What Happens to Your Body When You Take Dewormers?

October 11, 2025 •

4 min read

An estimated 1.5 billion people, or 24% of the world's population, are infected with soil-transmitted helminths (parasitic worms) worldwide [1.6.1]. So, what happens to your body when you take dewormers to combat these infections?

Quick Summary

Taking deworming medication initiates a process where the drug targets the parasites, leading to their paralysis or starvation. The body then expels the dead or weakened worms, a process that can be accompanied by mild, temporary side effects.

Key Points

Mechanism of Action: Dewormers work by either starving parasites of glucose (like albendazole and mebendazole) or paralyzing their nervous systems (like ivermectin) [1.2.5].
Expulsion Process: After the worms die, the body expels them through the stool over a few days; modern medicines may dissolve them, so they aren't visible [1.2.3, 1.9.3].
Common Side Effects: Mild side effects like stomach pain, nausea, and diarrhea are common and usually temporary, resulting from the body clearing the parasites [1.2.3, 1.4.4].
Doesn't Kill Eggs: Many common dewormers kill adult worms but not their eggs, often necessitating a second dose after two weeks to prevent reinfection [1.2.1].
Global Impact: Parasitic worm infections affect an estimated 1.5 billion people worldwide, and deworming is a key WHO strategy to control disease [1.6.1].
Safety Profile: Dewormers are generally safe for most people but should be avoided by pregnant women in the first trimester and those with certain chronic conditions without a doctor's advice [1.8.1].
Medical Consultation is Key: It is important to consult a healthcare provider for proper diagnosis and to determine the right type of dewormer and dosage [1.5.1].

The Global Need for Deworming

Parasitic worm infections, known as helminthiases, are among the most common infections around the globe, affecting an estimated 1.5 billion people [1.6.1]. These infections are most prevalent in tropical and subtropical regions with poor sanitation and limited access to clean water [1.6.1]. The main species that infect humans are roundworm (Ascaris lumbricoides), whipworm (Trichuris trichiura), and hookworms (Necator americanus and Ancylostoma duodenale) [1.6.1]. While often asymptomatic in light infections, heavier worm burdens can lead to a range of health issues, including abdominal pain, diarrhea, malnutrition, weakness, and impaired growth and physical development, particularly in children [1.6.1, 1.6.3]. The World Health Organization (WHO) recommends periodic deworming for at-risk groups in endemic areas to control morbidity [1.6.1].

How Deworming Medications Work on Your Body

When you take an anthelmintic, or dewormer, it doesn't wage a direct war on your body's cells. Instead, it selectively targets the biological processes of the invading parasites. The two primary mechanisms of action are starvation and paralysis [1.2.5].

Starving the Parasites

Common dewormers like mebendazole (sold under brand names like Vermox and Ovex) and albendazole work by disrupting the worms' ability to absorb sugars, specifically glucose [1.2.1, 1.2.5]. Parasites depend on glucose from their host for survival and energy. By inhibiting the production of microtubules within the parasite's intestinal cells, these medications effectively block their nutrient uptake [1.3.4]. This leads to the worms' gradual energy loss, immobilization, and eventual death over several days [1.2.1, 1.3.4]. Because these drugs are poorly absorbed by the human digestive tract, they remain concentrated in the gut where the worms reside, maximizing their effectiveness with minimal systemic side effects [1.3.4].

Paralyzing the Parasites

Other medications, such as ivermectin and praziquantel, function by interfering with the nerve and muscle functions of the worms [1.2.4, 1.2.5]. Ivermectin, for example, paralyzes the parasites, causing them to lose their grip on the intestinal wall [1.2.4]. Once dislodged, they are unable to remain in the gut and are naturally expelled from the body through the stool [1.2.5]. Pyrantel pamoate, an over-the-counter option for pinworms, works in a similar paralytic fashion [1.2.6, 1.8.4].

What to Expect After Taking a Dewormer

After taking the medication, it begins to work almost immediately, but it can take several days to kill all the worms [1.2.1]. The experience can vary from person to person.

Expulsion of Worms: In the hours to days following treatment, your body will begin to expel the dead parasites. Historically, you might have seen whole worms in your stool [1.9.3]. However, modern medications like albendazole and mebendazole often cause the worms to be dissolved or broken down within the stool, so you may not see them at all [1.9.3].
Mild Side Effects: It is common to experience some mild and temporary side effects. These can include stomach pain, nausea, dizziness, headache, or diarrhea [1.2.3, 1.4.4]. These symptoms are often due to the body's process of expelling the worms and typically resolve on their own within a day or two [1.2.3, 1.4.4].
Second Dose: Since many dewormers, including mebendazole and albendazole, kill the adult worms but not their eggs, a second dose is often recommended two weeks after the first [1.2.1, 1.9.3]. This second round targets the newly hatched worms before they can mature and lay more eggs, breaking the cycle of infection.

Comparison of Common Human Dewormers

Different anthelmintics are effective against different types of worms. A healthcare provider will recommend the best one for a specific infection.


Feature	Mebendazole	Albendazole	Ivermectin
Mechanism	Starves worms by blocking glucose absorption [1.2.1, 1.2.5].	Starves worms by blocking glucose absorption [1.2.5].	Paralyzes worms by interfering with nerve/muscle function [1.2.4].
Common Uses	Threadworm, whipworm, roundworm, hookworm [1.2.1].	Roundworm, hookworm, pinworm, trichinosis, tapeworm infections [1.3.3, 1.8.4].	Strongyloidiasis (threadworm), onchocerciasis (river blindness), Ascaris [1.7.4, 1.8.4].
Administration	Chewable tablet or liquid, often a single dose repeated in 2 weeks [1.2.1].	Tablet, taken with food, dose varies by infection [1.4.6].	Single-dose tablet [1.7.4].
Common Side Effects	Stomach pain, diarrhea, gas, nausea [1.4.2].	Headache, nausea, stomach pain, dizziness, temporary hair loss [1.4.6].	Headache, muscle aches, dizziness, nausea, diarrhea [1.5.4].
Kills Eggs?	No [1.2.1].	No [1.2.3].	Varies by parasite; primarily targets adult and larval forms.

Safety and Contraindications

Modern deworming medications are generally considered safe and effective, with few and minor side effects for most people [1.6.1, 1.8.5]. However, they are not suitable for everyone. Individuals who should avoid or consult a doctor before taking dewormers include:

Pregnant women, especially in the first trimester [1.8.1].
Breastfeeding women [1.8.1].
Children under 1 to 2 years of age (consult a doctor) [1.8.1].
People with chronic diseases like liver or kidney failure [1.2.3].
Individuals with a known allergy to the medication's components [1.8.1].

Severe side effects are rare but can include allergic reactions (rash, hives, swelling), fever, or signs of liver issues (yellowing skin/eyes, dark urine) [1.4.2, 1.5.5]. If severe reactions occur, it is crucial to seek medical attention immediately [1.8.1].

Conclusion: A Targeted and Effective Process

Taking a dewormer prompts a targeted attack on parasitic worms within your body, primarily through starvation or paralysis, without harming your own cells. The body's subsequent expulsion of these parasites is a natural and effective process. While mild side effects can occur, they are generally short-lived. Due to the high global prevalence of worm infections, these medications serve as a vital public health tool, safely reducing morbidity and improving the quality of life for billions of people [1.6.1, 1.8.2]. Always consult a healthcare professional for diagnosis and to ensure you are taking the correct medication and dosage for your specific situation. You can find more information from authoritative sources like the World Health Organization.

Frequently Asked Questions

Deworming medication starts working immediately after you take it, but it may take several days to kill all the worms in your system [1.2.1].

While older medications would cause whole worms to be expelled, modern dewormers like mebendazole and albendazole often dissolve the worms, so you are unlikely to see them in your stool [1.9.3].

The most common side effects are usually mild and temporary, including stomach pain, nausea, headache, dizziness, and diarrhea [1.2.3, 1.4.4].

Many dewormers kill adult worms but are not effective against their eggs. A second dose, typically two weeks later, is often needed to treat the worms that have hatched in the meantime and prevent reinfection [1.2.1, 1.2.3].

It is generally not recommended to take deworming medication during the first trimester of pregnancy. You should always consult with your doctor if you are pregnant, planning to become pregnant, or breastfeeding [1.8.1].

Yes, dewormers like mebendazole and albendazole are considered safe for children aged 2 years and older. For children under 2, it is best to consult a doctor [1.8.1].

No, modern deworming medications do not require fasting or the use of laxatives. They can be taken at any time of day, though taking them after a meal may help minimize potential stomach discomfort [1.2.3].