Mebendazole — on the WHO Essential Medicines List since 1977 — treats pinworm, roundworm, hookworm, and whipworm infections. This 2026 guide covers the beta-tubulin blocking mechanism, dosage by indication, why pinworm needs only 1 dose vs 3 days for others, side effects, mebendazole vs albendazole comparison, and critical pinworm reinfection prevention steps.