If you're a woman of a certain age, you might have considered hormone replacement therapy to restore lost oestrogen and get rid of the annoying symptoms of menopause. But while your doctor will have told you about the health risks of HRT, she'll almost certainly not have mentioned its effects on your desire for sexual variety and your chances of straying from the marital bed.
Oestrogen has a lot to answer for. High circulating levels of the hormone early in a woman's adult life account for curvy hour-glass figures, and other feminine features like big eyes, pert little noses, lustrous hair and smooth skin.
But oestrogen doesn't just affect our bodies; it has a big influence on how competitive and bitchy we are with other women, and it affects what kind of men we're attracted to. Women with high oestrogen levels tend to fancy relatively masculine, dominant men - think Xavier Bardem or Tom Hardy - and these qualities are thought to signify good genes that can be passed on to kids. High-oestrogen, hyper-feminine women are also more likely to become dissatisfied with their partners, more likely to trade-up, and more likely to have affairs. It kind of stands to reason - if you're feminine and attractive then you'll have more options on the table.
But then of course when the oestrogen runs out - when we reach menopause, things slow down and even start to go into reverse. Some women become more masculine in appearance, libido has a habit of going south along with everything else, and we even start preferring slightly more feminine looking men. But that makes sense: When you're not in a position to get pregnant, a good companion becomes more important than good genes.
But what happens then when we start messing with our oestrogen levels by taking synthetic hormones? Research has already demonstrated that women on hormonal contraceptives, aka 'the pill', experience greater jealousy and competitiveness with other women, and that when women change their pill use - either they come off the pill or start using it - they often lose sexual interest in their partners.
So what about HRT use? We know it helps get rid of the hot flushes and mood swings associated with menopause, but does it also change our sexual relationships and who we're attracted to? To find out, a team of researchers led by Sarah Donaldson from Oakland University in Michigan carried out an online survey where they questioned 213 post-menopausal women, 80 of whom were on HRT, about their sexual desires and asked them to pick out pictures of men they felt most attracted to.
The research, to be published later this year in Personality & Individual Differences, found that while overall there was no significant effect of HRT on attraction to masculinity in men, different types of HRT had different effects; women using HRT containing both oestrogen and progesterone (vs those using oestrogen-only HRT) reported desiring more masculine and more dominant men compared to their current partner.
And when it comes to sexual desire, previous research already shows an increase in sex drive and more orgasms for women with HRT. In this new study, although women on HRT have greater relationship satisfaction overall, it also demonstrates that the women taking the hormones not only get more libidinous and sexually satisfied, they become more likely than other women to target their sexual desires and fantasising towards men who aren't their main partner. HRT users also demonstrate a higher sociosexuality - that is, they have a more positive attitude towards sex without commitment.
So, while the partners of menopausal women on HRT might be delighted with the new-found ardour of their women-folk, they might need to keep a look out for her roving eye...
Like I said, oestrogen has a lot to answer for, and if you want to manipulate your levels of this hormone, beware the relationship implications - be they good or bad.
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A version of this post first appeared at Sexy Science.