Despite decades of advancement in reproductive health, access to effective birth control remains a challenge for millions. Pills require daily discipline and uninterrupted supply. Injections like Depo-Provera only last three months, requiring regular clinic visits that aren’t feasible for many. Long-acting implants can provide extended protection, but they often require surgical insertion and removal—procedures that aren’t always accessible or affordable.
According to the Guttmacher Institute, more than 214 million women in developing countries who want to avoid pregnancy are not using modern contraception. The reasons are clear: logistical barriers, medical limitations, and the lack of options that fit real-world needs.
A research team at MIT, backed by funding from the Bill and Melinda Gates Foundation, is working on a solution that could change that. Their goal: a single injection that provides long-lasting pregnancy protection—possibly for a year or more—without surgery, large needles, or repeated visits to a clinic.
A New Kind of Shot: What the Gates-Backed Research Has Developed
The solution scientists are developing is called SLIM—short for Self-aggregating Long-acting Injectable Microcrystals. It’s a new approach to birth control that delivers a high dose of contraceptive hormone in a single injection, using a needle small enough for routine vaccinations.
Here’s how it works: instead of relying on thick gels or high volumes of polymer to release the hormone slowly over time, SLIM uses microscopic crystals of levonorgestrel—a well-known contraceptive hormone used in pills and implants. These crystals are suspended in a liquid solvent called benzyl benzoate, which is already used in approved injectable medications.
Once injected just under the skin, the solvent interacts with body fluids in a way that causes the drug crystals to clump together and form a compact depot. This depot stays in place and releases the hormone gradually over time. No implant needed, no thick needle, no surgical procedure.
Dr. Giovanni Traverso, the senior author of the study and a mechanical engineering professor at MIT, put it plainly: “We showed that we can have very controlled, sustained delivery, likely for multiple months and even years through a small needle.”
What makes this different from existing injectables is not just the drug itself, but the delivery system—engineered to be as simple and efficient as possible, with long-term use in mind.
How This Single Injection Could Last for a Year or More
One of the key goals behind SLIM is duration—making contraception last longer without increasing complexity. In animal studies, the early results have been promising. Researchers injected the hormone-crystal suspension into rats and monitored how the drug was released over time. After three months, about 85% of the hormone was still present in the depot, indicating that the formulation could continue working well beyond that point.
Based on these findings, the team believes this single injection could potentially provide pregnancy protection for a year or longer. And because the depot forms under the skin on its own—without implants or surgical placement—it keeps the process simple for patients and providers alike.
Another key advantage is tunability. By adding very small amounts of biodegradable polymer—less than 1.6% by weight—researchers can fine-tune how quickly the hormone is released. This allows flexibility in designing formulations that fit different needs: from shorter-term options to extended coverage that could last well over a year.
The team also confirmed that the drug depot remains retrievable, offering an added layer of safety. If a patient experiences side effects or wants to discontinue early, the depot can be surgically removed without difficulty.
These features—long duration, tunability, and reversibility—are what set this injection apart from anything currently on the market.
Designed for Access: Small Needle, No Surgery, Potential for Self-Use
One of the biggest barriers to long-acting birth control is how it’s delivered. Current injectable contraceptives often require large, thick needles—typically 18 to 20 gauge—which can cause significant pain, bruising, and make self-injection nearly impossible. That discomfort and dependency on clinical settings limit how widely and consistently these options can be used.
SLIM changes that. Because the hormone is suspended in a low-viscosity solvent and doesn’t require bulky polymers, it can be injected using a 25-gauge needle or smaller—about the size used for routine vaccines. That makes the experience significantly less painful and opens the door for self-administration.
In practical terms, this could mean a woman receiving a one-year contraceptive injection at a clinic—or possibly even at home—with a needle so small it barely registers. For people in rural areas, conflict zones, or regions with limited healthcare access, that difference could be the key to consistent family planning.
And since the formulation is stable and composed mostly of the active drug (with minimal added materials), it’s more efficient to produce and doesn’t rely on complex storage conditions. This makes it easier to scale and distribute in low-resource settings.
In short, SLIM was designed not just to work in a lab, but to function in the real world—where comfort, convenience, and autonomy matter just as much as clinical efficacy.
What This Could Mean for Global Contraceptive Access
The Gates Foundation’s involvement signals more than just financial support—it reflects a strategic push to address longstanding gaps in reproductive healthcare, especially in low-income regions. For millions of women, current birth control options are either unavailable, unaffordable, or impractical. A once-a-year injection that’s easy to use and doesn’t require surgery could shift that reality.
Vivian Feig, one of the lead researchers and now a professor at Stanford University, emphasized this broader mission: “The overarching goal is to give women access to a lot of different formats for contraception that are easy to administer, compatible with being used in the developing world, and have a range of different timeframes of durations of action.”
That kind of flexibility is essential. With SLIM, the same delivery technology could eventually be tailored for multiple timelines—six months, one year, or longer—allowing public health systems to choose what works best for their populations.
The potential doesn’t stop at contraception. Because the depot technology is compatible with other drugs, researchers are already exploring applications for HIV prevention, mental health medications, and tuberculosis treatments—all areas where missed doses or access barriers can undermine outcomes.
In short, this isn’t just a new contraceptive. It’s a platform that could make long-acting drug delivery feasible and accessible for some of the most pressing health challenges around the world.
What to Know While Waiting for Long-Lasting Options Like SLIM
Long-acting birth control that works with just one small injection could be a game changer—but it’s not here just yet. In the meantime, there are still reliable ways to manage your reproductive health without feeling overwhelmed by complicated routines or hard-to-access options.
Here are a few things to consider while SLIM technology moves closer to real-world use:
- If daily pills aren’t realistic, ask about longer-term options: Birth control isn’t one-size-fits-all. If remembering a pill every day is difficult, talk to your provider about injectables, IUDs, or implants that last for months or years.
- Be honest about what’s manageable for you: Whether it’s work, travel, or lack of nearby clinics, let your provider know what makes follow-up visits hard. The right method should support your life, not disrupt it.
- Understand how long each method lasts—and how to stop if needed: Some contraceptives are easier to reverse than others. Ask how long it takes for fertility to return and what your options are if you change your mind.
- Stay updated on new developments: Keep an eye on research from institutions like MIT or updates from public health sources. Knowing what’s in the pipeline can help you plan ahead.
- Revisit your method if your needs change: Life shifts—so should your birth control. Whether you’re switching jobs, managing a health issue, or planning a pregnancy down the road, check in with your provider regularly.
There’s no need to wait for the “perfect” option to take control of your health now. But when methods like SLIM do become available, they’ll offer another tool to make contraception more practical, accessible, and on your terms.
A Simpler, Smarter Option on the Horizon
The SLIM injection isn’t available yet, but it’s moving steadily through preclinical development. If successful in human trials, it could offer a safer, more practical alternative to existing long-acting birth control methods—no surgery, no thick needles, and no need for quarterly clinic visits.
What makes this technology stand out is its real-world usability. It’s not just about scientific innovation—it’s about meeting people where they are, especially in parts of the world where reproductive healthcare is difficult to access or maintain. A once-a-year shot that can be self-administered has the potential to redefine contraceptive access globally.
For now, the best thing you can do is stay informed. Follow developments from reliable sources, ask your healthcare provider about new options, and advocate for solutions that prioritize both safety and accessibility.
The future of birth control might look like a small, nearly painless injection—but its impact could be anything but small.
