The best birth control is easy to use and effective, but nearly all of these medications can come with side effects. The Depo-Provera shot, an effective, discreet and easy to use hormonal birth control method that requires a shot once every three months, causes one in particular: Significant weight gain for about 25 percent of the women who use it.
Back in 2009, a large study showed that Depo-Provera was linked to an average weight gain of 11 pounds across all users over three years. However, this was concentrated in only a quarter of the women who used the shot, meaning that the average amount that this subgroup gained was significantly higher.
In a new pilot study of eight healthy women, researchers set out to find out why this occurs. They discovered that the shot led to heightened activity in the parts of the brain that are linked to food cravings, making it harder for women on the medication to resist junk food.
In the course of the study, the women who received the Depo-Provera shot had more activity in parts of the brain that govern appetite when looking at delicious high-calorie foods compared to baseline measurements that were taken before they received the shot.
If these results are confirmed in more wide-ranging studies, it could be that there’s a neural explanation, not a metabolic one, for why some women gain weight on the Depo-Provera shot. The researchers hope that this discovery may also provide women and their healthcare providers with more tools to avoid weight gain while using the birth control method.
What we knew before:
Women who have had the Depo-Provera shot, a contraceptive that lasts for three months and is administered by a healthcare provider, sometimes complain that they gain weight afterward.
Previous studies have tried to understand the mechanisms behind this Depo-linked weight gain, but have come up short. A 2001 study that measured women’s food intake and resting energy expenditure before and after getting the shot found that women’s metabolisms did not change or slow down after getting the Depo-Provera shot.
The study details:
Researchers recruited eight healthy women, aged 18 to 37, who wanted to get on the Depo-Provera shot. To establish baseline measurements, the researchers drew blood from women, weighed them, assessed total body fat and gave them an fMRI brain scan while showing them pictures of food (both high- and low-calorie items) and non-edible objects. These high-calorie foods included cheeseburgers, pasta, ice cream sundaes, candy and chicken wings. Photos of low calorie foods were things like salads and fruits. The non-edible objects were things like bikes, baskets and rocks.
Then they gave them a shot of Depo-Provera.
Eight weeks later, the participants returned to give all the same measurements and view the same images again while getting fMRI scans. The researchers found that there was no significant change in participants when it came to weight, BMI, body fat percentage or hormone levels related to hunger and fullness (ghrelin and leptin, respectively).
But they did notice a change in the fMRI scans. When viewing the high-calorie foods, there was significantly more blood flow to parts of the brain that govern appetite, food desire, motivation and inhibition -- all parts of the brain that have to do with food cravings. This blood flow was significantly higher than both the participants’ baseline measurements and brain activity levels when viewing low-calorie food or non-edible objects.
What the researcher says:
It’s important to note that this is a very small pilot study of just a handful of women. However, Dr. Penina Segall-Gutierrez, senior author of the study and an associate professor of obstetrics and gynecology at USC, is excited about the possibility for future research on how to mitigate weight gain while on Depo-Provera, as well as a wider understanding of how being on different kinds of hormonal birth control can affect women's brains.
“We’re starting to understand how and why some people gain weight on Depo-Provera as a birth control method,” said Segall-Gutierrez.
Knowing the mechanisms behind the link between the Depo-Provera shot and weight gain could help women be more prepared when they get it, she said.
“This preliminary study really does have the potential to help people who want to use [Depo-Provera] as a birth control method to be able to use it successfully and not gain weight,” said Segall-Gutierrez. “Just as there are behavioral interventions to prevent other diseases, we can tell people hey, you might be more hungry when you’re on Depo."
How this could affect you:
For women who want to use the Depo-Provera shot now, Segall-Gutierrez says they should have a conversation with their doctors about the risks of weight gain and how to avoid it. Now that there is preliminary evidence that the birth control method might have an effect on the brain, doctors can offer more insight beyond the fact that Depo-Provera does not affect metabolism, she said.
"There’s the potential out there that we’ll be able to mitigate the weight gain through anticipatory guidance and just letting people know what to expect," she concluded.
Pfizer, the makers of the Depo-Provera shot, did not immediately respond to a request for comment.