21 October,2010 06:47 PM IST | | Agencies
Sex hormones in the contraceptive pill makes a woman more possessive and more likely to fret about her husband or boyfriend's fidelity.
Those taking brands with the highest levels of oestrogen may even find their hormone-driven suspicions place their relationship in jeopardy, researchers have warned.
The finding is one in a long line of 'emotional' side-effects attributed to the pill, which is taken by some 3.5 million British women, a quarter of all 16 to 49-year-olds.
The drug is also credited with making women broody, changing their taste in men and even boosting intelligence, reports the Daily Mail.
Working with the Dutch psychologists, Stirling University's Craig Roberts in Britain asked 275 women a series of questions designed to gauge how much they trusted their partner, according to the journal Personality and Individual Differences.
Topics included how they feel when their other half flirts with another woman, whether they were worried that he would leave them for another woman and how possessive they were.
The women, who were aged between 17 and 35, had all been taking various versions of the combined pill, containing synthetic forms of oestrogen and progesterone, for at least three months.
Comparing the brands used with the women's answers revealed a clear link between the drug and envy.
And the higher the dose of oestrogen in the contraceptive, the more likely a woman was to be jealous.
Progesterone, however, was not implicated in jealousy, suggesting that progesterone-only versions of the pill play less havoc with women's emotions.
With previous research suggesting that simply going on the pill heightens jealousy, the researchers said that women should be aware of the phenomenon.
Roberts said: "It seems that women, and perhaps pharmaceutical providers, are not fully aware of the range of potential psychological side-effects associated with pill use and more specifically brand choice."
The chemical imbalance caused by the pill can make women chose more boyish men, like Zac Efron, over more rugged men, such as Sean Connery.
In a previous study, Roberts found that the pill may also alter a sense of smell.
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