Study: No Link Between The Pill and Weight Gain

Many women refuse to go on the Pill out of fear of weight gain, putting themselves at a higher risk for unplanned pregnancy. But new findings on weight gain and oral contraception may put many minds at ease.

According to research conducted at the Oregon National Primate Research Center at Oregon Health & Science University, the commonly held belief that oral contraceptives cause weight gain appears to be false.

"A simple Google search will reveal that contraceptives and the possibility that they may cause weight gain is a very highly debated topic," said Alison Edelman, M.D., a physician and researcher in the Department of Obstetrics and Gynecology at OHSU and lead author of the study.

Edelman said issues surrounding weight are hard to study in humans, and the research thus far has been insufficient to demonstrate whether oral contraceptives cause changes in weight.

“But this is an extremely important question as concern about weight gain is one of the main reasons why women may avoid or discontinue birth control, which in turn places them at greater risk for an unplanned pregnancy," Edelman noted.

Monkey study

To conduct their research, scientists and physicians studied a group of rhesus macaque monkeys for almost a year. The monkeys were studied because their reproductive system is nearly identical to humans, but unlike humans, more variables can be controlled and measured -- such as exact food intake -- to provide more meaningful data.

At the beginning of the study, half the monkeys were obese and half were of normal weight. During the eight-month treatment period, animals received doses of oral contraceptives, adjusted to their weight so that it mimicked dosage in humans.

The researchers tracked weight, food intake, activity levels, body fat and lean muscle mass.

At the study's conclusion, the normal weight group remained weight stable whereas the obese group lost a significant amount of weight (8.5 percent) and percent of body fat (12 percent) due to an increase in basal metabolic rate.

The monkeys’ food intake, activity or lean muscle mass levels did not change during the study -- for either group.

Concerns unfounded

Judy Cameron, Ph.D., senior author of the paper and a researcher at the primate center said the study results suggest worries about weight gain related to using the Pill “appear to be based more on fiction than on fact."

Cameron notes the pill affects women differently depending on their weight. She said some heavier women might actually lose weight when taking the Pill, if they keep their diets stable.

So why is the rumor so prevalent and deeply believed? Cameron thinks it has to do with the fact many young women start to naturally gain weight around the age they start taking the Pill -- and they blame the pill, not their slowing metabolism.

Still, Cameron admits more research on the subject is needed.

“We realize that research in nonhuman primates cannot entirely dismiss the connection between contraceptives and weight gain in humans, but it strongly suggests that women should not be as worried as they previously were," she said.

The results of the study are published online and will appear in next month's edition of the journal Human Reproduction.