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Study debunks theory that a hormone causes men’s refractory period after sex

No matter how high their libidos, most men simply can’t have sex a second time after having an orgasm without a bit of a break, and that’s long been blamed on a pesky hormone called prolactin.

There are even (non-FDA-approved) treatments to that claim shorten the so-called ‘refractory period’ by reducing levels of this hormones.

But a new study brings bad news for men who thought they’d found the secret to a second round: prolactin may not be the problem after all, a new study in mice suggests.

Researchers at the Champalimaud Centre for the Unknown in Portugal found that neither boosting nor cutting prolactin levels in mice of several different species changed their typical refractory periods.

Alternative theories suggest hormones and feel-good hormones like oxytocin, serotonin and dopamine are involved, scientists still don’t know what causes the male refractory period or how to shorten it – and now the most promising explanation seems to be falling  flat.

While women can have sex multiple times in a row and even orgasm multiple times n a row, the vast majority of men have to wait some period of time before they can be aroused enough for sex or orgasm.

It’s long been assumed that a spike in the hormone prolactin causes men’s post-sex refractory period – but new Portuguese study suggests that the hormone has nothing to do with the wait for round two (file)

That changes with age, as well as other factors like stress levels.

Refractory periods for 18-year-old men only last about 15 minutes on average, while a man in his 70s will likely need all day – about 20 hours – before he’s ready to go again.

Why men have to wait has never been fully worked out.

But decades ago, scientists noticed a common theme among male humans and animals who had post-orgasm refractory periods.

In men and other mammals, the hormone prolactin spiked right around the time of ejaculation.

Plus, men with generally low sex drives, who struggle to orgasm or to ejaculate also have chronically high levels of prolactin.

In the absence of a better explanation, the link became cultural cannon.

‘These different results all point towards a central role for prolactin in suppressing male sexual behavior,’ said Dr Susana Lima, corresponding author of the new research, which was published Monday in the journal, Nature.


Like most hormones, prolactin serves a number of roles in male and female mammals.

But its primary function is to help females produce milk to feed their offspring.

It also encourages the development of women’s breasts when they go through puberty.

In men, its role is less clear, and not cyclical, but it’s thought to be involved in sexual arousal and function.

Generally, it exists in low levels in both men’s and women’s bodies.

Women with unusually high levels of it may struggle to conceive or lactate when they are not pregnant.

Men with too much of the hormone may have low sex drives, struggle to keep erections or to orgasm.

If the condition is left untreated too long in men, their sperm production may decline to zero.

‘However, a direct link between prolactin and the male post-ejaculatory refractory period was never directly demonstrated. Still, this theory has become so widespread that it now appears in textbooks as well as in the popular press.’

Like most hormones, prolactin serves a number of roles in male and female mammals, but its primary function is to help females produce milk to feed their offspring.  In men, its role is less clear, and not cyclical, but it’s thought to be involved in sexual arousal and function.

Dr Lima and her team were simply interested in learning more about its role and function and, since mice have refractory periods analogous to those of humans – prolactin spike and all – decided to tweak the animals’ prolactin levels to see whether they became more or less ready to go again.

They boosted prolactin levels in various breeds of mice, expecting them to be totally turned off.

But the mice were unfazed. Those with short refractory periods were still ready to go again shortly after, while those who were slow to get going again still needed about the same amount of time.

Turning down prolactin levels didn’t do anything noticeable to their refractory periods either.

‘If prolactin was indeed necessary for the refectory period, males without prolactin should have regained sexual activity after ejaculation faster than controls,’ lead study author Susana Valente pointed out.

‘But they did not.’

‘Our results indicate that prolactin is very unlikely to be the cause’, said Dr Lima.

‘Now we can move on and try to find out what’s really happening.’

Sex is complicated – and that holds true for the biological processes happening inside our bodies through every stage of sex, from flirtation to how we feel after the deed is done.

In the biological sense, arousal is the result of a complex set of physiological, sensory, chemical, psychological and neurological processes.

Scientists think any or all of these factors could be at play in the male refractory period – but the study suggests a move away from prolactin as a target for ways to shorten than period.

There are no FDA-approved therapies for altering the refractory period, though there is some evidence that erectile dysfunction drugs like Viagra may shorten it somewhat.

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