Walk into a Spanish farmacia with a stomach bug and you can buy loperamide and oral rehydration salts over the counter. That covers symptom relief and hydration. But if you need antibiotics for a bacterial infection — the kind of travellers diarrhea treatment Spain pharmacists cannot dispense without a doctor's note — you are stuck. Getting a receta médica (prescription) as a tourist typically means hours in an unfamiliar clinic, in a language you may not speak, while your body is already making you miserable.
What's Actually Happening in Your Gut?
Traveller's diarrhoea is an acute infection of the digestive tract, most often the small intestine. The cause in roughly 80% of cases is bacteria — with enterotoxigenic Escherichia coli (a specific strain of E. coli) being the single most common culprit worldwide, responsible for 30–50% of all episodes.[1] Other bacterial causes include Campylobacter, Salmonella, and Shigella. Viruses (particularly norovirus) account for about 10–15% of cases, and parasites like Giardia make up a smaller fraction.[2]
Here is how the bacterial form works. The bacteria enter your gut through contaminated food or water. Once attached to the intestinal wall, they release toxins — chemicals that force the cells lining your intestine to pump water and electrolytes out of your body and into the gut. Your intestine, which normally absorbs fluid, is now doing the opposite. The result is the watery, urgent diarrhoea you are experiencing.[3]
Your immune system is not familiar with the specific bacterial strains circulating in a new region. Locals develop tolerance over years of exposure. Your gut has never encountered these particular organisms, so it lacks the antibodies to fight them quickly. This is why traveller's diarrhoea hits tourists hardest — it has nothing to do with a "weak stomach" and everything to do with immunological naivety.[1]
In Spain, the risk is lower than in tropical destinations, but it still affects an estimated 10–15% of visitors each year.[2] Heat accelerates bacterial growth in food. Busy tourist restaurants may hold dishes at unsafe temperatures. Tapas culture — small plates sitting on counters — increases exposure if hygiene standards slip. A change in diet, unfamiliar cooking oils, and even stress from travel all compound the problem.
How Do You Know It's Traveller's Diarrhoea?
The clinical definition is three or more unformed stools in 24 hours, combined with at least one additional symptom: abdominal cramps, nausea, vomiting, fever, or an urgent and uncontrollable need to use the bathroom.[1] Most episodes start abruptly — you feel fine at dinner and are ill by morning.
Mild cases involve three to four loose stools per day with moderate cramping but no fever. Moderate cases bring six or more stools per day, significant abdominal pain, and possibly low-grade fever. Severe cases involve frequent watery or bloody diarrhoea, high fever (above 38.5°C), vomiting that prevents you from keeping fluids down, and signs of dehydration: dizziness, dark urine, dry mouth, and rapid heartbeat.[3]
Most cases of traveller's diarrhoea resolve within two to four days without antibiotics. With antibiotic treatment, the average duration drops to under 24 hours.
The distinction between mild and moderate-to-severe matters because it determines whether you need antibiotics or just supportive care. Mild cases respond well to oral rehydration and loperamide alone. Moderate-to-severe cases — especially those with fever, blood in the stool, or six-plus episodes per day — benefit significantly from a short course of antibiotics, which can cut the illness from days to hours.[4]
Which Medications Actually Work?
Treatment for traveller's diarrhoea has two goals: replace the fluid and salt your body is losing, and — in bacterial cases — kill the organism causing the infection. Here are the medications that accomplish each.
Azithromycin (Zithromax)
Azithromycin is the first-line antibiotic recommended by the American College of Gastroenterology for moderate-to-severe traveller's diarrhoea.[4] It works by binding to bacterial ribosomes — the machinery bacteria use to build proteins — and shutting them down. A single 500 mg dose is effective against most bacterial causes, including Campylobacter strains that are often resistant to other antibiotics. Clinical trials show that a single dose reduces illness duration from an average of 60 hours to under 24 hours.[1]
Ciprofloxacin (Ciproxin)
Ciprofloxacin is an alternative antibiotic that targets a different bacterial enzyme — DNA gyrase — preventing bacteria from copying their genetic material. It was historically the go-to treatment for traveller's diarrhoea, but rising resistance among Campylobacter species (especially in Mediterranean countries) has made azithromycin the preferred first choice. Ciprofloxacin remains effective against most E. coli, Salmonella, and Shigella strains and may be prescribed when azithromycin is not suitable.[4]
Loperamide (Imodium)
Loperamide slows down the contractions of your intestine, giving the gut wall more time to absorb water and reducing the frequency and urgency of stools. It does not treat the underlying infection — it manages the symptoms while your body (or an antibiotic) fights the bacteria. Guidelines recommend it for mild-to-moderate, non-bloody, non-febrile diarrhoea. It can also be combined with antibiotics for faster relief in moderate cases.[4]
Oral Rehydration Salts (Sueroral)
Oral rehydration salts (ORS) are the single most effective intervention for preventing dehydration from diarrhoea — the World Health Organization considers them an essential medicine.[5] Each sachet contains a precise ratio of glucose, sodium, potassium, and citrate. The glucose is not just for energy — it activates a sodium-glucose co-transporter in your intestinal wall that pulls water back into your body even while the infection is trying to push it out.
What Can a Spanish Pharmacy Sell You Without a Prescription?
Spanish farmacias can sell you loperamide (Imodium), oral rehydration salts (Sueroral), probiotics, and basic anti-nausea medications without a prescription. Pharmacists in tourist areas often speak enough English to help, but useful phrases include tengo diarrea del viajero (I have traveller's diarrhoea) and necesito sales de rehidratación (I need rehydration salts). What no Spanish pharmacy can sell you without a receta médica is any antibiotic — azithromycin, ciprofloxacin, or otherwise. Spain enforces prescription-only antibiotic sales strictly, in line with EU regulations aimed at combating antibiotic resistance. If your symptoms are moderate to severe and you need an antibiotic, you will need a prescription from a licensed doctor first.