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Endorphins (contracted from "endogenous morphine"[1][2]) are endogenous opioid neuropeptides and peptide hormones in humans and other animals. They are produced and stored in the pituitary gland. The classification of molecules as endorphins is based on their pharmacological activity, as opposed to a specific chemical formulation.

The endorphin class consists of α-endorphin, β-endorphin, and γ-endorphin. All three preferentially bind to μ-opioid receptors.[3] The principal function of endorphins is to inhibit the communication of pain signals. Endorphins may also produce a feeling of euphoria very similar to that produced by other opioids.[4]


Opioid peptides in the brain were first discovered in 1974 by two independent groups of investigators:

Studies have subsequently distinguished between enkephalins, endorphins, and endogenously produced morphine,[9][10] which is not a peptide.


The word endorphin is derived from ἔνδον / Greek: éndon meaning "within" (endogenous, ἐνδογενής / Greek: endogenes, "proceeding from within"), and morphine, from Morpheus (Ancient Greek: Μορφεύς, romanizedMorpheús), the god of dreams in the Greek mythology. Thus, endorphin is a contraction of 'endo(genous) (mo)rphin' (morphin being the old spelling of morphine).


The class of endorphins consists of three endogenous opioid peptides: α-endorphin, β-endorphin, and γ-endorphin.[3] α-endorphin is the smallest, and β-endorphin is the largest.

Name Sequence Reference
α-endorphin Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-OH [11]
β-endorphin Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-Phe-Lys-Asn-Ala-Ile-Ile-Lys-Asn-Ala-Tyr-Lys-Lys-Gly-Glu [12][13]
γ-endorphin Tyr-Gly-Gly-Phe-Met-Thr-Ser-Glu-Lys-Ser-Gln-Thr-Pro-Leu-Val-Thr-Leu-OH [11]


Endorphins are produced in the pituitary gland. All three types of endorphins are fragments of the precursor protein proopiomelanocortin (POMC). POMC is fragmented into many different smaller proteins, including beta-lipotropin (β-LPH). β-LPH, a pituitary hormone with little opiate activity, is then continually fragmented into different peptides, including α-endorphin, β-endorphin, and γ-endorphin.[13][14][15]

Mechanism of action[edit]

Endorphins are released from the pituitary gland in response to pain and can act in both the central nervous system (CNS) and the peripheral nervous system (PNS). In the PNS, β-endorphin is the primary endorphin released from the pituitary gland. Endorphin binding at μ-receptors inhibits pain signals in peripheral nerves by blocking the neurotransmitter substance P. The mechanism in the CNS is similar but works by blocking a different neurotransmitter: gamma-aminobutyric acid (GABA). In turn, inhibition of GABA increases the production and release of dopamine, the neurotransmitter associated with pleasure.[12][16]


Endorphins play a major role in the body's inhibitory response to pain. For example, endorphin release is responsible for producing the euphoric state in cases such as runner's high, sex, orgasm, listening to music, and eating appetizing food such as chocolate.[12][17] Research has demonstrated that meditation by trained individuals can be used to trigger endorphin release.[17] Laughter may also stimulate endorphin production and elevate one's pain threshold.[18]

Endorphin production can also be triggered by vigorous aerobic exercise. β-endorphin release contributes to a phenomenon known as a "runner's high."[19][20] Endorphins may contribute to the positive effect of exercise on anxiety and depression.[21] The same phenomenon may also play a role in exercise addiction. Regular intense exercise may cause the brain to downregulate the production of endorphins in periods of rest to maintain homeostasis, causing a person to exercise more intensely in order to receive the same feeling.[22]


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  14. ^ Crine P, Gianoulakis C, Seidah NG, Gossard F, Pezalla PD, Lis M, Chrétien M (October 1978). "Biosynthesis of beta-endorphin from beta-lipotropin and a larger molecular weight precursor in rat pars intermedia". Proceedings of the National Academy of Sciences of the United States of America. 75 (10): 4719–23. doi:10.1073/pnas.75.10.4719. PMC 336191. PMID 216997.
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