Checked against the FDA label, NIH resources, and CDC guidance; refreshed October 2026. This page explains possible reactions in general terms. It cannot assess your symptoms, so contact your prescriber or pharmacist with personal concerns.
Here’s the reassuring part first: if you’re taking one to three days of albendazole for an intestinal worm, side effects are usually mild or don’t happen at all. Hundreds of millions of children get single-dose deworming tablets every year. Now the other part: when albendazole is used for weeks to treat cysts in the liver, lungs, or brain, the risks change. Some albendazole side effects then need regular blood tests to catch early. This guide sorts those effects by how often they happen, using the incidence figures in the FDA prescribing information, and explains what each one feels like and what to do about it.
Most of the percentages below come from clinical studies of patients treated for hydatid disease and neurocysticercosis, the two uses the FDA approved. Those patients took the drug for much longer than a typical deworming dose, so the numbers tend to overstate risk for short courses.
Common albendazole side effects
These are the effects most often reported in the FDA-approved Albenza label. Each was reported in roughly 4% or more of patients in at least one of the two study groups.
| Effect (label incidence) | What it feels like | What to do |
|---|---|---|
| Abnormal liver tests (16% in hydatid disease; under 1% in neurocysticercosis) | Usually nothing. It shows up on blood work, not as symptoms. | Keep every lab appointment. Most rises are mild to moderate and return to normal after treatment ends. |
| Headache (11% in neurocysticercosis; 1% in hydatid disease) | Dull or throbbing head pain, often in the first days of treatment | Ask your pharmacist which pain reliever is safe for you. Report severe, worsening, or “worst ever” headaches right away. |
| Nausea (4% to 6%) | Queasiness, especially soon after a dose | Take doses with food if your prescriber has told you to. Small, frequent meals can help. |
| Vomiting (4% to 6%) | Throwing up after doses | Call your prescriber if you can’t keep doses down. Don’t take an extra dose to make up for one you vomited unless told to. |
| Abdominal pain (6% in hydatid disease) | Cramping or aching in the belly | Usually temporary. Severe pain, a swollen belly, or pain with fever needs prompt medical review. |
Headaches are far more common in neurocysticercosis treatment because many of them don’t come from the drug. They come from the brain’s inflammatory response to dying cysts. More on that below.
Less common side effects
In the label’s studies, these effects showed up in about 1% to 2% of patients, or slightly fewer.
| Effect (label incidence) | What it feels like | What to do |
|---|---|---|
| Reversible hair loss (2% in hydatid disease; under 1% in neurocysticercosis) | More hair than usual on your pillow or in the shower drain, sometimes overall thinning | Mention it to your prescriber. Hair typically grows back after treatment ends. |
| Raised pressure inside the skull (2% in neurocysticercosis) | Severe headache, vomiting, blurred vision, drowsiness | Seek urgent care. This is why steroids are often given with treatment for brain cysts. |
| Meningeal signs (1% in neurocysticercosis) | Stiff neck, headache, sensitivity to light | Seek urgent care for assessment. |
| Dizziness and vertigo (about 1%) | Lightheadedness, or a spinning feeling | Sit or lie down until it passes. Don’t drive if you feel unsteady. |
| Fever (1% in hydatid disease) | Raised temperature, chills | Call your prescriber. During long courses, fever can also be a sign of low white blood cells. |
| Allergic-type reactions (reported in clinical references) | Itching, hives, rash | Stop and call your prescriber. Facial or throat swelling or trouble breathing is an emergency. |
The NIH’s StatPearls review of albendazole also lists hives and itching as possible hypersensitivity reactions, and describes the hair loss as telogen effluvium, a temporary shedding phase that usually reverses after the drug is stopped.
Rare but serious side effects
These are uncommon, and most come from post-marketing reports, where exact frequencies can’t be calculated. They are the reason long courses come with lab monitoring.
| Effect | What it feels like | What to do |
|---|---|---|
| Bone marrow suppression: low white cells (leukopenia, granulocytopenia, agranulocytosis), pancytopenia, aplastic anemia | Fever, sore throat, mouth sores, frequent infections; unusual tiredness or pale skin; easy bruising, nosebleeds, or bleeding gums | Call your prescriber the same day. The label reports deaths from granulocytopenia or pancytopenia, and the drug is stopped if counts drop significantly. |
| Hepatitis and acute liver failure | Yellow skin or eyes, dark urine, pale stools, upper-right belly pain, deep fatigue | Seek prompt care. The label advises considering stopping treatment if liver enzymes rise above twice the upper limit of normal. |
| Neurologic reactions in neurocysticercosis: seizures, focal weakness or numbness, sudden severe headache | A seizure, new weakness on one side, slurred speech, confusion | Call 911. These come from inflammation around dying cysts. |
| Retinal damage (when cysts are in the eye) | Blurred vision, new floaters, vision loss | Urgent eye assessment. Doctors check the retina before treating brain cysts for this reason. |
| Severe skin reactions: erythema multiforme, Stevens-Johnson syndrome | Target-shaped spots, blistering, peeling skin, sores in the mouth or eyes, often with fever | Emergency care. Stop the drug and don’t take it again. |
| Rhabdomyolysis | Severe muscle pain or weakness, very dark (cola-colored) urine | Seek urgent care. |
| Acute kidney injury | Much less urine than usual, swelling, confusion | Seek urgent care. |
To put these in context: in the label’s studies, treatment was stopped because of low white cell counts in only 0.7% of patients, and because of liver abnormalities in 3.8% of hydatid disease patients. Serious effects are real, but uncommon.
Your personal risk depends on several things: how long you take the drug, whether your liver is healthy, whether parasites are in an organ like the liver or brain, and which other medicines you take. A healthy child getting a single school-program tablet and an adult with liver cysts on a third 28-day cycle are in very different situations, even though the medicine is the same. If you’re not sure which group you fall into, ask your prescriber how closely you’ll be monitored and which symptoms they want to hear about.
Quick answers: albendazole side effects FAQ
How long do albendazole side effects last?
After a short course, mild stomach upset or a headache usually fades within a day or two. The active metabolite has a half-life of about 8 to 12 hours, so it clears quickly. Hair loss and liver enzyme changes from long courses take longer to return to normal, often weeks after the last dose.
Does albendazole make you tired?
Fatigue isn’t one of the main effects listed on the label. But tiredness with pale skin, or tiredness with fever and sore throat, during a long course can point to low blood counts. Report it.
Can albendazole cause diarrhea?
Some people get loose stools or general stomach upset, and the worm infection itself often causes diarrhea too. Drink plenty of fluids. Call your doctor if you have blood in your stool, signs of dehydration, or diarrhea lasting more than a couple of days.
Will my hair grow back?
Both the FDA label and StatPearls describe albendazole-related hair loss as reversible. Regrowth usually happens over the months after treatment ends.
Is it normal to feel worse before feeling better?
For brain cysts, sometimes, as dying parasites trigger inflammation. That’s expected and why steroids are used, but severe symptoms still need urgent care. For intestinal worms, feeling much worse is unusual and worth a call to your doctor.
Can I stop taking albendazole if I get side effects?
Call your prescriber first, unless you’re having an emergency such as a severe rash or trouble breathing. Stopping a cyst treatment early can leave parasites alive, and your doctor may be able to manage the side effect or adjust the plan.
Short course vs long course: why the risk differs
Albendazole is the same drug in both situations, but the exposure is very different.
| Factor | Short course (intestinal worms) | Long course (hydatid cysts, neurocysticercosis) |
|---|---|---|
| Typical length | One dose to three days; pinworm repeats once after two weeks | 8 to 30 days for neurocysticercosis; up to three 28-day cycles for hydatid disease |
| Food timing | Often an empty stomach, so the drug stays in the gut | With meals, to raise blood levels (a fatty meal can raise them about fivefold) |
| Drug exposure in the body | Low and brief | Higher and sustained |
| Main concerns | Mild stomach upset, headache | Liver enzyme rises, low blood counts, hair loss, inflammation from dying cysts |
| Lab monitoring | Usually none | Blood counts and liver tests on a set schedule |
Two things drive the higher risk of long courses. The first is cumulative exposure: liver and bone marrow effects are more likely when the drug is in the bloodstream for weeks. The second is the parasite: killing a large cyst inside an organ releases parasite material that the body reacts to, and in the brain that reaction can cause symptoms of its own. Our main guide on what albendazole is and how it works covers the dosing schedules in more detail.
Medicines that can raise the risk of side effects
Some drugs change how much active albendazole builds up in your body. More drug can mean more liver and bone marrow effects; less drug can mean the treatment doesn’t work as well. The FDA label and StatPearls describe these interactions:
| Medicine | Effect on albendazole | Why it matters for side effects |
|---|---|---|
| Dexamethasone | Trough levels of the active metabolite about 56% higher | Usually given on purpose in neurocysticercosis, but it adds to total exposure, so lab monitoring still matters |
| Praziquantel | Peak level and overall exposure about 50% higher | Combination therapy for several brain cysts means more drug in the body and closer follow-up |
| Cimetidine | About double the levels in bile and cyst fluid | More drug at the site of hydatid cysts |
| Theophylline | Albendazole may change how theophylline is processed | Theophylline levels should be checked during and after treatment |
| Phenytoin, carbamazepine, phenobarbital, rifampin | Can substantially lower albendazole levels | Fewer side effects, but possibly a weaker effect on the parasite; your doctor may adjust the regimen |
Tell your doctor about any history of low blood counts or recent chemotherapy, too. StatPearls advises closer observation for people with other risk factors for bone marrow suppression.
Managing mild albendazole side effects at home
Most of the common reactions are manageable with simple steps. Check with your pharmacist before adding any over-the-counter medicine, though, especially during a long course when your liver is being monitored.
- Nausea: If your instructions say to take the drug with food, eat a proper meal, not just a cracker. Sip water or ginger tea, and avoid lying flat right after a dose.
- Mild headache: Rest, stay hydrated, and ask your pharmacist which pain reliever suits you. Acetaminophen is processed by the liver, so check before using it during a long course, and stay within label limits.
- Stomach cramps or loose stools: Drink fluids, eat bland foods for a day, and keep a note of how long it lasts.
- Dizziness: Get up slowly, and don’t drive or operate machinery until you know how the medicine affects you.
- Hair shedding: Use a gentle shampoo, avoid harsh treatments, and remember that the label describes it as reversible.
Keeping a simple symptom diary, with the date, the symptom, how bad it was, and when you took your dose, makes your next appointment far more useful. It helps your doctor tell drug side effects apart from the infection or other causes.
Lab tests your doctor may order
The FDA label sets out a monitoring schedule for multi-week treatment:
- Complete blood count (CBC): at the start of each 28-day cycle and every two weeks during treatment, to catch drops in white cells, red cells, or platelets. People with liver disease, including hydatid cysts in the liver, need more frequent counts because their bone marrow risk is higher.
- Liver function tests (LFTs): at the start of each cycle and at least every two weeks. Enzymes above twice the upper limit of normal may lead your doctor to pause or stop treatment.
- Pregnancy test: before starting, for anyone who could become pregnant.
- Eye exam: before treating neurocysticercosis, to look for cysts in the retina.
- Brain imaging (CT or MRI): to plan neurocysticercosis treatment and check the response afterward. The CDC’s clinical guidance notes that calcified (already dead) cysts don’t benefit from anti-parasitic drugs, which is one reason imaging comes first.
A short deworming course usually doesn’t need any of these blood tests unless you have liver disease or other risk factors.
Special groups
Pregnancy
In rats and rabbits, albendazole caused embryo toxicity and skeletal malformations at doses below the human dose. Human data are limited. The FDA label advises against use in pregnancy unless there’s no alternative, and recommends a negative pregnancy test before starting and effective contraception during treatment and for one month afterward. MedlinePlus patient guidance lists a shorter contraception window, so confirm with your prescriber. WHO deworming programs do treat pregnant women after the first trimester in areas where worms are common, because untreated hookworm anemia also harms mother and baby. That decision is made at the population level in high-burden settings.
Breastfeeding
According to the NIH’s LactMed database, only small amounts pass into breast milk. After a single 400 mg dose, modeling estimated the infant would receive about 0.6% of the mother’s dose. A WHO consultation group concluded a single dose can be given to breastfeeding women. Longer courses haven’t been studied as well, so talk with your doctor and your baby’s pediatrician.
Children
Children generally tolerate albendazole well, and it’s used in school deworming programs worldwide. The label says effectiveness in children with neurocysticercosis appears similar to adults. For children under 2, CDC guidance on pinworm suggests weighing risks and benefits before treating. Dosing is based on weight, and tablets may be crushed or chewed.
Liver disease
This is the group at highest risk. The liver converts albendazole into its active form, and impaired liver function can raise drug exposure. In a small group of patients with blocked bile flow, exposure rose about sevenfold. Both liver injury and bone marrow suppression are more likely, so expect more frequent blood tests and a lower threshold for stopping treatment.
Older adults
The label notes there isn’t enough data on people 65 and older to know whether they respond differently. Older adults are more likely to take medicines that interact with albendazole, such as theophylline, certain seizure drugs, or steroids, so a full medication review before starting is a good idea.
Safety tips for taking albendazole
- Follow the food instructions on your label. “With meals” or “on an empty stomach” depends on the infection and changes how much drug reaches your blood.
- Keep every lab appointment during long courses. Low blood counts and liver changes usually cause no symptoms until they’re advanced.
- Use reliable birth control if you could become pregnant, for as long as your prescriber advises.
- Share your full medication list, including dexamethasone, praziquantel, cimetidine, theophylline, and seizure medicines, all of which change albendazole levels or are affected by it.
- Limit alcohol during long courses, since both alcohol and albendazole can stress the liver. Ask your prescriber what’s sensible for you.
- Know the infection warning signs. Fever, sore throat, or mouth sores during treatment mean you should call your doctor the same day.
- Take steroids and seizure medicines exactly as prescribed if you’re being treated for neurocysticercosis. They protect your brain from inflammation as the cysts die.
- Don’t share or reuse tablets. A dose that suited one person’s infection may be wrong or unsafe for someone else.
- Finish the course unless your prescriber tells you to stop.
Side effect or the infection itself?
Not every symptom during treatment comes from the drug. There are three common sources of confusion.
Die-off reactions in tissue infections
Living cysts in the brain often hide from the immune system. Once albendazole starts killing them, the immune system notices and causes swelling around each cyst. That inflammation, not a direct toxic effect of the drug, is behind most headaches, seizures, and raised pressure inside the skull during neurocysticercosis treatment. CDC guidance explains that dexamethasone is often given for exactly this reason. Our article on albendazole for neurocysticercosis covers how the treatment is planned.
Ongoing symptoms of the worm infection
Belly pain, nausea, diarrhea, and itching are classic symptoms of intestinal worms. They can continue for a few days after treatment while dead worms pass and the gut lining recovers. With pinworm, itching can last until the second dose clears any newly hatched worms.
Hidden infections that come to light
The label warns that people treated for hydatid disease may have undiagnosed neurocysticercosis, and treatment can trigger neurologic symptoms. Anyone who has lived where pork tapeworm is common should tell their doctor before starting.
If you can’t tell whether a symptom comes from the drug or the disease, report it anyway. Your prescriber can sort it out, sometimes with a blood test or scan. For tapeworm-specific treatment, see albendazole for tapeworm. If side effects are a concern, our comparison of albendazole vs mebendazole explains when the less-absorbed alternative might fit.
When to seek urgent care
Call 911 or go to the emergency room if you have any of these while taking albendazole:
- A seizure, especially a first seizure
- Sudden severe headache with vomiting, confusion, a stiff neck, or drowsiness
- New weakness, numbness, trouble speaking, or loss of vision
- Swelling of the face, lips, tongue, or throat, or trouble breathing
- A blistering or peeling rash, or sores in the mouth or eyes
Call your prescriber the same day for fever, sore throat, or chills; unusual bruising or bleeding; yellow skin or eyes or dark urine; severe belly pain; severe muscle pain with dark urine; or noticeably less urine than usual. If someone has swallowed too many tablets, especially a child, call Poison Control at 1-800-222-1222.
The bottom line on albendazole safety
For most people taking a one- to three-day course for intestinal worms, albendazole causes little more than brief stomach upset or a headache, if anything. The serious side effects in the label, such as bone marrow suppression, liver injury, and neurologic reactions, belong mostly to long, high-exposure treatment of tissue cysts. That’s why those courses come with a schedule of blood tests, steroids when the brain is involved, and close follow-up. Take the drug as directed, keep your lab appointments, know the handful of warning signs that need a same-day call, and talk to your prescriber before changing anything.
