Effects on weight are the subject of debate

Women who stop taking the pill often do so because they think it has been causing them to gain weight. Clinical studies in this area are contradictory: Some women said that they gained weight, while others reported losing weight. This is why both weight gain and weight loss are listed as possible side effects on the product information of hormonal contraceptives.

If people put on weight it is usually due to one of the following changes:

• Fluid retention
• An increase in muscle tissue (because muscle is heavier than other tissue)
• An increase in body fat

Theoretically, hormonal contraceptives could contribute to weight gain if they led to fluid retention and increased body fat. Also, combined contraceptives are sometimes believed to increase appetite. But it’s not that easy to say whether that’s true because women who don’t use hormonal contraceptives also gain weight as they age.

The research results are uncertain

In order to find out whether the birth control pill actually influences body weight, we would need studies with one group of women who use hormonal contraceptives over a long period of time and another group who do not. Then the groups could be compared to see if there are any differences in their weight.

Researchers from the Cochrane Collaboration looked for such good-quality studies on hormonal contraceptives in which weight was recorded. They were only able to find a few studies that compared hormonal contraceptives with “fake” hormonal contraceptives (placebos) and measured the impact on weight. This is not that surprising, though. Because hormonal contraceptives are so reliable, not many women are willing to use contraceptives that could be less effective or may even be placebos and not work at all.

None of the studies found by the researchers show a clear link between hormonal contraception and weight gain. But these studies did not have enough participants and were not well-designed to be able to provide a definite answer. In addition, most of the studies didn’t record the participants' weight very carefully. At most, only the number of women who reported that they stopped taking the pill because of weight gain was recorded. So it's not possible to say for sure whether the participants who used hormonal contraceptives gained more weight than the women in the other group.

A major effect on weight is unlikely

Because of this, one group of researchers also looked for studies where different combined contraceptives were compared with one another and weight was carefully recorded. They found 45 studies in which many different types of hormonal contraceptives were compared. So it's difficult to tell how the individual types affect weight.

What’s more, no link was found between hormone dosage and weight gain. If hormones really did influence weight gain, then you would expect higher doses to lead to more weight gain. Such a link was not established.

On the whole, the researchers concluded that it seems very unlikely that hormonal contraceptives cause major weight gain. If there were a strong effect, it would have been noticed in the studies. But this doesn't rule out the possibility that individual women could in fact gain weight.

Sources

• Gallo MF, Lopez LM, Grimes DA, Schulz KF, Helmerhorst FM. Combination contraceptives: effects on weight. Cochrane Database Syst Rev 2014; (1): CD003987. [PubMed: 16437470]
• Lopez LM, Ramesh S, Chen M, Edelman A, Otterness C, Trussell J et al. Progestin-only contraceptives: effects on weight. Cochrane Database Syst Rev 2016; (8): CD008815. [PMC free article: PMC5034734] [PubMed: 27567593]

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