The first hormonal contraceptive (“the pill”) was approved by the US Food and Drug Administration in 1960.

Since then, hormonal contraceptives have become one of the most prescribed drugs in the world, used daily by more than 100 million people worldwide.

These drugs prevent pregnancy by releasing synthetic hormones into the bloodstream. Synthetic hormones stop the body’s own hormones from stimulating ovulation, so no eggs are released, fertilization cannot occur, and pregnancy is prevented.

Research has shown that natural hormones have a strong influence on the behavior of humans and other animals. But less is known about the behavioral effects of synthetic hormones – like those in the pill.

Some of the hormones affected by the pill are linked to competitive behavior. We wanted to find out more about how hormonal contraceptives change this behavior, so we reviewed all the research we could find about hormonal contraceptives and competitive behavior.

Hormones and competition

Competition is a part of life. We compete for a variety of resources, such as money, food, mates, and allies, to meet our needs and improve our chances of survival and flourishing.

These resources can also be intangible things, such as social status, that give us access to more direct goods. A high-status individual may have better opportunities for education and work, for example.

Hormonal contraceptives directly affect three hormones that have been linked to competitive behavior: testosterone, progesterone, and a type of estrogen called estradiol.

To understand the role of hormonal contraceptives in competition, we reviewed 46 studies, with a total of 16,290 participants. This was all available published research that included a measure of competition.

Status and motivation

One finding from our review was that hormonal contraceptives may have an impact on women’s motivation and ability to achieve higher status.

One study shows an effect of lower achievement motivation.

Another study shows lower performance on tasks that require persistence. This is troubling because people often achieve higher status by demonstrating skill or mastery.

Mating choices

The pill can also affect competition around mating. Recent research shows that women who ride bicycles feel more sexually desirable and attractive mid-cycle, but users of hormonal contraceptives do not.

This suggests that hormonal contraceptives reduce a fertility-induced increase in feelings of desirability that are likely to motivate sexual behavior.

We found no strong evidence that users of hormonal contraceptives differ from non-users in the type of men who withdraw. There was also a lack of evidence that users behave differently when competing for financial resources compared to non-users.

Interestingly, the effect of hormonal contraceptives on mating and status-based competition depended on the relationship status of the participants. For example, one study found that hormonal contraceptive use reduced self-reported competitiveness for women in relationships, but not for single women.

This may mean that synthetic hormones affect single and partnered women differently. On the other hand, it could also mean that single and partnered women have other differences that influence these behaviors.

Small effect sizes and methodological limitations

It is important to note that the differences in behavior between those using hormonal contraceptives and those not using them were generally quite small.

Another finding from our review was that most existing research on the effect of hormonal contraceptives is plagued by significant methodological limitations.

Only one of the studies we reviewed used randomized controlled trials, the gold standard for determining the effect of a particular drug or treatment.

Many of the studies we reviewed also did not take into account other differences between users and non-users of hormonal contraceptives, such as age. These are factors that may explain changes in behavior, independent of hormones and hormonal contraceptives.

Small sample sizes in much of the research make it difficult to generalize to a wider population. In particular, non-white women were largely underrepresented in this research.

Many of the studies also did not report the types of hormonal contraceptives people were using. This makes it impossible to determine whether all types of contraceptives are associated with similar results.

Because of these limitations, the findings in our review are only preliminary.

From here?

Despite 60 years of widespread use, the effects of hormonal contraceptives are still not well understood. They are also used for many purposes other than birth control, such as to reduce premenstrual symptoms, resolve hormone imbalances, or lessen the symptoms of acne and endometriosis.

Access to reliable contraception has huge benefits for individuals and society. It is associated with increased female participation in higher education, a smaller gender wage gap, and reduced female poverty.

To ensure that women can make informed decisions about their bodies, we need reliable and strong evidence about the full effects of hormonal contraceptives.

To paraphrase American filmmaker Sindha Agha, we have the right to birth control, but we also have the right to better birth control. Much more research will be needed.Conversation

Lindsie Arthur, PhD Candidate, Melbourne School of Psychological Sciences, University of Melbourne; Kathleen Casto, Assistant Professor of Psychology, New College of Florida and Khandis R Blake, Lecturer in Psychology, University of Melbourne

This article is republished from The Conversation under a Creative Commons license. Read the original article.

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