Most female astronauts choose to skip their periods entirely while in space, using hormonal methods to suppress menstruation for the duration of their missions. This isn’t a medical requirement. Periods work normally in microgravity, and some astronauts have menstruated in space without any problems. But suppression is simpler, and for long missions, it avoids real logistical headaches.
Periods Work Normally in Space
When NASA began selecting female astronauts in the late 1970s, male engineers worried that microgravity might cause menstrual blood to flow backward into the body instead of out. The female astronauts themselves were not worried. They expected a period in space to work the same as on Earth and wanted to treat it as a non-issue unless it became one.
They were right. It’s not clear who was the first woman to menstruate in orbit, but the answer came back exactly as predicted: a period in space is the same as a period on the ground. Menstrual fluid leaves the body the same way it does on Earth. Gravity plays almost no role in that process, since uterine contractions and the body’s own mechanics handle it.
This was a quiet but important moment. A 1964 NASA report had questioned whether menstrual cycles would affect a woman’s ability to operate a spacecraft, suggesting flights might need to be timed around a woman’s cycle. The actual experience of female astronauts made those concerns look exactly as absurd as they were.
Why Most Astronauts Suppress Menstruation Anyway
Even though periods are perfectly manageable in space, most female astronauts on long missions opt for hormonal suppression. The reasons are practical, not medical.
Tampons and pads take up cargo space on a vehicle where every gram is budgeted. They also create waste that has to be stored or disposed of. On a six-month stay aboard the International Space Station, that adds up. For a potential three-year Mars mission, the volume of menstrual products alone becomes a real supply chain problem. Beyond logistics, dealing with personal hygiene in a cramped environment with limited water and no laundry facilities is just easier without a monthly period. Hormonal suppression also helps some astronauts manage cramps, bloating, and the symptoms of gynecological conditions that could be distracting during demanding work.
How Suppression Works
The most common approach has been continuously taking combined oral contraceptive pills, skipping the placebo week so that no withdrawal bleed occurs. This is the same method millions of people use on Earth to skip periods, and it’s well established as safe.
But daily pills have drawbacks in space. Each pill is a small piece of cargo that has to be launched, stored, and eventually discarded. For a three-year deep-space mission, that’s over a thousand pills per astronaut. Medications can also degrade faster in the space environment due to radiation exposure, raising questions about whether pills would remain effective for the full duration of a long mission.
That’s why researchers have increasingly looked at long-acting options. A hormonal IUD lasts up to five years and requires no daily action, no resupply, and produces no waste. A subdermal implant (a small rod placed under the skin of the arm) works for at least three years. Either device could be inserted before launch and wouldn’t need replacement during even the longest currently planned missions. Neither one has been shown to negatively affect bone density in premenopausal women on Earth, which matters in space for reasons we’ll get to.
Despite the advantages, long-acting devices haven’t been widely adopted by astronauts yet. There’s no data specifically on how the high G-forces of launch and reentry might affect an implant or IUD, though researchers note that military jet pilots experience similar forces without reported problems. On the rare chance an IUD were expelled during flight, the astronaut would simply begin menstruating normally, which wouldn’t prevent her from doing her job.
The Bone Density Question
Astronauts lose bone at a much higher rate than people on Earth. Microgravity removes the mechanical loading that keeps bones strong, and some of that loss is irreversible. This creates a unique concern around certain hormonal methods.
On Earth, the progestin-only injection (given every three months) is associated with temporary reductions in bone mineral density. Those losses reverse after stopping the injection. But in space, where bone loss from microgravity may not fully recover, stacking a medication that also reduces bone density could be a real problem. For that reason, the injection is generally not the preferred option for spaceflight.
Combined oral contraceptive pills contain estrogen, which typically supports bone health. But no one has studied whether taking them continuously in microgravity actually protects against bone loss, or whether the combination of the pill and weightlessness creates unexpected effects. NASA’s 2023 Decadal Survey flagged this as a key research area for the coming decade. The hormonal IUD and subdermal implant appear safer on this front, since neither has been linked to bone density changes in premenopausal women.
What About Water Recycling?
The ISS recycles nearly everything. The Water Recovery and Management system processes urine, humidity from the air, and hygiene wastewater back into drinkable water. If an astronaut menstruates, any menstrual fluid that enters the waste stream would be processed through these systems.
This isn’t a dealbreaker, but the recycling hardware is already finicky. The urine processor has struggled with mineral buildup and corrosion. The water processor needs its filters replaced more often than planned due to contaminants it can’t fully remove. Adding another variable to an already stressed system is one more reason suppression tends to be the simpler path.
Choice, Not Mandate
Nothing about spaceflight policy requires female astronauts to suppress their periods. NASA’s medical guidelines list hormonal options including oral contraceptives, progesterone IUDs, and other hormonal treatments as available tools, but the decision belongs to the astronaut. Some women have chosen to menstruate in space on previous flights, though detailed data from those experiences is limited since it hasn’t been a focus of formal study.
That gap in knowledge is itself a problem. Researchers have pointed out that hormonal suppression doesn’t serve astronauts who simply prefer to menstruate, and that the space medicine community still knows relatively little about how the full menstrual cycle interacts with the spaceflight environment. Recent studies have also raised concerns about whether combined hormonal contraceptives might increase the risk of blood clots in space, where fluid shifts and reduced physical activity already push clotting risk higher. For now, most female astronauts choose suppression because the practical benefits are clear and the alternatives are inconvenient. But as crews grow larger and missions grow longer, the range of options and the research behind them will need to catch up.