Mebendazole: what it treats, how to take it, side effects
Last updated September 3, 2026.
Mebendazole (brand names Emverm, Vermox) is a chewable deworming tablet used worldwide for intestinal worm infections. It kills pinworm, roundworm, whipworm, and hookworm by cutting off their energy supply, and for pinworm it often works in a single dose.
What does it treat?
Emverm treats pinworm, whipworm, roundworm, and hookworm infections; the older Vermox label covers roundworm and whipworm. Pinworm is by far the most common reason in the US: the intense night-time anal itching, often in school-age kids, that spreads through households and classrooms.
How do you take it?
The tablet is chewed thoroughly before swallowing, with or without food. The dose depends on the worm: pinworm is a single 100 mg tablet once; whipworm, roundworm, and hookworm take 100 mg morning and evening for 3 consecutive days. For pinworm, a second single dose 2 weeks later catches newly hatched worms, and treating the whole household at once is standard because reinfection is the rule otherwise. Missed dose: take it when remembered unless the next dose is near; never double up.
Side effects to know
- Common: abdominal pain, diarrhea, gas, nausea, vomiting, appetite loss, and rash, mostly mild and brief.
- Serious: rare severe skin reactions and, at high or prolonged doses, liver enzyme elevations and low blood counts; standard short courses rarely produce any of these.
Who should not take it?
People with known hypersensitivity to it. Pregnancy is a talk-to-your-doctor situation, especially the first trimester; for pinworm in pregnancy, hygiene measures or pyrantel are often weighed first. Liver disease and significant gut inflammation call for caution, since absorption rises when the gut is inflamed. Children under 1 were not studied, and under-2 use belongs to the doctor. Metronidazole combined with mebendazole has been linked to severe skin reactions and should be avoided.
When is it an emergency?
Call 911 for a spreading blistering rash or facial swelling with trouble breathing after a dose. Severe abdominal pain with vomiting, or signs of liver trouble like yellowing eyes and dark urine, need same-day care. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why did the pinworm come back after treatment?
Almost always reinfection, not drug failure. The tablet kills worms but not their eggs, which survive on bedding, clothing, and under fingernails and re-infect through hand-to-mouth. The standard fix: treat every household member the same day, repeat one dose at 2 weeks, hot-wash bedding and sleepwear, and keep nails short.
Do I chew mebendazole or swallow it?
Chew it. The tablets are formulated to be chewed thoroughly, which spreads the drug through the gut where the worms live. For small children, the tablet can be crushed and mixed into a little food.
Is mebendazole the same as pyrantel pamoate?
Same job, different drug. Pyrantel is the over-the-counter US option for pinworm and roundworm; mebendazole is prescription and covers a broader worm list, including whipworm and hookworm. For straightforward pinworm, both work; stubborn or mixed infections lean mebendazole.
Can I take mebendazole while pregnant?
Only on medical advice, and generally avoided in the first trimester. Pinworm is uncomfortable but not dangerous to a pregnancy, so hygiene measures or alternatives are usually tried first, with drug treatment deferred or chosen carefully by your clinician.
Does one dose really work for pinworm?
One 100 mg chewable tablet cures most infections on paper, but the 2-week repeat dose is what makes it stick, because eggs hatching after the first dose produce the next generation. Skip the second dose and you are gambling against the worm's life cycle.
What side effects should I actually expect?
Most people feel nothing or mild stomach upset: some abdominal pain, gas, nausea, or loose stools over the day or two of treatment. Rash happens occasionally. Anything severe, blistering, or persistent is a call-your-doctor event, but on standard courses that is rare.