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Oxytocin acts as a 'love hormone'? Nah. The science reveals a much subtler effect on human behavior

The latest research calls into question oxytocin’s reputation as a direct promoter of trust or other virtuous social behaviors.

The neurotransmitter oxytocin has been given many nicknames, including the “love hormone,” the “hug hormone," the “cuddle chemical,” and even the “moral molecule.”

For decades, scientists have been demonstrating in various animals that oxytocin is involved in social interactions. It’s been shown to cause non-mated female rats to act maternally toward other rats’ young, for example, and to encourage prairie voles to form lifelong pairs. It can even make dogs gaze longer into their owners’ eyes.

But oxytocin’s fame as a social-enhancing hormone in humans stems from a 2005 study in Nature, which reported that people who inhaled a spray of oxytocin became more trusting of each other.

Not surprisingly, the supplement industry has taken advantage of the media headlines emanating from these research findings. You can now purchase oxytocin pills, drops and sprays “for relationships, connecting, stress, depression, and anxiety.”

Of course, there’s no evidence that oxytocin supplements help with any of those things. In fact, as science writer Ed Yong points out in a recent article for The Atlantic, the latest research calls into question oxytocin’s reputation as a direct promoter of trust or other virtuous social behaviors.

“Several scientists have shown that this tower of evidence for oxytocin’s positive influence is built on weak foundations,” he writes. “Gideon Nave at the California Institute of Technology found five other papers where researchers had used similar trust games to those in the original Nature experiment. None of these found that a sniff of oxytocin could significantly boost trust. And when the team combined the results of all six studies, they couldn’t find an effect either.”

“These criticisms don’t just apply to studies on trust,” Yong adds, “but to those on altruism, cooperation, and other behaviors that oxytocin supposedly boosts. When Larry Young from Emory University analyzed a wealth of past studies using oxytocin nasal sprays, he found that they are very statistically underpowered.”

Much more complex

Once again, a long-held and widely popular belief about human biology — oxytocin is nature’s love glue! — turns out to be, well, far too simplistic.

The hormone’s effects on human behavior are much more complex — and subtle — than its many nicknames suggest. Furthermore, oxytocin has a dark side.

“As I’ve reported before,” writes Yong, “the hormone is highly contextual in its influence. It can trigger positive behavior in some settings, but negative ones like distrust, favoritism, envy, and schadenfreude in others. Biologically, this makes sense. Experimentally, it’s a pain in the ass."

“If scientists blindly run experiments, by complete chance, they’ll find some condition in which oxytocin seems to be doing something — perhaps only in men, or in anxious people, or in anxious men,” he adds. “This is the sharpshooter fallacy, named after an imaginary Texan gunman who fires many rounds at the side of a barn and then paints a target around the biggest cluster of holes.”

Doing the hard science

“Rather than searching for cute, TED-friendly psychological effects,” writes Yong, some scientists have turned their attention to “the hard neuroscience of oxytocin, and [to] working out exactly what this hormone does in the brain.”

Yong details several of the discoveries that have evolved from this research, including the finding that oxytocin “improves the clarity of signals in the brain, by reducing the background buzz of neurons and causing those that fire to do so more sharply.” Other neuoscientists, Yong adds, have demonstrated in mice that oxytocin “tunes the brains of mother mice to the cries of their pups, by acting on regions involved in hearing.”

These and other findings “support the growing idea that oxytocin makes animals pay more attention to social information … like the call of a youngster or the smell of a stranger,” says Yong.

Such an ambiguous message does not lend itself to a snappy, entertaining title for a self-help book or a TED talk.

A yet-to-be-solved mystery

Nor will it sell many supplements — or prescriptions medicines, for that matter. Researchers have already been testing oxytocin inhalants on children with autism to see if it would make them more socially responsive. The results have been mixed. Sometimes it seems to help; other times, it doesn’t.

“These differences probably reflect the hormone’s contextual nature, which becomes incredibly important when thinking about how to use it,” writes Yong.

“This is why the neuroscience of oxytocin is so important,” he stresses. “The inaccurately named ‘moral molecule’ is still more of a mystery molecule, despite decades of work. And that mystery needs to be solved before it finds its way into the clinic.”

You can read Yong’s article on The Atlantic’s website.

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