Niclosamide 500mg (Niclosamide)

Niclosamide 500mg is an antiparasitic tablet first developed in the 1950s as a teniacide for tapeworm infections. The drug was on the WHO Model List of Essential Medicines for decades as the standard treatment for Taenia saginata, Taenia solium, and Hymenolepis nana infections. Niclosamide remains one of the most selective anti-tapeworm agents ever developed, with a mechanism that targets the parasite mitochondrial oxidative phosphorylation while sparing the host because almost none of the drug is absorbed systemically from the gut (PMID 24735482).

The pharmacology is unusual. Oral niclosamide stays largely in the intestinal lumen, which is exactly where tapeworm scolices attach. This local action gives the drug a strong activity profile against luminal cestodes while producing remarkably few systemic side effects.

Standard antiparasitic use

The classic adult regimen for Taenia infections is a single 2 g oral dose (four 500mg tablets) chewed thoroughly and swallowed with water on an empty stomach. Diagnosis and full workup for intestinal parasites are covered in our intestinal worm treatment guide. For Hymenolepis nana, the regimen is 2 g on day one followed by 1 g daily for six more days, because H. nana has an internal autoinfection cycle that requires a longer course. Cure rates above 90 percent are typical when the regimen is followed correctly.

Albendazole (Zentel) and praziquantel (Biltree) have largely displaced niclosamide in many parts of the world because they cover a wider parasite spectrum. For side-by-side comparisons see mebendazole vs albendazole and fenbendazole vs mebendazole. Niclosamide remains useful where availability of the alternatives is limited, where the diagnosis is specifically intestinal tapeworm, and where the patient cannot tolerate the systemic exposure of an absorbed drug.

Emerging research interest

Beyond its antiparasitic role, niclosamide has attracted significant research interest in oncology, antiviral, and antimicrobial repurposing studies. The molecule inhibits multiple oncogenic signaling pathways (Wnt/beta-catenin, STAT3, mTOR) in preclinical cancer models (PMID 25180068). It also showed in vitro activity against SARS-CoV-2 during the COVID-19 era and has been studied for methicillin-resistant Staphylococcus aureus and Mycobacterium tuberculosis. None of these uses are clinically established. The oral absorption that makes niclosamide so safe as an antiparasitic also limits its utility for any systemic indication, and reformulation work is ongoing.

If you are reading about niclosamide because of a non-parasitic use case, understand that this is research-stage territory. Established clinical use is intestinal tapeworm infection.

Side effects

Because oral niclosamide is essentially unabsorbed, side effects are mostly local: nausea (5 to 10 percent), abdominal discomfort (5 to 10 percent), and loose stools. Drowsiness, rash, and pruritus occur in less than 2 percent. Systemic toxicity is rare.

Contraindications

Avoid in known hypersensitivity. Caution in significant hepatic impairment despite the low systemic absorption. Not recommended in the first trimester of pregnancy as a precaution, though no teratogenicity has been demonstrated.

How to take

Chew tablets thoroughly before swallowing or crush and mix with water. Take in the morning after a light breakfast. A laxative is not required afterward. For T. solium specifically, some clinicians give a laxative two hours later to expel the parasite intact and reduce the theoretical risk of cysticercosis from released eggs, but evidence for this is limited.

For broader antiparasitic options, see Wormiza 444mg (fenbendazole), Wormentel 888mg (fenbendazole higher dose), Biltree 600mg (praziquantel), Ivercor 12mg (ivermectin), Mebex 100mg (mebendazole), or Zentel 400mg (albendazole). See also ivermectin vs mebendazole comparison for choosing between molecule classes.

References

1. Andrews P et al. Acta Trop 1982. PMID 6126081.
2. Chen W et al. Cancer Lett 2018. PMID 24735482.
3. Li Y et al. Curr Top Med Chem 2014. PMID 25180068.

Related Guides

• Niclosamide: The Antiparasitic That Does More Than Kill Tapeworms
• Buy Niclosamide in the USA: Order Online with Fast Delivery
• Intestinal Worm Treatment: Complete Guide
• Mebendazole vs Albendazole for Worms
• Fenbendazole vs Mebendazole Comparison
• Ivermectin vs Mebendazole Comparison