When should I see a doctor before an international trip?

4-6 weeks before departure is the window the CDC recommends, because several travel vaccines need series or lead time to protect you, and a yellow fever certificate becomes valid 10 days after vaccination. Fishtown Medicine builds the plan in a phone or video visit and also sees travelers leaving within days, since prescriptions and several vaccines still work on short notice.

Is 1 week before my trip too late for travel medicine?

No. Hepatitis A vaccination protects most healthy adults even when given close to departure, injectable typhoid is a single shot, and malaria pills like atovaquone-proguanil or doxycycline start 1-2 days before you arrive. What no longer fits inside a week is the oral typhoid series and a valid yellow fever certificate, which begins counting 10 days after the shot.

Where do you get the yellow fever vaccine in Philadelphia?

Only at a certified yellow fever vaccination clinic, which is an international rule, and the CDC keeps the registry of certified centers. Philadelphia has certified travel clinics, and Fishtown Medicine points you to one and builds the 10-day certificate window into your timeline. This vaccine cannot be given at a routine medical visit or most pharmacies.

Does Fishtown Medicine give travel vaccines during the visit?

No. Fishtown Medicine visits happen by phone and video, so vaccines are given at a pharmacy near you or, for yellow fever, at a certified travel clinic. The visit decides which vaccines and medicines your itinerary calls for, sends prescriptions to your pharmacy, and maps where and by when each shot happens, with the practice coordinating the yellow fever referral.

Is travel prep different during pregnancy?

Yes. Live vaccines such as oral typhoid and yellow fever are generally avoided in pregnancy, malaria deserves a harder look because infection during pregnancy is more dangerous, and destinations with active Zika transmission matter for pregnancy and pregnancy planning. None of that cancels a trip by default; it means the plan gets built person by person, ideally early.

Do I need travel vaccines for Europe?

Usually no destination-specific ones. For most of Western Europe the job is making sure routine vaccines are current, measles above all, since outbreaks recur there, and the CDC destination page for your specific country confirms it. The prescriptions that matter for a European trip are usually your own medications, packed in original bottles with a buffer supply.

When should I see a doctor before an international trip?

4-6 weeks before departure is the window the CDC recommends, because several travel vaccines need series or lead time to protect you, and a yellow fever certificate becomes valid 10 days after vaccination. Fishtown Medicine builds the plan in a phone or video visit and also sees travelers leaving within days, since prescriptions and several vaccines still work on short notice.

Is 1 week before my trip too late for travel medicine?

No. Hepatitis A vaccination protects most healthy adults even when given close to departure, injectable typhoid is a single shot, and malaria pills like atovaquone-proguanil or doxycycline start 1-2 days before you arrive. What no longer fits inside a week is the oral typhoid series and a valid yellow fever certificate, which begins counting 10 days after the shot.

Where do you get the yellow fever vaccine in Philadelphia?

Only at a certified yellow fever vaccination clinic, which is an international rule, and the CDC keeps the registry of certified centers. Philadelphia has certified travel clinics, and Fishtown Medicine points you to one and builds the 10-day certificate window into your timeline. This vaccine cannot be given at a routine medical visit or most pharmacies.

Does Fishtown Medicine give travel vaccines during the visit?

No. Fishtown Medicine visits happen by phone and video, so vaccines are given at a pharmacy near you or, for yellow fever, at a certified travel clinic. The visit decides which vaccines and medicines your itinerary calls for, sends prescriptions to your pharmacy, and maps where and by when each shot happens, with the practice coordinating the yellow fever referral.

Is travel prep different during pregnancy?

Yes. Live vaccines such as oral typhoid and yellow fever are generally avoided in pregnancy, malaria deserves a harder look because infection during pregnancy is more dangerous, and destinations with active Zika transmission matter for pregnancy and pregnancy planning. None of that cancels a trip by default; it means the plan gets built person by person, ideally early.

Do I need travel vaccines for Europe?

Usually no destination-specific ones. For most of Western Europe the job is making sure routine vaccines are current, measles above all, since outbreaks recur there, and the CDC destination page for your specific country confirms it. The prescriptions that matter for a European trip are usually your own medications, packed in original bottles with a buffer supply.

Travel Medicine Philadelphia | Vaccines and Trip Prep

TL;DR30-second take

Start travel medicine 4-6 weeks before an international trip: destination vaccines like typhoid, hepatitis A, and yellow fever need lead time, and yellow fever is given only at certified clinics. Fishtown Medicine builds the plan in a phone or video visit and sends prescriptions to your pharmacy. Even 1 week out, a visit is still useful.

TL;DR: If you booked a trip to another country, see a doctor about 4-6 weeks before you leave. Some travel shots need that much time to start working. The doctor checks what your destination calls for, updates your regular shots, and sends any medicines to your pharmacy, like malaria pills or an antibiotic for severe stomach illness. Pack every medicine in its original bottle, in your carry-on, with extra in case you get stuck somewhere. If you leave in a week, a visit still helps: several shots work fast, and the pills can start right away. The order: book the visit as soon as the trip is booked, get the shots your destination calls for, fill the prescriptions, and pack the kit in the last week.

The flights are booked, the time off is approved, and somewhere on your list is a vague line that says "shots?" This page turns that line into specifics: what depends on your destination, what depends on you, and when each piece has to happen. An early look usually shrinks the job, because you find out which kind of trip yours is while there is still time to act on the answer.

When should you start getting ready?

About 4-6 weeks before departure, which is the timing the CDC recommends for a pre-travel visit. The window comes from how the pieces work. Several vaccines take 2 weeks or more to build protection. The oral typhoid vaccine is a series spread over a week, finished at least a week before travel. A yellow fever certificate, where a country requires one, only becomes valid 10 days after the shot. A month absorbs those timelines comfortably; less than that starts forcing substitutions.

Starting early also costs nothing if your trip turns out to be simple. A week in London needs a different conversation than a month in rural Cambodia, and an early look tells you quickly which conversation you are in. If your departure is already inside the month, keep reading anyway; the last-minute section below covers what still works, and the list is longer than most people expect.

Which vaccines depend on the destination?

Typhoid, hepatitis A, and yellow fever are the main destination-driven vaccines, and the CDC destination pages are the living list for the specific country you are visiting: pick the country and it shows what is recommended, what is required for entry, and whether malaria is part of the picture. That tool is the same one your doctor should have open during the visit.

Typhoid is a bacterial infection carried by contaminated food and water, common enough across South Asia in particular that vaccination is standard advice there. It comes 2 ways. The injectable vaccine is a single shot, given ideally at least 2 weeks before travel, and protects for about 2 years. The oral version is 4 capsules taken over a week, finished at least 1 week before departure, and protects for about 5 years, which makes it a favorite of frequent travelers; it is a live vaccine, though, so it is not the right form in pregnancy or with a weakened immune system. Timing and preference decide between them, and the decision takes about a minute once the dates are known.

Hepatitis A rides the same food-and-water route and attacks the liver. Its vaccine is forgiving: a single dose given any time before departure protects most healthy adults, and a 2nd dose 6 months later makes the protection long-term. Many adults already had the series as part of routine care, which is one reason the travel visit doubles as a general vaccine check: measles, tetanus, flu, and COVID travel on every itinerary. The adult vaccine schedule guide covers that routine side in full.

Yellow fever is the special case. A number of countries in Africa and South America require proof of vaccination to enter, and the proof is a stamped International Certificate of Vaccination or Prophylaxis, the yellow card, which becomes valid 10 days after the shot. Only certified yellow fever clinics can give this vaccine and issue the certificate, so this one shot happens at a certified center no matter who your doctor is. The CDC keeps a registry of certified clinics, Philadelphia has them, and the practice's job is to point you to one and build the 10-day window into your timeline.

2 more vaccines exist for narrower itineraries, Japanese encephalitis for a month or more in rural parts of Asia and rabies pre-exposure shots for remote destinations far from reliable medical care or trips with planned animal contact, and the destination check is what flags them.

What about malaria?

Whether you need malaria pills depends on the region, and which pill you get depends on you. Malaria is a parasite spread by mosquitoes that bite from dusk onward, it lives in defined parts of the world, and the CDC publishes a country-by-country table of where prevention is recommended and which drugs work there. Plenty of popular destinations need nothing. Others, including much of sub-Saharan Africa, call for prophylaxis on essentially every itinerary.

Where pills are called for, the usual options are atovaquone-proguanil, doxycycline, mefloquine, and tafenoquine, and all of them work when they match the region. The match runs through the itinerary first, because resistance patterns differ by region and rule specific drugs out in specific places, and then through you: your medications, your history, how you feel about a daily pill versus a weekly one, how much sun exposure the trip involves. Some of these start 1-2 days before you enter the malaria area, one starts weeks ahead, and each continues for a set stretch after you leave. That decision belongs in the visit with the country table open, and the prescription goes to your pharmacy the same day.

Pills are half of malaria prevention. The other half is not getting bitten: repellent on skin, permethrin on clothing, screens or a net where you sleep, sleeves after dusk. Those same habits also protect against dengue and the other mosquito-borne infections that have no pill at all.

What is the plan for traveler's diarrhea?

Pack a self-treatment plan, because careful eating helps and cannot do the whole job. The classic rules, cook it, peel it, drink bottled or boiled water, skip the ice, are reasonable, and the evidence behind them is mixed: studies of travelers who follow the rules find that plenty get sick anyway, partly because the restaurant kitchen is outside your control. So follow the precautions where you can, and pack the backup plan for the day they fall short.

The plan has 3 layers, matched to how sick you are. Fluids come first at every level: diarrhea drains water and salt together, and oral rehydration salts, the pharmacy packets you stir into safe water, replace both far better than water alone. Loperamide, the over-the-counter medicine that slows the gut down, handles mild cases well enough to get you through a travel day. For the severe end, fever, blood, or a day you cannot function, the kit carries an antibiotic prescribed before you left. In South and Southeast Asia that antibiotic is usually azithromycin, because resistance to the older quinolone antibiotics is widespread there, above all in Campylobacter, one of the region's common culprits. Which drug, and the threshold for taking it, gets settled in the visit so you are never deciding from scratch at 2am abroad.

Most traveler's diarrhea ends within a few days. A case that follows you home and keeps relapsing for weeks has a different list behind it, including parasites a routine stool test misses; the cyclospora guide covers the one to ask about by name after produce-heavy travel.

What if your trip goes high?

If your itinerary sleeps above about 8,000 feet, roughly 2,500 meters, altitude illness belongs in the plan. Cusco, La Paz, Lhasa, and the trekking towns of the Himalaya all start at or above that line, and the highest-risk pattern is the common one: flying from sea level to a high city in a single afternoon, which gives your body no time to adjust. The usual result is acute mountain sickness, the headache, nausea, and heavy fatigue of a body short on oxygen, and in a small share of people it builds into fluid on the brain or in the lungs, which are emergencies.

Acetazolamide, a medicine that speeds up your body's own acclimatization, prevents acute mountain sickness when started before ascent, and the CDC encourages it for moderate- and high-risk ascent profiles, a category that includes flying directly into cities above 11,000 feet. Itinerary design does as much work as the medicine: ascend gradually when the route allows it, and sleep lower than the day's high point. Because the prevention starts before the climb, this is a pre-trip prescription, and the visit decides whether your route earns it.

3 symptoms at altitude mean descending and getting seen now: a headache that keeps worsening despite rest, fluids, and pain medicine; confusion, clumsiness, or a stumbling walk; and breathlessness at rest or a wet cough. The last 2 are the brain and lung forms of altitude illness, and every form improves with descent.

Do long flights raise the risk of blood clots?

Yes, modestly for everyone, and meaningfully for some people. Staying in a seat for more than about 4 hours slows the blood flow in your leg veins, and slow-moving blood clots more easily. The clot is a deep vein thrombosis, a clot in the deep veins of the leg, and the danger is a piece breaking loose and traveling to the lungs. For most healthy travelers the absolute risk on any single flight stays small, and the countermeasures are free: walk the aisle every 1-2 hours, do ankle circles and calf pumps in your seat, and favor water over alcohol on the way.

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Personal risk changes the conversation. Recent surgery or a hospital stay, a prior clot, pregnancy or the weeks after delivery, estrogen from birth control or hormone therapy, active cancer, obesity, and age past about 40 each raise the baseline, and stacking several of them before a 15-hour flight is a reason to talk before you fly: properly fitted compression stockings cut the rate of symptomless clots in airline trials, and a small group with strong histories needs more than stockings. A swollen, painful calf in the days after a long flight, or sudden breathlessness or chest pain, is emergency care, at home or abroad.

What goes in the kit?

Your everyday prescriptions, the trip-specific ones, and the small items that are hard to find in an unfamiliar pharmacy. The CDC's travel health kit guidance is the long version; this is the core:

Every prescription in its original labeled bottle, in your carry-on. Checked bags miss connections. Bring enough for the whole trip plus a buffer for delays, and carry copies of the prescriptions that name the generic drug.
The trip prescriptions from the visit: malaria pills, the diarrhea antibiotic, acetazolamide when the route goes high.
Oral rehydration salts and loperamide, the first 2 layers of the diarrhea plan.
Insect protection: an EPA-registered repellent with DEET or picaridin for skin, and permethrin spray for clothing and gear before you pack. Permethrin holds through several washes and never goes on skin.
Sun protection: broad-spectrum sunscreen, and a hat you will wear.
The basics: a pain reliever, an antihistamine, bandages, a thermometer, hand sanitizer.

One piece of paper matters as much as the pills. Before you leave, ask your health insurer 2 questions: does my plan cover medical care abroad, and does it cover getting me home? Many US plans cover little outside the country, and Medicare covers close to nothing overseas. A travel health policy that includes medical evacuation coverage is inexpensive next to what it insures; an air evacuation can run into 6 figures. For a beach week in a city with good hospitals it is a judgment call; for a remote itinerary it is close to mandatory.

What if you leave in a week?

See a doctor anyway; the CDC's guidance for last-minute travelers says in as many words that it is never too late for a pre-travel visit, even days before departure. A useful amount survives the compressed timeline. Hepatitis A vaccination protects most healthy adults even when the dose is close to departure. The injectable typhoid shot is a single visit. Malaria pills that start 1-2 days before arrival, atovaquone-proguanil or doxycycline, remain fully on the table. The diarrhea plan, the kit, and the insurance call take an afternoon.

What a week can no longer do: the oral typhoid series needs about 2 weeks of runway, so the injectable takes its place, and a yellow fever certificate only becomes valid 10 days after the shot. If your destination requires one, the certified clinic has to happen this week, and if the math no longer works, that becomes a conversation about the entry requirement before you board. A late visit triages: the 2 or 3 biggest risks of your specific destination get covered first, and the rest gets folded into a plan for next time.

Guidance from the Clinic

"Most trips need a shorter list than people expect. The itinerary decides most of it, so I read that first, and then we keep what your destination and your health call for and skip what would be an expense for no reason."

How does Fishtown Medicine handle travel prep?

The plan gets built in a phone or video visit with Dr. Ash, itinerary open on both ends. He reads the CDC page for your destination with you, weighs it against your health, your medications, and your dates, and turns it into a short list: which vaccines, where each one happens, which prescriptions, and the date each step has to happen by. Prescriptions, malaria pills, the diarrhea antibiotic, acetazolamide when the route climbs, go to your own pharmacy. Fishtown Medicine visits happen by phone and video, so the vaccines themselves are given at the places that stock them: most travel shots at a pharmacy near you, and yellow fever at a certified clinic the practice locates for you, scheduled early enough for the certificate to be valid when you land.

If you carry a long medical history, you do not have to retype it for a trip. Share what you have the energy for in the intake, upload the records you already hold, and once you connect, the practice can request the rest on your behalf; Dr. Ash reads what arrives before the visit, so the conversation starts at your trip. The fastest way to begin is the intake: name the destination, the departure date, and anything about your health that worries you for this trip.

When does travel prep need a doctor now?

3 situations stop being planning and need care the same day.

A fever in a malaria region, or in the weeks and months after coming home from one, is urgent the day it starts. Falciparum malaria can move from flu-like to life-threatening within days, and it is treatable when caught, so a returned-traveler fever needs same-day evaluation, and telling whoever sees you where you traveled is what points them at the right test.

An animal bite or scratch abroad, from a dog, monkey, bat, or any mammal, means washing the wound with soap and water and getting medical care the same day, even if you had pre-exposure rabies shots. Vaccination after an exposure works, and it has to start promptly; the pre-exposure series simplifies that treatment without replacing it.

The flight and altitude emergencies above hold anywhere: a swollen, painful calf or sudden breathlessness after a long flight, and worsening confusion or breathlessness at elevation, go to emergency care wherever you are.

Separately, yellow fever proof runs on a fixed clock: if your destination requires it and departure is within 2-3 weeks, the certified-clinic appointment belongs on this week's calendar, because the certificate starts counting 10 days after the shot.

Key Takeaways

The pre-travel visit belongs 4-6 weeks before departure, and a visit

within days of leaving still has options; the CDC's phrase is that it is never too late. - Vaccines are destination-driven: the CDC destination pages carry the list, and yellow fever happens only at a certified clinic, with a certificate that becomes valid 10 days after the shot. - Malaria prevention is chosen by region and person from atovaquone-proguanil, doxycycline, mefloquine, and tafenoquine, with the decision made in the visit and the prescription sent to your pharmacy. - The traveler's diarrhea plan is oral rehydration salts, loperamide, and an antibiotic reserved for severe illness, often azithromycin for South and Southeast Asia. - The kit rules: original labeled bottles in the carry-on, whole-trip supply plus a buffer, EPA-registered repellent plus permethrin for clothing, and an insurance check that covers care abroad and evacuation.

Travel Medicine in Philadelphia - the service page: how the consultation works and when Penn Travel Medicine gets involved
The adult vaccine schedule - the routine shots every itinerary rides on
Travel medicine at the practice - the service page for pre-trip consults
Cyclospora - the parasite behind post-trip diarrhea that keeps relapsing
Hydration and electrolytes - the rehydration half of the diarrhea plan
Same-day sick visits - for the illness that comes home with you

Scientific References

Centers for Disease Control and Prevention. "Before You Travel." CDC Travelers' Health. CDC
Centers for Disease Control and Prevention. "Destinations." CDC Travelers' Health. CDC
Centers for Disease Control and Prevention. "Last-Minute Travelers." CDC Yellow Book. CDC
Centers for Disease Control and Prevention. "Travelers' Diarrhea." CDC Yellow Book. CDC
Centers for Disease Control and Prevention. "Food and Water Precautions for Travelers." CDC Yellow Book. CDC
Centers for Disease Control and Prevention. "Hepatitis A." CDC Yellow Book. CDC
Centers for Disease Control and Prevention. "Yellow Fever." CDC Yellow Book, and "Find a Clinic." CDC / Registry
Centers for Disease Control and Prevention. "Malaria," and "Yellow Fever Vaccine and Malaria Prevention Information, by Country." CDC Yellow Book. CDC / Country table
Centers for Disease Control and Prevention. "High-Altitude Travel and Altitude Illness." CDC Yellow Book. CDC
Centers for Disease Control and Prevention. "Understanding Your Risk for Blood Clots with Travel." CDC
Centers for Disease Control and Prevention. "Travel Health Kits." CDC Yellow Book. CDC
Centers for Disease Control and Prevention. "Avoid Bug Bites." CDC Travelers' Health. CDC
US Department of State. "Insurance Coverage Overseas." State.gov
Clarke MJ, Broderick C, Hopewell S, Juszczak E, Eisinga A. "Compression stockings for preventing deep vein thrombosis in airline passengers." Cochrane Database of Systematic Reviews. 2021. Cochrane

Fishtown Medicine | Treatments

2418 E York St, Philadelphia, PA 19125(267) 360-7927 hello@fishtownmedicine.comHSA/FSA Eligible

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Frequently Asked Questions

Common Questions

It depends on the country. The CDC destination pages list recommended and required vaccines for every destination: typhoid and hepatitis A cover the food-and-water risks across much of Asia, Africa, and Latin America, and some countries require yellow fever vaccination for entry. Fishtown Medicine reviews your destination's page with you in the visit and turns it into a schedule with locations and dates.

Only if your itinerary enters a malaria region, and the CDC's country-by-country malaria table answers that destination by destination. Much of sub-Saharan Africa calls for prophylaxis on nearly every itinerary, while many popular destinations need none. Where pills are recommended, Fishtown Medicine chooses among atovaquone-proguanil, doxycycline, mefloquine, and tafenoquine based on the region's resistance patterns and your health, and sends the prescription to your pharmacy.

3 things: oral rehydration salts, loperamide, and, for many destinations, a prescribed antibiotic reserved for severe illness. Azithromycin is the usual antibiotic choice for South and Southeast Asia because resistance to quinolone antibiotics is common there. Fishtown Medicine sets the when-to-use rules with you before departure, so a bad night abroad comes with instructions instead of guesswork.

Coverage varies by plan and by vaccine. Hepatitis A is part of the routine adult schedule and is often covered, while destination-specific vaccines like typhoid, yellow fever, and Japanese encephalitis are often paid out of pocket at the clinic or pharmacy that gives them. The Fishtown Medicine visit maps out where each shot is available, so you can check your plan against specifics before you commit.

Deep-Dive Questions

Because that is roughly how long the vaccine takes to build protective immunity, and the International Health Regulations set the certificate's start date to match. Countries that require proof of yellow fever vaccination accept the International Certificate of Vaccination or Prophylaxis beginning 10 days after the primary dose, which is why the certified-clinic appointment has to happen at least 10 days before you cross the border that asks for it.

The injectable vaccine is a single inactivated shot, given ideally 2 or more weeks before travel, with protection lasting about 2 years. The oral vaccine is live-attenuated, taken as 4 capsules over a week and finished at least 1 week before departure, with protection lasting about 5 years, which suits frequent travelers. Because the oral form is a live vaccine, it is avoided in pregnancy and with weakened immune systems; between the 2, timing and preference usually decide.

Because Campylobacter, one of that region's most common bacterial causes, is now widely resistant to fluoroquinolone antibiotics there, so azithromycin retains activity where ciprofloxacin often fails. Fluoroquinolones also carry FDA boxed warnings covering tendon, nerve, and other effects, which has made them a less attractive default in general. The CDC Yellow Book names azithromycin the preferred first-line choice for those regions.

Resistance patterns come first: chloroquine-resistant falciparum malaria is the rule nearly everywhere malaria circulates, with the Caribbean and parts of Central America among the few exceptions, so most itineraries choose among atovaquone-proguanil, doxycycline, mefloquine, and tafenoquine. From there the match is personal. Mefloquine is avoided with certain psychiatric and seizure histories, doxycycline adds sun sensitivity, and tafenoquine requires a G6PD enzyme test before the first dose. Trip length, budget, and whether a daily or weekly schedule fits your habits settle the rest.

Because the parasite spends its first days maturing in the liver before it enters the blood. Drugs that act only on blood stages, doxycycline and mefloquine among them, have to continue for 4 weeks after you leave the region to cover parasites still emerging from the liver, while atovaquone-proguanil also kills liver stages and stops 7 days after departure. Stopping early is one of the classic ways prophylaxis fails, so the tail of the course counts as much as the trip itself.

Travelers whose itineraries would make treatment after a bite hard to reach: remote regions far from reliable medical care, long stays in countries where dog rabies circulates, planned work with animals, and caving. Pre-exposure vaccination does not remove the need for urgent care after a bite or scratch; it simplifies the treatment, removing the immune globulin injection and reducing the number of doses, and buys time when the nearest clinic is days away.

When the ascent profile reaches the moderate- or high-risk categories in the CDC framework, which include flying directly to sleeping altitudes above about 9,000 feet and itineraries with fast sleeping-altitude gains; Cusco at about 11,000 feet and La Paz above 11,900 feet are the classic fly-in examples. Taken starting before ascent, acetazolamide speeds acclimatization and prevents acute mountain sickness. Gradual ascent and sleeping lower than the day's high point do as much work as the medicine, so route design comes first and the drug supports it.

Imperfectly. Studies of travelers who follow the classic rules still find substantial rates of illness, in part because restaurant hygiene is outside the traveler's control, and CDC guidance acknowledges that counseling on food and water choices alone has limited measured effect. The precautions still tilt the odds and also reduce exposure to typhoid and hepatitis A, so the evidence-based answer is both: follow them where you can, and carry a self-treatment plan for when they are not enough.

In 3 ways. Live vaccines, including yellow fever and oral typhoid, are generally contraindicated, so a yellow-fever-requiring destination may involve a formal medical waiver letter from a certified clinic instead of the vaccine. Infections that are self-limited for most travelers carry higher stakes, which moves the threshold for prophylaxis and for seeking care abroad. And the timeline stretches: immunocompromised travelers benefit from the earliest possible pre-travel visit and a written plan for where to get care at the destination.

A Cochrane review of randomized trials in airline passengers found that graduated compression stockings produced a large reduction in symptomless deep vein thrombosis on flights of several hours or more. For travelers with risk factors, recent surgery, prior clots, pregnancy, estrogen use, active cancer, properly fitted below-knee stockings are a cheap, evidence-backed step, and for travelers without risk factors, movement, hydration, and in-seat calf exercises capture most of the achievable benefit.

Not always. Some medicines that are routine in the United States, including certain stimulants, sedatives, and even some over-the-counter cold ingredients, are restricted or banned in other countries, so travelers carrying controlled or unusual medications should check with the destination country's embassy before flying. Everything should travel in its original labeled container, in the carry-on, with prescription copies that name the generic drug; those copies answer most questions a border officer has.

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