Intestinal Worms: Which One You Probably Have, the Doses, and Why the Second Dose Two Weeks Later Matters
Most articles on this subject discuss helminths in the abstract. The useful version names them, because the symptoms differ, the drugs differ, and two of them have specific traps that matter more than everything else here.
And one of them accounts for the large majority of cases outside the tropics: pinworm. If you are reading this because of an itchy bottom at night, skip to that section.
🔍 Which worm matches which symptoms
| Worm | What it feels like | The giveaway |
|---|---|---|
|
Pinworm threadworm, Enterobius |
Itching around the anus, worse at night, restless sleep, irritability in children. Sometimes vaginal itching in girls | Thin white threads, about 1 cm, visible around the anus at night or on the surface of stool |
|
Roundworm Ascaris |
Vague abdominal pain, nausea, poor appetite. A cough and wheeze a week or two before, as the larvae pass through the lungs | Passing a large worm — 15 to 35 cm, pale and pencil-thick — in stool or vomit |
| Hookworm | Tiredness, breathlessness, pallor, abdominal pain. An itchy rash at the entry site weeks earlier | Iron-deficiency anaemia with no other explanation, especially after walking barefoot on soil |
|
Whipworm Trichuris |
Chronic diarrhoea with mucus or blood, cramping, poor growth in children | rectal prolapse. The hardest of these to clear |
|
Tapeworm Taenia |
Often nothing at all. Mild abdominal discomfort, increased appetite, weight loss | Flat pale segments, like grains of rice or ribbon, in stool or underwear — sometimes moving |
| Strongyloides | Intermittent abdominal pain and diarrhoea, recurrent itchy weals, a fast-moving linear rash on the trunk or buttocks | Can persist for decades after one exposure, and raised eosinophils with no obvious cause. See the warning below |
Two general clues. A raised eosinophil count on a routine blood test is the commonest reason parasites get looked for in the first place — and it is typically normal in pinworm, so a normal count does not exclude that one. And iron deficiency without a bleeding source in anyone with relevant exposure should prompt a stool examination before months of iron tablets.
🪱 Pinworm, which is the one you most likely have
It spreads by eggs on hands, bedding, towels and door handles, and the eggs survive in a house for two to three weeks. Which produces the pattern families recognise: treated, better for a fortnight, and back again.
The reason is not treatment failure. It is that the tablets kill worms and not eggs, and that other people in the house are usually infected without symptoms.
💡 The protocol that actually works, and all four parts matter.
1. Treat everyone in the household on the same day — adults included, whether or not they have symptoms. Treating one person alone is why it comes back.
2. Repeat the dose for everyone in two weeks, to catch worms that hatched from eggs swallowed around the first dose.
3. On treatment day: hot-wash all bedding, nightwear and towels, wipe down door handles and toilet seats, and vacuum bedrooms. Do not shake bedding out, which scatters eggs into the air.
4. For two weeks: short fingernails, no nail biting, hand washing after the toilet and before food, a shower or bath first thing in the morning to remove eggs laid overnight, and close-fitting underwear at night in children.
Diagnosis is usually made on sight. Where it is uncertain, the test is a strip of clear adhesive tape pressed to the perianal skin first thing in the morning before washing, then examined. Pinworm eggs are not found on ordinary stool microscopy, which is why that test comes back negative and the diagnosis gets missed.
🧪 What each test can and cannot find
- 📋 Stool microscopy — finds roundworm, hookworm, whipworm and tapeworm eggs. Three samples on different days, because shedding is intermittent and a single negative means very little
- 🏷️ Perianal tape test — the only way to confirm pinworm
- 🩸 Blood serology — the test for strongyloides, which stool microscopy misses most of the time
- 🧫 Stool antigen tests — for giardia and cryptosporidium, far more sensitive than looking down a microscope
- 📈 Full blood count — eosinophils as above, plus haemoglobin and ferritin for hookworm
- 🖥️ Imaging — only where obstruction, liver or biliary involvement, or cysts are suspected
💊 The doses
Mebenza Chewable (Mebendazole) and Albenza (Albendazole) work by starving the worm of glucose; Ivermectol (Ivermectin) paralyses it through a different channel, which is why it covers organisms the other two do not.
| Infection | Usual adult treatment | Repeat? |
|---|---|---|
| Pinworm | Mebendazole 100 mg once, or albendazole 400 mg once | Yes — at 2 weeks, whole household |
| Roundworm | Albendazole 400 mg once, or mebendazole 500 mg once | Stool check at 2 to 3 weeks |
| Hookworm | Albendazole 400 mg once; a 3-day course for heavy infection. Plus iron replacement | Stool check, and recheck haemoglobin |
| Whipworm | Albendazole 400 mg daily for 3 days. Single doses frequently fail. Albendazole with ivermectin clears it considerably better | Yes, confirm clearance |
| Strongyloides | Ivermectin 200 micrograms per kg daily for 2 days. Mebendazole and albendazole are not the treatment of choice | Serology and eosinophils followed up for months |
| Tapeworm, intestinal | Praziquantel as a single dose, or albendazole 400 mg daily for 3 days | Stool check at 1 to 3 months |
| Mixed infection | ZBD Plus (Albendazole with Ivermectin) covers both the soil-transmitted worms and strongyloides in one regimen | Per the species involved |
- 🍽️ Albendazole is absorbed much better with a fatty meal, which matters for anything outside the gut lumen. For simple intestinal worms it can be taken with or without food
- 🍬 The chewable form suits children and anyone who cannot swallow tablets, which is most of the pinworm population
- 🤢 Side effects are usually mild — brief abdominal discomfort, nausea, occasionally headache. Heavy infections can cause more discomfort as the worms die
- 🧫 Prolonged or high-dose albendazole, used for tissue infections rather than gut worms, needs blood count and liver monitoring. Single doses do not
🚨 Three exceptions that change everything
⚠️ 1. Strongyloides before steroids or immunosuppression. This infection can persist silently for decades. If the immune system is then suppressed — a course of steroids, chemotherapy, a transplant drug, or certain biologics — it can multiply out of control and cause a hyperinfection syndrome that is frequently fatal.
Anyone who has ever lived in or travelled extensively through a tropical or subtropical region, and who is about to start immunosuppressive treatment, should be screened with strongyloides serology first, or treated empirically with ivermectin. Covered in our guide to strongyloidiasis. This is the single most consequential item on this page.
⚠️ 2. Tapeworm and the brain. Pork tapeworm eggs can form cysts in tissue, including the brain, which is a separate condition from the adult worm in the gut. Treating it with albendazole can provoke seizures as the cysts die, so it is managed by specialists with corticosteroid cover and anticonvulsants, never with a routine deworming dose. New seizures or persistent headaches in someone with a tapeworm history need investigating before any treatment.
⚠️ 3. Heavy roundworm burden. A large mass of worms can obstruct the bowel or the bile duct, and treatment that paralyses them can occasionally precipitate it. Severe abdominal pain with vomiting and no bowel movement, or jaundice, needs assessment rather than another tablet.
🦠 When it is not a worm at all
The same symptoms — bloating, loose stools, cramping, fatigue —> are produced at least as often by single-celled parasites, which **do not respond to the drugs above**.
- 💧 Giardia — greasy, foul-smelling diarrhoea, marked bloating and sulphurous wind, often after travel or swimming in fresh water, and frequently followed by temporary lactose intolerance. Treated with Flagyl (Metronidazole), or Nizonide (Nitazoxanide) 500 mg twice daily for 3 days. More detail in our guide to giardiasis
- 🩸 Amoebiasis — bloody diarrhoea with abdominal pain, and a risk of liver abscess. Needs metronidazole followed by a second drug to clear the cysts from the gut
- 🧫 Cryptosporidium — watery diarrhoea, often from water, and prolonged in anyone immunosuppressed
Which is the practical argument against guessing: a stool test distinguishes these in a few days, and the treatments do not overlap. The range is in the antiparasitic category.
🤰 Pregnancy, breastfeeding and young children
- 🚫 Avoid mebendazole and albendazole in the first trimester. After it, they are used where infection is causing real harm, and the decision belongs with a doctor rather than a pharmacy shelf
- 👶 Ivermectin is generally avoided in pregnancy and in children under about 15 kg
- 🍼 Breastfeeding — single doses of mebendazole are generally regarded as compatible; check rather than assume
- 🧒 Under two years of age, doses are reduced and treatment is advised rather than self-directed. For pinworm in a household with a baby, the hygiene measures matter even more than the tablets
🧼 Stopping it coming back
Reinfection, not treatment failure, is almost always the reason worms return.
- 🧼 Hand washing after the toilet and before eating, properly, with the fingernails included. The single highest-return measure for the faecal-oral worms
- 👗 Short fingernails and no nail biting in children with pinworm
- 👟 Shoes on soil. Hookworm and strongyloides enter through the skin of the feet
- 🥗 Wash raw vegetables and fruit, and peel where the water supply is uncertain
- 🥩 Cook pork, beef and freshwater fish through — tapeworms come from undercooked meat and fish, not from poor hygiene
- 🚰 Safe drinking water when travelling, including ice and the water used to rinse salads
- 🐕 Deworm pets on a vet schedule, and clear up after them
- 🚽 Do not share towels within a household during a pinworm episode
⚠️ A word about routine deworming as a health practice. Taking an anthelmintic every few months as a cleanse, without any diagnosis, is popular and not supported by evidence outside public health programmes in high-prevalence regions. It exposes you to the drug for no benefit, it drives resistance, and — the practical problem — it muddies the picture if you later develop symptoms that genuinely need investigating.
Mass deworming programmes exist because in some populations the prevalence is so high that testing everyone costs more than treating everyone. That reasoning does not transfer to an individual with no symptoms and no exposure.
📞 When to seek help
Urgent:
- Severe abdominal pain with vomiting and no bowel movement — possible obstruction
- Jaundice, or severe right-sided upper abdominal pain
- New seizures or persistent severe headache in anyone with a tapeworm history
- Bloody diarrhoea with fever
- Breathlessness, confusion or collapse in someone immunosuppressed with a parasitic infection
Promptly:
- About to start steroids, chemotherapy or an immunosuppressant, with any history of living in or travelling through the tropics — ask for strongyloides screening before treatment begins
- Iron-deficiency anaemia without an obvious cause
- Raised eosinophil count on a blood test
- Symptoms persisting after a full treatment course — identify the species rather than repeating the same tablet
- Pinworm returning repeatedly — usually the household or the repeat dose was missed
- Diarrhoea lasting more than two weeks after travel — test rather than treat blindly, since the likely culprits are protozoa
- Pregnancy or a child under two
- Visible worms or segments, which is worth identifying rather than guessing
- Weight loss, night sweats or fever alongside
❓ Frequently asked questions
Why do I need a second dose two weeks later?
Because the tablets kill worms but not eggs. Eggs swallowed around the time of the first dose hatch afterwards, and the repeat catches them. Skipping it is the commonest reason pinworm appears to come straight back.
Does everyone in the house need treating?
For pinworm, yes — everyone on the same day, adults included, whether or not they have symptoms. Most household members are infected without noticing, so treating one person simply passes it back and forth.
What is the mebendazole dose for pinworm?
100 mg as a single dose, repeated after two weeks, for every member of the household. Albendazole 400 mg once, also repeated at two weeks, is the alternative.
My stool test was negative. Can I still have worms?
Yes. Pinworm eggs are not found on stool microscopy at all and need a perianal tape test, strongyloides needs blood serology, and egg shedding by other worms is intermittent, so three samples on different days are needed.
Why does the same tablet not work for every worm?
Whipworm often survives a single dose and needs three days or a combination with ivermectin. Strongyloides needs ivermectin rather than mebendazole or albendazole. Protozoa such as giardia need entirely different drugs.
What is the giveaway for hookworm?
Iron-deficiency anaemia with no bleeding source, especially after walking barefoot on soil. Treatment is albendazole plus iron replacement, and the haemoglobin needs rechecking afterwards.
Should I be tested before starting steroids?
If you have ever lived in or travelled extensively through the tropics, yes — strongyloides serology, because suppressing the immune system can turn a silent decades-old infection into a frequently fatal hyperinfection.
Is it a worm or giardia?
Greasy, foul-smelling diarrhoea with marked bloating after travel or freshwater swimming suggests giardia, which is a single-celled parasite and does not respond to deworming tablets. A stool test distinguishes them in days.
Can I take deworming tablets in pregnancy?
Not in the first trimester. After it, mebendazole and albendazole are used where the infection is causing real harm, as a medical decision. Ivermectin is generally avoided throughout.
Should I deworm myself regularly as a precaution?
No. Routine cleanses without a diagnosis have no evidence behind them outside public health programmes in high-prevalence regions, expose you to the drug for no benefit, and obscure the picture if real symptoms develop later.
📑 Sources and editorial
- World Health Organization guidance on soil-transmitted helminth infections and preventive chemotherapy, and on the limitations of mass treatment outside high-prevalence settings
- Clinical guidance on the diagnosis and treatment of enterobiasis, including household treatment, repeat dosing and the perianal adhesive tape test
- Comparative efficacy reviews of single-dose albendazole and mebendazole by helminth species, including the reduced efficacy against Trichuris trichiura
- Trial evidence for albendazole combined with ivermectin in trichuriasis and in mixed soil-transmitted helminth infection
- Guidance on strongyloidiasis diagnosis by serology and on screening or empirical treatment before immunosuppression, including hyperinfection syndrome
- Guidance on the management of neurocysticercosis, including corticosteroid and anticonvulsant cover during antiparasitic treatment
- Prescribing information for mebendazole, albendazole, ivermectin, nitazoxanide and metronidazole, including pregnancy restrictions and monitoring for prolonged albendazole courses
- Reviews of intestinal protozoal infection, including giardiasis, amoebiasis and cryptosporidiosis, and of stool antigen testing sensitivity
- Reviews of hookworm-associated iron deficiency anaemia and of eosinophilia as a diagnostic clue in parasitic infection
- Related reading: strongyloidiasis, giardiasis
- Related products: Mebenza Chewable (Mebendazole), Albenza (Albendazole), Ivermectol (Ivermectin), ZBD Plus, Nizonide (Nitazoxanide), antiparasitic category
- RXshop Editorial Team — reviewed by Emily Chen, MD, MPH — Internal Medicine Specialist
Medical Disclaimer: The information in this article is for educational and informational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek guidance from a qualified healthcare provider with any questions you may have regarding a medical condition, and before starting, stopping or changing any medication.