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Phewee! Can your contraceptive pill change the way a man smells to you – and make you fall out of love?

August 13th, 2008

Dr Petra

Are you falling out of love with your partner? Do you think you’re stuck with a second-rate lover? If so some scientists say you should blame it on your contraceptive pill.

According to new research published in the Proceedings of the Royal Society the use of oral contraceptives could lead to women’s sense of smell being disrupted and as a result their picking mates who are too similar to them – with apparent associated risks to fertility.

Predictably the papers have been all over this story with interpretations of the research that include claims the pill is responsible for couples splitting up, makes women pick ‘Mr Wrong’, will increase your risk of miscarriage, make it difficult for you to conceive, and weaken your immune system. Many papers took this as a signal to encourage women to stop taking the pill immediately.

You can’t really blame the press though. That’s exactly what the press release from the journal said – you can read it here. The only thing the press release didn’t recommend was telling women to stop taking the pill. But if you claim the pill causes women to form relationships that lead to everything from bad relationships to miscarriage or birth defects you can hardly be surprised if the papers jump to the inevitable conclusion that the pill is bad.

Sadly as we all know too well, journalists who are sent press releases rarely bother to read original papers. Which is a shame because as we also know when you go to the original text you can often find the research doesn’t quite live up to the hype of a press release.

The research from the Proceedings of the Royal Society can be found here. The paper is called ‘MHC-correlated odour preferences in humans and the use of oral contraceptives’. While the paper does raise some interesting hypotheses about the possible effects of the contraceptive pill, what it doesn’t do is clearly indicate the pill is as dangerous as the press release indicates.

As an exercise I’d recommend you read the paper (linked above) then revisit the press release (also linked above). You may notice the press release is a lot more gung-ho than the paper. And that’s worrying.

If you don’t have time to read the original paper allow me to summarise. The study involved asking 193 female staff and students at Newcastle University to participate in a study (it does not state how the study was introduced to participants or what they were told it was for). Of those women 97 agreed to take part in the research. 60 were control participants who were not using any form of hormonal contraception at the time of study and 37 were considering taking the contraceptive pill (36 were on the combined pill, 1 was taking the progesterone only pill). It isn’t completely clear from the paper whether the women were put on the pill for the purpose of the experiment, but the paper seems to suggest this. There were some changes to the sample with some women added/excluded from aspects of the research/analysis (see the participants section of the paper linked above for specifics on this).

Alongside the women in the study an additional 97 heterosexual non-smoking male students and staff who were required to wear a prewashed white cotton t-shirt to bed for two nights. The shirts were then given to researchers who cut them in half, and froze them. A number of additional instructions (see ‘odour collection’ section of paper) were also given to men to ensure the t-shirts smelled as much of their scent as possible.

The researchers then selected t-shirts from three men who were similar and three different men to them and required the women to sniff jars containing samples of the defrosted t-shirts and rate them in terms of odour pleasantness, potency and desirability. They did this at four different points over a 90 day period.

Analysis of women’s ratings of the scented samples suggested those not taking the pill were more likely to express a preference for men who were genetically different to them while those on the pill seemed to be less likely to do this.

The paper is not particularly easy to follow. It’s quite dense and contains a fair amount of statistical analysis to wade through. This doesn’t make it a bad piece of work, but it does make it tricky to pick through – particularly if you’re not familiar with how to read a scientific paper (i.e. your average journalists and members of the public).

I spotted a few areas where I’d have liked to have more information. For example, the researchers excluded women who were using other methods of contraception – for example the IUD or injection. Without comparisions with other forms of contraception it’s not entirely possible to conclude the results of this study can be attributed to the contraceptive pill alone. Moreover the paper does not explain what brands of pill the female participants were taking. It is not clear if they were all put on the same brand or were on different brands. Being on the same brand could confound the study since it might be that specific brand that caused the study outcome rather than ‘the pill’ itself (it’s worth remembering there are lots of different contraceptive pills on the market all of which have slightly varying side-effects). It’s also not clear where the pills were obtained from – whether they were delivered by the research team or obtained by the women independently.

Given the amount of press coverage you’d be excused for thinking this is a very large scale study of contraceptive useage, but the data is based on a small-scale sample of not very representative volunteer participants. The researchers themselves make it very clear the study is limited with statements such as: “We do not know whether the change in preferences related to pill use is sufficiently strong to influence partner choice, but it could do so if odour plays a significant role in actual human mate choice”.

This is a long way from strong statements that the pill causes birth defects, miscarriage and relationship breakdown as claimed in the press release. What the paper concludes is that, based on a small and self-selecting sample, the pill might influence partner choice but only if odour plays a role.

Now it would be easy to blame the researchers here, but I don’t think that’s quite fair. The fault clearly lies with the journal who wrote a press release that bounded way beyond the analysis and conclusions presented in what is an interesting but speculative piece of small-scale research. It’s not a bad study, in fact it raises some interesting questions about hormones and attraction, but the way it’s been spun could be very dangerous indeed.

We’ve seen previous studies claim the pill ruins your sex drive, now this research seems to be warning women away from the pill in case they pick the wrong partner or end up having fertility problems. At best this could encourage couples to blame their rows, poor sex life or general unhappiness with each other on the pill rather than other factors, but at worst media coverage of studies of this kind could lead to women abandoning a form of contraception that may suit them perfectly and experience problems (including unwanted pregnancy) as a result.

The message to all women and their partners is do NOT stop taking your pill because you’ve been scared by the coverage of this story in the papers. If you are at all worried speak to whoever prescribes your pill (your GP or someone at your local family planning/reproductive health clinic).

It’s a shame that a study that could have given us some interesting food for thought has been transformed into something more worrying. The journal is to blame for an irresponsible press release and journalists who covered the story are to blame for not tracking down and reading the (freely available) paper.

The irony here is a study that claims the pill possibly could have a negative impact on your relationship and cause fertility problems is very likely to become a self-fulfilling prophecy – and without anyone having to sniff a t-shirt in the process. After all if you read the scary headlines today you can hardly be blamed for chucking your pills out tonight.

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