Albendazole Side Effects: Common, Serious, and When to Call Your Doctor

If you’ve just been handed a single albendazole tablet for roundworm or pinworm, here’s some good news up front: most people who take one dose, or a short course of a few days, notice little or nothing. Albendazole side effects become more of a concern when treatment stretches over weeks, as it does for tapeworm cysts in the brain or liver.

That’s why this guide is organized differently from a typical side-effect list. Instead of lumping every possible reaction together, it maps risk by treatment length, so you can quickly find the part that matches your prescription.

The Short Version

Why Treatment Length Changes Your Risk

Albendazole is used in two very different ways. For worms living in the intestine, a single tablet or a few days of treatment is typical, and much of the drug stays in the gut. For tapeworm larvae living in tissues, prescribers deliberately push blood levels higher, often by having patients take the drug with meals, and continue treatment for weeks.

The FDA prescribing information is built around those longer tissue-infection courses. Its warnings about blood counts and liver function come mainly from patients treated for weeks to months. Meanwhile, the safety record for single doses comes largely from mass deworming programs, where hundreds of millions of tablets are given every year.

There’s another factor too. With tissue infections, some symptoms come from the parasite dying, not from the drug itself. When a cyst in the brain breaks down, the immune system reacts strongly. That reaction can cause headaches or seizures, which is why brain infections are handled with extra precautions.

If you’d like background on why a prescriber might choose albendazole in the first place, see our encyclopedia of albendazole uses and how the drug works.

Part 1: Albendazole Side Effects With Single-Dose and Short-Course Treatment

Single doses, and courses of up to about three days, are the norm for roundworm, hookworm, whipworm, and pinworm, according to CDC treatment tables. Pinworm treatment is typically repeated once after two weeks.

What People Commonly Notice

Short-course side effects tend to be mild and pass within a day or so. The most commonly reported include:

• Abdominal pain or cramping
• Nausea or, less often, vomiting
• Headache
• Dizziness
• Drowsiness or tiredness
• Loose stools or diarrhea

A school-based study in Kenya, published in PLoS ONE, looked at children given albendazole together with praziquantel. About a quarter reported some symptom afterward, most commonly stomach pain, dizziness, nausea, and headache. Most symptoms lasted a day or less, and none were classified as serious. Because two drugs were given together, the study can’t isolate albendazole alone, but it reflects what mass campaigns often see.

Why Heavy Infections Can Feel Worse

In children or adults with many worms, some stomach discomfort may come from the worms dying and passing. That’s one reason symptoms are often reported more in heavily infected communities. Discomfort that fades in a day is common. Severe or worsening belly pain is not, so call your clinician if that happens.

Rare Problems Even After Short Courses

Short courses aren’t risk-free. LiverTox, the NIH database on drug-induced liver injury, notes that liver injury can appear one to two weeks after a short course of one to three days. Case reports also describe jaundice after a single dose. These events are uncommon, but they’re the reason you should call if you notice yellow skin or eyes or dark urine, even after a single tablet.

Allergic reactions can also occur at any treatment length. We cover those in a dedicated section below.

Side Effect or Symptom of the Infection?

Telling a drug reaction apart from the infection itself isn’t always easy. Many worm infections cause the same symptoms people blame on the medicine.

• Stomach upset and loose stools are common with intestinal worms and with Giardia. If they started before your first dose, they’re more likely part of the infection.
• Tiredness and pale skin can reflect anemia from hookworm blood loss. They can also signal low blood counts on long albendazole courses, so they always deserve a mention.
• Headaches and seizures are classic symptoms of neurocysticercosis. Some people notice a flare early in treatment as cysts break down, which is a known reaction rather than a sign the drug is failing.
• Upper-right belly discomfort can come from a liver hydatid cyst or from drug-related liver irritation. Your blood tests help sort out which.

A simple symptom diary helps. Note the date, the time of your dose, what you ate, and what you felt. Bring it to your follow-up visit so your prescriber can see patterns rather than relying on memory. If you’re unsure what your infection typically causes, our overview of conditions albendazole treats describes each one.

Part 2: Weeks-Long Courses for Tissue Infections

Long courses are mainly used for neurocysticercosis (pork tapeworm larvae in the brain), cystic hydatid disease (dog tapeworm cysts in organs), and a few other tissue infections. The FDA label describes neurocysticercosis courses lasting from about one to four weeks, and hydatid disease treated in repeated monthly cycles with two-week breaks.

Common Side Effects in Clinical Trials

The FDA label reports how often side effects occurred in clinical trials for its two approved uses. The pattern differs by condition:

• Hydatid disease patients most often had abnormal liver function tests (about 16%), followed by abdominal pain, nausea, and vomiting.
• Neurocysticercosis patients most often had headache (about 11%), followed by nausea and vomiting (about 6% each).
• Reversible hair loss occurred in about 2% of hydatid disease patients.
• Dizziness, vertigo, and fever were each reported in about 1% of hydatid disease patients.

The label also notes that treatment was stopped most often because of liver test abnormalities, in a little under 4% of hydatid disease patients.

Serious Side Effect 1: Bone Marrow Suppression

This is the most important warning on the label. Bone marrow produces red blood cells, white blood cells, and platelets. Albendazole can rarely suppress that production, leading to low white cell counts (leukopenia or granulocytopenia), low counts of all blood cells (pancytopenia), aplastic anemia, or agranulocytosis. The label states that deaths have been reported.

Warning signs to report promptly, as listed by MedlinePlus:

• Sore throat, fever, chills, or other signs of infection
• Unusual bruising or bleeding
• Unusual weakness or tiredness
• Pale skin
• Shortness of breath

Who’s at higher risk: The label singles out people with liver disease, including those whose hydatid cysts are in the liver. These patients need more frequent blood count checks. CDC’s toxocariasis guidance echoes this, noting that prolonged albendazole has caused pancytopenia in some patients with impaired liver function.

Serious Side Effect 2: Liver Enzyme Elevation and Hepatitis

Mild rises in liver enzymes are common on longer courses. LiverTox reports that transient, symptom-free elevations occur in up to half of patients treated for more than a few weeks, and these usually settle quickly. Stopping the drug is rarely needed.

Clinically apparent hepatitis is rare. Most cases are mild to moderate and improve after the drug is stopped, but LiverTox describes severe cases, including acute liver failure requiring transplant. It rates albendazole as a highly likely cause of clinically apparent liver injury. Onset is usually within a few days to about two months, and sooner with repeat courses.

Symptoms to watch for:

• Yellowing of the skin or the whites of the eyes (jaundice)
• Dark urine or pale stools
• Pain in the upper right abdomen
• Unusual fatigue, loss of appetite, or nausea that won’t settle

The label recommends that prescribers consider stopping albendazole if liver enzymes climb above twice the upper limit of normal. LiverTox adds that people who’ve had albendazole liver injury should generally not take it again, because injury often recurs. Since alcohol also affects the liver, our separate article on whether you can drink alcohol on albendazole explains how to think about combining the two.

Serious Side Effect 3: Seizures and Raised Pressure in the Brain

This warning applies to people treated for neurocysticercosis, and to anyone who has undiagnosed cysts in the brain. As cysts die, inflammation around them can cause:

• New or worsening seizures
• Severe headache
• Nausea and vomiting
• Drowsiness or unusual tiredness
• Changes in behavior or thinking
• Weakness, numbness, or vision changes on one side

In clinical trials, raised intracranial pressure occurred in about 2% of neurocysticercosis patients and signs of meningeal irritation in about 1%. The label advises starting steroids and antiseizure medicines as needed, and considering steroids during the first week of treatment.

The label also warns that people treated for other conditions can have hidden neurocysticercosis. If you’ve lived in or traveled to areas where pork tapeworm is common and develop neurological symptoms during treatment, contact your prescriber urgently.

Serious Side Effect 4: Retinal Damage

If a cyst sits in the retina, killing it can inflame and damage the eye. For that reason, the FDA label recommends an eye examination for retinal lesions before starting neurocysticercosis treatment. If a retinal cyst is found, the specialist weighs whether treating with albendazole is worth the risk to vision.

Blurred vision has also been reported after the drug reached the market. Any new vision change during treatment deserves a prompt call.

Hair Loss

Hair thinning is one of the more distressing albendazole side effects for many people, though it’s not dangerous. The label lists it as reversible and links it mainly to longer courses. Most people find their hair grows back after treatment ends. If hair loss is significant, mention it to your prescriber, as it may also be worth checking blood counts and liver tests.

Other Reported Reactions

The label lists a handful of rare reactions reported after the drug was marketed. These include muscle breakdown (rhabdomyolysis), acute kidney failure, convulsions, drowsiness, and weakness. They’re uncommon, but unexplained muscle pain, dark urine, or a sharp drop in urination should prompt a call.

Albendazole Side Effects at a Glance: Reference Table

Use this table as a quick guide. It doesn’t replace your prescriber’s instructions.

Side effect	How common / when it tends to appear	What to do
Stomach pain, nausea, vomiting	Common; often within hours to a day of a dose	Usually passes. Call if severe, persistent, or you can’t keep fluids down
Headache, dizziness	Common; headache especially in neurocysticercosis	Rest and hydrate. Call if severe, sudden, or with vomiting or confusion
Raised liver enzymes	Common on courses of several weeks; found on blood tests	Keep scheduled lab tests; your prescriber decides whether to pause
Hepatitis (jaundice, dark urine)	Rare; days to about two months in, or one to two weeks after a short course	Call your prescriber the same day
Low blood counts (fever, sore throat, bruising)	Rare; mainly long courses, higher risk with liver disease	Call promptly; you may need an urgent blood count
Seizures or raised brain pressure	Mainly neurocysticercosis, often early in treatment	Call 911 for a seizure; call your specialist for worsening headache
Vision changes	Rare; risk with retinal cysts	Call your prescriber promptly
Hair thinning	Uncommon; longer courses	Mention at your next visit; usually reverses
Rash, hives, swelling	Uncommon; any treatment length	Call your prescriber; call 911 for swelling or breathing trouble

Monitoring Tests and Their Schedule

If you’re on a long course, lab tests aren’t optional extras. They’re the main safety net. Based on the FDA label, monitoring generally includes:

• Complete blood count (CBC): At the start of each 28-day treatment cycle and every two weeks during treatment. People with liver disease may be checked more often.
• Liver function tests: Before each treatment cycle and at least every two weeks during treatment.
• Pregnancy test: Before starting treatment in anyone who could become pregnant.
• Eye exam: Before starting treatment for neurocysticercosis, to look for retinal cysts.

Your prescriber may add imaging (such as MRI, CT, or ultrasound) to check how the cysts are responding. If a lab result is abnormal, they’ll decide whether to continue, pause, or stop. Try to schedule blood draws in advance so a busy week doesn’t push them back.

For single doses for intestinal worms, routine lab tests usually aren’t needed in otherwise healthy people.

Who Has a Higher Risk of Side Effects?

Some people need extra caution or closer monitoring:

• People with liver disease or liver cysts. The label reports that patients with bile flow obstruction had much higher blood levels of the active metabolite, and liver disease raises the risk of bone marrow suppression.
• People with brain cysts. Neurological reactions are tied to the inflammation of dying cysts.
• People who are pregnant or could become pregnant. Animal studies showed harm to the developing fetus. The label calls for effective birth control during treatment and for three days afterward. Our guide on albendazole safety in pregnancy and breastfeeding explains the evidence.
• People with prior reactions to benzimidazoles. The label contraindicates albendazole in anyone with known hypersensitivity to this drug class, which includes mebendazole.
• People taking interacting medicines. Dexamethasone, praziquantel, and cimetidine can raise levels of the active metabolite. See our guide to albendazole interactions with medicines and supplements.
• Older adults. The label notes that there isn’t enough data in people 65 and older to know whether they respond differently.

Allergic Reactions

Allergic reactions to albendazole are uncommon but possible. In clinical trials, rash and hives were reported in under 1% of patients. Rare, severe skin reactions, including erythema multiforme and Stevens-Johnson syndrome, have been reported since the drug reached the market.

Call your prescriber if you develop a new rash or itchy hives.

Call 911 if you notice any of these:

• Swelling of the face, lips, tongue, or throat
• Trouble breathing or swallowing
• Blistering, peeling skin, or sores in the mouth or eyes
• A fast heartbeat with dizziness or fainting

Missed Doses and Side Effects

Doubling up after a missed dose won’t make up the difference faster, and it could increase side effects. MedlinePlus advises against taking a double dose. If you’ve forgotten a tablet, our guide on what to do if you miss an albendazole dose walks through the general rules.

Reporting Side Effects to FDA MedWatch

Tell your prescriber about any side effect that bothers you or doesn’t go away. You can also report it directly to the FDA through MedWatch, either online or by calling 1-800-FDA-1088. Reports from patients and clinicians help the FDA spot rare problems that clinical trials may miss.

When you report, it helps to have the drug name and strength, the manufacturer if it’s on your bottle, your start date, and a description of what happened.

When to Call Your Doctor vs. Go to the Emergency Room

Practical Tips to Lower Your Risk

1. Follow the food instructions. Some courses are taken with meals and others on an empty stomach. Ask if you’re not sure which applies to you.
2. Keep every lab appointment. On long courses, blood tests catch problems before symptoms appear.
3. Share your full medication list, including supplements and over-the-counter products. Steroids, seizure medicines, and acid reducers like cimetidine are especially relevant.
4. Go easy on alcohol, especially on long courses, since both affect the liver. Our guide to mixing albendazole and alcohol explains why.
5. Use reliable birth control if you could become pregnant, during treatment and for three days afterward.
6. Don’t share or self-prescribe. Albendazole taken without a diagnosis can unmask hidden brain cysts and trigger seizures.

Frequently Asked Questions About Albendazole Side Effects

What are the most common albendazole side effects?

Stomach pain, nausea, vomiting, headache, and dizziness are the most common. With longer courses, abnormal liver tests and reversible hair thinning also become more likely.

How long do albendazole side effects last?

After a single dose, mild effects usually fade within a day or so. On longer courses, effects like headache or liver test changes may last while you’re on treatment and typically improve after it ends. Hair regrowth can take longer.

Does albendazole cause hair loss?

It can, mainly during longer courses. The FDA label describes the hair loss as reversible, and it was reported in about 2% of hydatid disease patients in trials.

Can albendazole damage the liver?

Mild liver enzyme rises are common on long courses and usually harmless. Serious hepatitis is rare but can happen, which is why liver tests are checked every two weeks during extended treatment.

Why do I need blood tests while taking albendazole?

Long courses can rarely suppress bone marrow and lower blood counts, and they can affect the liver. Blood tests catch these changes early, often before you’d feel anything.

Is it normal to feel worse when treating neurocysticercosis?

Some worsening of headache can happen as cysts die and cause inflammation. That’s why steroids and seizure medicines are often given. Severe or sudden symptoms still need urgent care.

Is single-dose albendazole safe for kids?

Single doses are widely used in children, and WHO deworming programs report few and minor side effects. CDC notes safety data are more limited under age 6, so your child’s clinician decides.

Can albendazole cause seizures?

In people with brain cysts, the inflammation from dying parasites can trigger seizures. Seizures in people without neurocysticercosis are rare but have been reported. Call 911 for any seizure.

Final Thoughts

For most people taking a single tablet or a few days of treatment, albendazole side effects are mild and short-lived. The picture changes with longer courses for brain or organ cysts, where bone marrow suppression, liver injury, and neurological reactions are real risks that your care team manages through scheduled blood tests, eye exams, and supporting medicines.

Knowing which group you’re in helps you watch for the right warning signs. Keep your appointments, report symptoms early, and never adjust your dose on your own.

Sources

• DailyMed (NIH): Albendazole tablets prescribing information
• MedlinePlus: Albendazole
• LiverTox (NIDDK): Albendazole
• CDC: Clinical Care of Soil-transmitted Helminths
• CDC: Clinical Care of Cysticercosis
• WHO: Soil-transmitted helminth infections fact sheet
• Njenga et al., PLoS ONE (2014): Adverse events after albendazole and praziquantel co-administration
• FDA MedWatch: Safety Information and Adverse Event Reporting

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Medical disclaimer: This CaresKit article is for general educational purposes only and does not replace professional medical advice, diagnosis, or treatment. Always consult your doctor, pharmacist, or another qualified health professional about your own situation before starting, stopping, or changing any medication. In an emergency, call 911. For a suspected overdose or poisoning, contact Poison Control at 1-800-222-1222 or poisonhelp.org.