This article was originally published in 2023 and most recently updated on August 12, 2026, with current information.
Some travelers prefer a single long, nonstop flight. Others would rather break up a lengthy trip. No matter what camp you’re in, deep vein thrombosis (DVT)—blood clots, typically in the legs—is a real risk associated with long flights.
“Four hours is the criteria [for DVT], but the more significant risk is at eight hours or longer,” says Harvard Medical School professor Dr. Lin Chen, former director of the Travel Medicine Center at Mount Auburn Hospital in Cambridge, Massachusetts.
The threat of DVT is enough to make some travelers think about taking aspirin, known for its blood-thinning properties, before a flight. But health authorities like the U.S. Centers for Disease Control and Prevention and the U.K.'s National Health Service don’t advise doing so. Here’s what doctors recommend instead of taking aspirin to prevent deep vein thrombosis on long flights.
What causes deep vein thrombosis on flights?
Flight-related DVT is believed to be caused primarily by lack of mobility—a concern considering how much legroom on planes has decreased over the years, especially in economy. These blood clots can travel to the lungs and cause life-threatening blockages known as pulmonary embolisms.
“Our veins work differently from our arteries,” Dr. Danielle R. Bajakian, a vascular surgeon at New York-Presbyterian/Columbia University Irving Medical Center and director of the Critical Limb Ischemia Program at Columbia, told Afar. “While the heart helps drive blood through the arteries, veins rely heavily on movement—especially the calf muscles—to push blood back toward the heart. When we’re immobile for long periods, blood can pool in the veins, which may increase the risk of developing a clot.”
Dr. Bajakian, who notes that the chances of developing blood clots after a long flight are considered to be roughly one in 5,000, describes another possible contributor to DVT: “There’s a theory that with differential air pressure in the airplane [the difference between air pressure inside and outside the cabin], there’s decreased oxygenation of blood, and that, in theory, can also increase the risk of blood clots.”
A January 2025 report from the American Heart Association backs up that idea, stating that “the lower oxygen levels and reduced pressure at high altitudes further contribute to deep vein thrombosis development.”
In addition, the CDC asserts that individual factors may increase the risk of DVT, including obesity, being over the age of 40, recent orthopedic surgery, pregnancy, increased estrogen (including use of birth control or hormone replacement therapy), active cancer, and a prior history of DVT.
Related: 5 Easy Ways to Make Your Economy Flight More Comfortable
Can taking an aspirin before a long flight prevent blood clots?
The CDC does not recommend taking aspirin prior to a long flight for the purpose of preventing blood clots. Dr. Alisa Wolberg, PhD, who is linked to the American Society of Hematology and is a pathology and laboratory medicine professor at the UNC School of Medicine, agrees. Dr. Wolberg told Afar, “There’s no evidence that taking an aspirin before a flight will prevent DVT, so taking aspirin is not recommended. For long flights, move and stretch your legs in your seat, get up and walk periodically (if it’s safe to do so), and stay hydrated. The overall risk of DVT is still fairly low.”
Both Drs. Bajakian and Chen say there isn’t enough data to suggest that aspirin makes a difference for fliers. The U.K.'s National Health Service concurs, saying, “Aspirin has not been shown to be effective in reducing the risk of traveler’s thrombosis.” Dr. Bajakian says, “There are physicians who may potentially recommend it, and that data is not based on any notable studies. The data comes from the orthopedic literature, where there’s a suggestion that in patients who have had hip surgery, DVT prevention is treated with aspirin. But there’s really no data to suggest that that is something that’s warranted to prevent blood clots in the veins while traveling.”
Dr. Chen says that while she does not encourage travelers to take aspirin prior to long flights, she is not completely against it, so long as the patient doesn’t have any health issues that would make aspirin use dangerous. “If a traveler asks, ‘Should I take aspirin before an upcoming long-haul flight?,’ I would tell them that the guidelines don’t show evidence that it prevents deep vein thrombosis, but if they have no contraindications, no issues with tolerance, if they want to do it, I don’t tell them absolutely not to do it.”
Depending on the person’s risk factors and health history, physicians may recommend a prescription anticoagulant, like injectable low molecular weight heparin or an oral alternative, prior to a long flight, but as with aspirin or any other medication, that’s a preventative measure that should only be pursued under the supervision of a doctor.
How else can fliers prevent blood clots?
The good news is that travelers can minimize their risk of DVT without medication. If you are physically able to, it’s a good idea to walk up and down the aisle; Dr. Bajakian recommends doing so once an hour, if possible. Doing calf exercises in your seat can also be beneficial, which is why Dr. Bajakian suggests storing items in the overhead bins and not under the seat in front of you so that you have as much legroom as possible.
Staying hydrated is important, and avoiding sedatives that may keep you in your seat can also help. The CDC, American College of Chest Physicians, and American Society of Hematology all recommend compression socks for travelers with higher risk of DVT in particular, and in general compression socks have been shown to improve blood flow to your heart, writes the Cleveland Clinic.
While these measures are typically offered to travelers with higher risk of DVT, Dr. Bajakian says, “I really recommend them for anybody who’s going to be on a long plane flight.”
