for anaphylaxis that is not injected. The agency noted that fear of injections may lead some people, children especially, to delay or avoid treatment.

Why is epinephrine injected instead of swallowed?

Swallowed epinephrine is not effective, because the lining of the gut and the liver rapidly alter it by conjugation and oxidation, the Hazardous Substances Data Bank (HSDB) reports. Its action in the body is brief as well, ended mainly by uptake and breakdown in sympathetic nerve endings. The enzymes catechol-O-methyltransferase and monoamine oxidase take part, and the main products, metanephrine and vanillylmandelic acid, are both inactive. Injection was the first route in wide use; inhalation came later.

How is epinephrine made from norepinephrine?

By adding a methyl group. An enzyme, phenylethanolamine N-methyltransferase, converts norepinephrine into epinephrine, according to Medical Subject Headings (MeSH), and takes the methyl from a donor molecule, S-adenosyl-L-methionine. In the 3D model that methyl is the CH₃ on the nitrogen, the methylamino group of the systematic name. Besides that methylamino group, the model's 26 atoms form a six-carbon ring with two O–H groups and a two-carbon chain carrying a third.

Why does epinephrine solution turn pink?

Oxidation is the cause. The Hazardous Substances Data Bank (HSDB) reports that oxidising the drug gives first a pink colour and then a brown one. The red that develops when neutral or alkaline solutions stand in air comes from a product named adrenochrome. Some commercial injections are therefore packed under nitrogen in place of air, which keeps the oxidation from starting.

Made of the same elements

C₉H₁₁NO₃ Tyrosine 24 atoms, 24 bonds.
C₉H₁₁NO₂ Phenylalanine 23 atoms, 23 bonds.
C₈H₁₁NO₂ Dopamine 22 atoms, 22 bonds.
C₆H₁₃NO₂ Isoleucine 22 atoms, 21 bonds.
C₆H₁₃NO₂ Leucine 22 atoms, 21 bonds.
C₁₀H₁₂N₂O Serotonin 25 atoms, 26 bonds.
C₁₁H₁₂N₂O₂ Tryptophan 27 atoms, 28 bonds.
C₈H₉NO₂ Acetaminophen 20 atoms, 20 bonds.

All 25 compounds made of carbon, hydrogen, nitrogen and oxygen

C₈H₁₀N₄O₂ Caffeine 24 atoms, 25 bonds.
C₁₂H₁₇NO DEET 31 atoms, 31 bonds.
C₅H₉NO₄ Glutamic acid 19 atoms, 18 bonds.
C₁₃H₁₆N₂O₂ Melatonin 33 atoms, 34 bonds.
C₁₃H₂₁NO₃ Albuterol 38 atoms, 38 bonds.
C₃H₇NO₂ Alanine 13 atoms, 12 bonds.
C₁₄H₁₈N₂O₅ Aspartame 39 atoms, 39 bonds.
C₅H₆N₂O₂ Thymine 15 atoms, 15 bonds.
C₂H₅NO₂ Glycine 10 atoms, 9 bonds.
C₄H₄N₂O₂ Uracil 12 atoms, 12 bonds.
C₅H₄N₄O₃ Uric acid 16 atoms, 17 bonds.
C₄H₅N₃O Cytosine 13 atoms, 13 bonds.
C₁₄H₂₂N₂O Lidocaine 39 atoms, 39 bonds.
C₁₇H₂₁NO Diphenhydramine 40 atoms, 41 bonds.
C₅H₅N₅O Guanine 16 atoms, 17 bonds.
CO(NH₂)₂ Urea 8 atoms, 7 bonds.
C₂₀H₂₄N₂O₂ Quinine 48 atoms, 51 bonds.