Headache on the way to Mars? Will your aspirin still work?

As NASA scientists contemplate longer space exploration trips, like the projected three-year journey to Mars, they'll have to figure out a lot of logistics that aren't exactly rocket science. That includes what happens if an astronaut gets a headache, a cold or, perish the thought, the runs.

Most pharmaceutical drugs have a shelf life of 12 to 60 months, but experts have wondered whether medicines will degrade faster in space due to microgravity or elevated radiation levels.

"We may not have the opportunity for resupply," said Virginia Wotring, assistant professor in the Center for Space Medicine and Department of Pharmacology at Baylor College of Medicine. "Everything you will need you have to take with you and you have to make sure it's going to work properly after sitting around all that time."

While working at the Johnson Space Center, Wotring learned when the medicines on the International Space Station were due to expire and be replaced. Wotring arranged to have the expired drugs brought back to Earth in the SpaceX Dragon capsule. She tested nine medications — two sleep aids, an antihistamine, a decongestant, three pain relievers, an anti-diarrheal and an alertness medication -- for potency and signs of degradation. Eight of the nine drugs passed muster. Only melatonin pills, a dietary supplement used to promote sleep, degraded beyond an acceptable limit.

The study was funded by NASA's Human Research Program and was published in the AAPS Journal, the official journal of the American Association of Pharmaceutical Scientists.

Wotring was unable to compare how much the same medications would have degraded on Earth over the same time. A 2011 study that compared storage of drugs in space and Earth found that the active ingredients in drugs degraded faster in space.

"Astronauts are healthy people, so they're not using a whole lot of medicines," she said. "Mostly, they're using medications for things related to unusual circumstances imposed by their mission environment."

In a paper published in July, Wotring examined medication records from 24 crew members on 20 missions aboard the ISS. The astronauts primarily used drugs for pain, congestion, allergy and sleep problems. Spacewalks also took a toll on the astronauts, leading to more use of pain medications, and the crew took sleep medications about 10 times more often than they did on earth.

"They're not seeing a sunrise and sunset every day. They're not experiencing the way it's warmer during the daytime and cooler at night, They're missing circadian cues," Wotring said. "We think they honestly have trouble falling asleep because they're locked up in their space bag."

That mirrors the findings of an analysis published last year that found that astronauts on the space shuttle and ISS missions had a lot of trouble sleeping. Some 78 percent of shuttle crew members and 75 percent of ISS crew reporting using sleep aids during their missions.

Wotring is working with scientists at the Johnson Space Center to design experiments that would test the shelf-life of medications in space for longer missions. Because of the rigorous drug testing and approval process, space missions would likely have to rely on formulations chosen by drug companies for earthly markets. But even among common drugs, there are differences in formulation. A 2009 study, for example, tested how well ibuprofen formulations from different manufacturers in different countries held up. That study found wildly different shelf-lives, related primarily to the inactive ingredients used to make the pills.

Wotring is also working on a NASA-funded study that will test how drugs are absorbed, metabolized and excreted by astronauts in space, and whether there is any difference in how well they work in that environment.