Birth control pills are among the most effective ways to prevent pregnancy, but only if women faithfully take them every day. Human nature being what it is, nearly half of women admit to missing a pill at least once every three months, and, as a result, about 9% of women on oral contraception become pregnant every year.

That number would almost certainly fall if women only had to remember to take the pill once a month or so. That’s why researchers at MIT and Brigham and Women’s Hospital (with support from the Gates Foundation) are trying to create a once-a-month birth control pill.

In a paper published today (Dec. 4) in Science Translational Medicine, a team led by Robert Langer, who runs one of the world’s largest chemical engineering labs at MIT, and Dr. Giovanni Traverso, a gastroenterologist at Brigham and Women’s Hospital and assistant professor of mechanical engineering at MIT, report on a polymer they designed to survive in the harsh, acidic environment of the human stomach for about 30 days. They loaded that polymer with levonorgestrel, a progestin, which is one of the common components that make up popular birth control pills. In a test with pigs, they found that the monthly pill released about the same amount of levonorgestrel in the blood each day as a daily pill.

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