A 9 amino acid peptide hormone synthesized in the hypothalamus and released by the posterior lobe of the pituitary gland.

Functions of oxytocin:

milk letdown -- in lactating mothers, oxytocin stimulates myoepithelial cells, causing milk to be ejected into the ducts of the mammary glands. Sucking by the infant at the nipple stimulates oxytocin release.

uterine contraction -- necessary for cervical dilatation prior to birth and causes the contractions all mothers are familiar with. Obstetricians often inject some synthetic oxytocin after the baby is born to speed the delivery of the placenta.

inducing maternal behaviour -- this effect is a little more iffy and there is less evidence for it

plays some role in orgasms -- for both males and females. In males, oxytocin is said to facilitate sperm transport in ejaculation.

"What really gets me," my friend Holly says, "is the way I begin to spontaneously lactate whenever I hear a baby cry." She fiddles with her nursing bra, grins, and hitches baby Jason (fondly known as "Ace") up a bit higher on her lap. "In the weeks since my son was born, simply hearing a whimper in the supermarket from some random baby makes my milk come down immediately. It's just one more reminder that my body's not my own for a while. Not a bad thing, just...weird, you know?"

Oxytocin is responsible not only for Holly's lactation but for the feelings she has toward Jason. "Oh. My. God," Holly effuses when I ask her how she feels about her new son. "The way I feel about Ace? It's impossible to describe, but I'll try." She pauses to gaze adoringly into Jason's clear blue eyes. "Remember the butterflies you used to feel when you were first infatuated with your first boyfriend? It's like that, but it's wrapped up in deep, primal emotions that don't even have names. You could call it love, but that's such an inadequate little nothing of a word to describe how I feel about this child. It's like..." Holly casts about for the right word and looks up, intense. "It's like a romance, you know? I had an episiotomy, I haven't slept in weeks, I'm exhausted all the time, but it just doesn't matter. I feel as though I'm in this constant warm bath of emotions, like I'm floating in bliss. No matter how tired I am, I can't get enough of the way he looks when he sleeps. I watch him for hours. And the way he smells. The top of his head, you know? Milky-sweet, like fresh-baked bread with honey on top." Holly gets a dreamy, faraway look in her eyes as she inhales her son's scent. "I'd know his smell anywhere. Give me a hundred baby heads to sniff, and I'd know Ace's. This kid is the love of my life."

As I listen to Holly I smile. Can a simple chemical be responsible for such a tender torrent of emotions? Well, yes and no. Holly is obviously a well-adjusted woman who is blessed with a supportive, loving husband and a secure environment. She has no history of mental illness, and postpartum depression didn't trouble her mother or either of her sisters after they gave birth. It's reasonable to assume that Holly's living the gold standard of the "nurture" end of the "nature/nurture" dichotomy. But I'm intrigued by the "nature" angle, and oxytocin plays an enormous part in the love story between Holly and Jason. As I watch her cuddle and coo over her son, I realize I'm watching an ancient dance cleverly choreographed by evolution. Oxytocin is the music. It's the ecstatic hormonal soundtrack to every love story, maternal and otherwise, ever experienced.

In the last trimester of pregnancy, the human brain begins to secrete large amounts of oxytocin. Many women reminisce fondly about their final trimesters; despite memory lapses (also caused by oxytocin) and the inevitable weight gain, the increase of oxytocin creates a profound sense of well-being in most women during this part of pregnancy. Large numbers of oxytocin receptors are present in the uterus. The body begins labor by producing copious amounts of oxytocin, which signals the uterus to contract and expel the baby. After childbirth, oxytocin levels stay extremely high for several days, enabling the uterus to contract to nearly its pre-birth size and triggering lactation. Oxytocin has both mood-elevating and amnesiac qualities, which researchers believe combine to help women "forget" the pain of childbirth in order to attempt the ordeal all over again. Oxytocin bonds a mother to her child, and when levels are highest (during pregnancy and post-partum), the hormone elicits the single-minded devotion my friend Holly is currently feeling toward her son.

Oxytocin has been dubbed "the cuddle chemical" by zoologists who artificially raised the levels in goats and found that they exhibited the same behaviors as human mothers exhibit toward their newborn babies. Marijuana has been found to stimulate production of oxytocin, and some experts believe that smoking a little pot can be extremely beneficial to a flagging sex drive, particularly for women. Oxytocin is responsible for the uterine contractions that accompany menstruation and cause the expulsion of the uterine lining. As important as oxytocin is in the birth and menstrual process, its role in the non-procreative aspect of sex can't be overstated. Oxytocin is not simply released during orgasm, it seems to actually cause orgasm. At normal bodily levels, oxytocin encourages a mild underlying desire to kiss, nuzzle, and cuddle one's lover. Once the cuddling begins, oxytocin levels steadily rise, and the hormone stimulates the smooth muscles and sensitizes the nerves in erogenous zones such as the earlobes, the neck, and of course the genitals. As arousal builds and becomes more intense, production of oxytocin snowballs. Research suggests that oxytocin causes the nerves in the genitals to fire spontaneously, causing orgasm. Men's oxytocin levels have been found to quintuple during orgasm, but women's levels skyrocket. Women require more oxytocin to acheive orgasm, and the brain generously complies; because their brains are quite literally drenched in the chemical during peak sexual arousal, many women are able to achieve multiple and full body orgasms.

Oxytocin is unique among hormones in that its production can be triggered not only by physical but by emotional cues. The glance of a lover, the cry of a baby, or a certain gesture can all generate a flood of oxytocin. Butterflies in the tummy? Oxytocin. That warm, buttery feeling you get when you remember the fabulous sex you had on your honeymoon? Also oxytocin. Not surprisingly, it's responsible for a great deal of the bonding that goes on in a relationship. Because women produce such a massive overload of oxytocin during sex, it's thought to be the reason that women tend to bond more strongly and let go with greater difficulty once a relationship has progressed to a sexual dimension. That's not to say that men don't benefit from oxytocin; far from it. Though they don't rise to nearly the stratospheric heights as postpartum women enjoy, oxytocin levels in men do increase significantly when they hold and interact with their newborn children.

Oxytocin has other benefits as well. Healthy levels have been proven to reduce stress, regulate sleep patterns, and contribute to a general sense of well-being in both women and men. Stress has been proven to increase prolactin levels in women, a hormone that has been linked to breast cancer, brain tumors, and leukemia. Oxytocin regulates the body's production of prolactin, thereby decreasing one's risk of cancer. Interestingly, celibate women have a markedly higher risk of breast cancer than do women with active sex lives, even sexually active women who don't have early or multiple pregnancies (which have been proven to decrease breast cancer risk). Regular orgasms help to regulate oxytocin, as do intimate acts of cuddling and kissing. What a bonus. Good sex isn't just fun - it may actually help prevent cancer! It's also a natural anti-psychotic, and doctors have found that lithium actually regulates oxytocin production. Some forms of obsessive-compulsive disorder have been linked to oxytocin dysfunction.

Current research points to the benefits of oxytocin in the treatment of many kinds of addictions, particularly heroin and cocaine withdrawal. In rats, intravenous self-administration of both heroin and cocaine was significantly decreased when the rats were treated with oxytocin. Oxytocin also regulates appetite through receptors in the brain, inhibiting compulsive eating and preventing obesity. It's a natural antibiotic, and plays a role in fighting uterine infections. Finally, oxytocin's amnesiac qualities are essential in the necessary meltdown of old information in order to make room for new memory storage.

The human brain is a model of efficiency, and whenever possible it reuses convenient neural pathways. It makes perfect sense, therefore, that a woman would feel emotions akin to "romantic" toward her baby - the same neurological territory is utilized for bonding with a child and lovemaking alike. Breastfeeding causes oxytocin levels to rise so high that many women report experiencing orgasm-like sensations while nursing. It's all wrapped up in the same bundle of emotions and nerves and hormones. It's all part of the same messy, wonderful, oxytocin-fueled waltz.


Diane Ackerman. A Natural History of Love. New York: Random House, 1994.
"The Medical Need for Orgasms in Women". © Copyright 2001 - 2002 Artists Cooperative Groove Union U.A. Amsterdam, The Netherlands.
Susan E. Barker. 'The Cuddle Hormone’: Research links oxytocin and socio-sexual behaviors. http://www.oxytocin.org/cuddle-hormone/index.html
Linda Dopierala. Love, Neurochemistry, and Chocolate: A Word from Cupid, PH.D. CyberHealth #21, February, 1999. http://www.antiaging.com/cyberhealth/CyberHealth_21.html

Researching oxytocin takes you in one of two directions.

Explaining its chemistry is not something that can be done easily with plain language. Greek tells you that it means "quick birth." This tells you nothing.

Oxytocin is a nonapeptide. Peptides are combinations of amino acids. "nona" is nine — Oxytocin is a combination of nine amino acids. If you are a neurologist, you probably wrote down and memorized a mnemonic expressing the order of these acids to better reproduce them on an exam. You may have associated them with childbirth, with love, but having experienced neither the analogy became lifeless. When in love one has little time for mnemonics: oxytocin is bad for memory.

Oxytocin's chemical formula is C43H66N12O12S2. 1 You know that hydrogen combines with oxygen, producing water. You know that sulfur generates the stink in fertilizers. Diamonds and coal are made of carbon. Three-quarters of the air is nitrogen. You know that atoms quantify existence, but something is lost in the combination that produces oxytocin. The mathematics of chemistry express the universe in a self-referential language that works perfectly, and only, for those looking to understand the universe in terms of numbers.

The other direction in which one is taken while learning about oxytocin is more emotionally ambitious but equally dead. Oxytocin is the "cuddling chemical." Oxytocin makes you feel empathy. Sex and childbirth both involve lots of oxytocin. Cupid dips his arrows in oxytocin — how quaint. It is very easy to absorb information without learning.

I bought a few pounds of London broil today at the market for the first time in months. Oil prices are reflected in food: this cut, while large, was significantly more expensive than it would have been in January. Still cheap as meat goes.

Muscle tissue contains nerves. Oxytocin sometimes doubles as a neurotransmitter and occurs in mammals, like cattle. Cows lactate, their mammary glands emboldened by oxytocin. That their milk is everywhere numbs us to the meaning of this. "Lactate" is a term we save for mothers. Everyday, mothers pour their own milk into the sink.

I'll eat this steak tonight — rare. The proper term would probably be "blue." This will be an act of penance. The romantic in me likes to think that, having spared the interior much of the heat responsible for chemical breakdown, some molecules of the cuddling chemical will be absorbed into my own body. I know however that the resulting pangs of empathy will originate completely in my own nerves. This does not matter.


Social relations between humans critically depend on our affective experiences of others. Oxytocin enhances prosocial behavior, but its effect on humans' affective experience of others is not known. We tested whether oxytocin influences affective ratings, and underlying brain activity, of faces that have been aversively conditioned. Using a standard conditioning procedure, we induced differential negative affective ratings in faces exposed to an aversive conditioning compared with nonconditioning manipulation. This differential negative evaluative effect was abolished by treatment with oxytocin, an effect associated with an attenuation of activity in anterior medial temporal and anterior cingulate cortices.
Oxytocin Attenuates Affective Evaluations of Conditioned Faces and Amygdala Activity,2 from The Journal of Neuroscience.

More simply: oxytocin helps you recognize facial cues.

The amygdala is a funny thing. The term 'emotional memory' can be a difficult one to grasp.

Our grandmother spent a long time in Hospice seven years ago. After a bypass, and a stroke, and congestive heart failure, she deteriorated slowly enough so that each weekend was hypothesized to be her last. This happened several times. Doctors marveled at how long she survived. They were apologetic about it.

Not knowing what else to say, other family remarked that as a baby and an invalid one is more or less the same.

My sister gave birth to her first child, a daughter, at the end of May.

I drove to the desert and visited my niece the weekend after she was born. She had a concave mouth and a full head of black hair, even at six days old. She made faces, as babies will.

"She reminds me of Abuela," I said.

My sister, surprised, looked at her husband. "Didn't I say that? At the hospital?"

He nodded.

"It's really weird that you say that," she said. "They say that with reincarnation it's really rare for two lives to coincide one right after the other. I wonder if there's anything to that."

I said, "maybe," thinking about chemistry, and divinity.

Love is not an emotion.

Students who, by their own definition, were deeply in love were put into brain scanners at London's University College. Going on brain activity, their minds did not resemble those of emotional people (say, someone who's angry) — they looked like those of crack addicts.

Did I say love is not an emotion?

Wait until you wake up together for the first time. Wait until the shock of heat, greater than a body at rest can produce, at first touch. When it is so much you are aware of nothing, not even how desperately young people can feel certain things. Imagine that it's amino acids. Remember molecules from middle school. Something is missing.

Love is not an emotion.

An oft-cited example of oxytocin's role in commitment is in two species vole (of all animals) who share, naturally, 99% of their DNA. The short version: the species that produces it stays monogamous. Inject it into rats, animals which mate for the dopamine high, and find that they've adopted the sex habits of doves.

Did I say love is not an emotion?

Wait until she stops calling. I can still feel her before she comes home. A romantic might say that when the oxytocin wears off it's time to move on, but a scientist would remind you of crack addicts. I know her body produces the same warmth it did when I could not bring myself to notice whether the sun was shining. I know it's the same house we built together, the same air, the same California heat that mixed our sweat. The landscaping we coaxed out of irrigation and clay is dying. When she rests her head on my belly there is the same mitochondria, probably still oxytocin, but in her eyes something is missing.

Divinity, answers, are always in what is missing.

1 Wikipedia.
2 Authored by Predrag Petrovic, Raffael Kalisch, Tania Singer, and Raymond J. Dolan; available at http://www.jneurosci.org/cgi/content/abstract/28/26/6607.

Other sources:

University of California, San Francisco. "Hormone Involved in Reproduction May Have Role in the Maintenance of Relationships." http://www.oxytocin.org/oxytoc/.

doyle says re oxytocin: If you ever watch a woman in labor get an oxytocin drip (I think the trade name is Pitocin), watching the uterus just about rip itself apart, well, "quick birth" makes sense.

jessicaj says re oxytocin: I hesitate to contradict doyle but I was induced and it was anything but quick.


nb: originally from 2008

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