Bhutan does not require any specific vaccinations for entry, but most travel health clinics recommend being up to date on hepatitis A, typhoid, tetanus, and routine vaccinations (MMR, polio). If you are entering from a yellow fever zone, you will need proof of vaccination.
Altitude sickness is the most common health concern for visitors. Paro and Thimphu sit at around 2,200-2,300 metres, which is enough to cause headaches and fatigue in some people. If you are trekking to higher altitudes, take acclimatisation seriously -- ascend gradually, stay hydrated, and consider carrying acetazolamide (Diamox) as a preventive. Symptoms of serious altitude sickness include persistent headache, nausea, and confusion. Descend immediately if these develop.
Malaria is a low risk in the southern border districts (Chukha, Sarpang, Samdrup Jongkhar) but not in the highland valleys where most tourists spend their time. If you are crossing into Bhutan overland through Phuntsholing or spending time in the southern lowlands, consult your doctor about prophylaxis.
Water -- Tap water is not safe to drink. Stick to bottled or boiled water. Your tour operator will usually supply bottled water throughout the trip.
Medical facilities -- Hospitals in Thimphu and Paro can handle basic medical issues, and the Bhutanese government provides free healthcare to visitors. However, facilities are limited and there is no advanced trauma care. For anything serious, you would need evacuation to Bangkok or Delhi. Comprehensive travel insurance with medical evacuation cover is essential.
Pharmacies -- Basic medications are available at pharmacies in the main towns, but selection is limited. Bring any prescription medications you need, plus a good first-aid kit with blister treatment, pain relief, anti-diarrheal medication, and rehydration salts.
Sun -- The UV intensity at altitude is fierce, even on cloudy days. Bring strong sunscreen, sunglasses, and a hat.