London - Women could soon need to take the Pill only once a month instead of every day, scientists say.
They have designed an oral contraceptive tablet that can remain in the stomach for three to four weeks, during which time it releases its drugs.
The monthly pill could be available within three to five years, according to researchers. This could reduce unwanted pregnancies that result from women forgetting to take a daily dose.
Oral contraceptives are one of the most popular forms of birth control, but to work they need to be taken daily. An estimated one in 11 women taking birth control pills become pregnant each year.
Researchers at Massachusetts Institute of Technology (MIT) in the US said the breakthrough may have a "significant impact" on the health of women and their families, especially in the developing world. The slow-release drug system could also work for other conditions such as HIV and malaria.
Study co-senior author Dr Giovanni Traverso said: "Our capsule represents a major advancement toward providing women with a once-a-month contraceptive. For many, this may be hard to believe. But our pre-clinical data is encouraging us along that road.
"We began our work on extended drug release by working with treatments for malaria, tuberculosis and HIV. But early on, we were having conversations about the potential impact extended drug release could have for family planning. We wanted to help empower women with respect to fertility control and are pleased to report our progress toward that goal."
Work is now underway to bring the extended-release pill closer to human trials.
The next steps will include scaling up manufacturing processes and safety evaluations. Co-author Professor Robert Langer said: "We are hopeful this work – the first example ever of a month-long pill or capsule to our knowledge – will someday lead to potentially new modalities and options for women’s health."
The new pill is based on star-shaped drug delivery systems that the team previously developed, which can remain in the digestive tract for days or weeks after.
Once swallowed the pill flips out six arms to make a star shape, which prevents it from exiting the stomach. But by the end of the third or fourth week, it is broken down.
Tests in pigs showed that sort of drug release can achieve the same concentration of the drug in the blood as taking a daily dose.
Much of the work has been funded by the Bill and Melinda Gates Foundation, which urged the team to adapt the capsule for long-lasting contraceptives.
Dr Traverso, an assistant professor of mechanical engineering at MIT, said: "Through the development of these technologies, we aim to transform people’s experience with taking medications by making it easier.
"We’re very committed to getting these technologies to people over the coming years."
The World Health Organisation estimates 214 million women in developing countries who want to avoid pregnancy are not using a modern contraceptive method, such as the Pill. The findings were published in the journal Science Translational Medicine.