WHO Acute Hazard classification: U, Unlikely to present acute hazard in normal use

Mechanism of action of Niclosamide

  • The molecular mode of action of salicylanilides including niclosamide, is not completely elucidated. They all are uncouplers of the oxidative phosphorylation in the cell mitochondria, which disturbs the production of ATP, the cellular "fuel". This impairs the parasites motility and probably other processes as well.
  • Niclosamide acts on the tapeworms also through inhibition of glucose absorption.

Acute Toxicity and Tolerance of Niclosamide

  • LD50 acute, mice, p.o. >1500 mg/kg
  • LD50 acute, rats, p.o. 5000 mg/kg
  • LD50 acute, rats, dermal 2000 mg/kg
  • LD50 acute, rabbits, p.o. 5000 mg/kg
  • LD50 acute, cats, p.o. >1000 mg/kg
  • The safety margin after oral administration is 5 to 7. Usual therapeutic doses p.o.: ruminants 50 to 100 mg/kg; dogs and cats: 70 to 157 mg/kg
  • In ruminants doses 40x higher than the recommended dose did not cause adverse drug reactions.
  • In one study, dogs treated at 5x the therapeutic dose slight liver degeneration and exudate in the renal glomeruli was recorded. In another study oral doses of up to 4500 and 6000 mg/kg/day during 4 weeks did not cause toxic symptoms. In another study oral doses of 100 mg/kg/day during one years didn't cause toxic symptoms.
  • In cats, oral doses of up to 900 mg/kg /day during 4 weeks didn't cause toxic symptoms.
  • As a general rule, due to its low toxicity and scarce absorption into blood intoxications with niclosamide are rather infrequent.

Toxic Symptoms caused by Niclosamide Poisoning

  • Most frequent symptoms of niclosamide are atypical:
    • Behavioral disturbances
    • Vomit
    • Convulsions
    • Hypopnea (abnormal slow repiratory rate)

Niclosamide Side Effects, Adverse Drug Reactions (ADRs) and Warnings

  • In dogs and cats transient vomit and diarrhea have been reported.
  • At therapeutic doses niclosamide usually does not cause ADRs, excepting those previously described, but in a mild and transient form. 
  • Niclosamide is sometimes used in combination with benzimidazoles and/or levamisole. Such combinations do not significantly affect the pharmacological behavior of niclosamide.

Antidote and Treatment of Niclosamide Intoxication

  • There is no specific antidote for niclosamide.
  • Treatment consists in supportive and symptomatic measures.

Pharmacokinetics of Niclosamide

  • After oral administration niclosamide is only marginally absorbed into the bloodstream. Absorbed niclosamide is quickly metabolized and excreted. Unabsorbed niclosamide remains vastly unchanged in the digestive tract and is quickly excreted through feces. Neither the parent molecule nor its metabolites are detected in blood or urine.
  • This low absorption allows a high safety margin for use on animals.

Environmental Toxicity of Niclosamide

  • Niclosamide is toxic to fish, aquatic invertebrates, mollusks and amphibians (frogs, salamanders, etc.).
  • Niclosamide is not harmful to most bird species.
  • Niclosamide is biodegraded in water and soil and is susceptible to photolysis.
  • Half-life in water exposed to UV-light: ~150 hours.
  • Half-life in sediments under aerobic conditions: 1 to 4 days.
  • In water it adheres strongly to suspended particles.
  • Niclosamide has a low potential for bioaccumulation.
  • It can be assumed that correctly used in dogs, cats and livestock, niclosamide is unlikely to be detrimental for the environment, including coprophagous insects.

Additional information

Click here for a list and overview of all safety summaries of antiparasitic active ingredients in this site.

  • Niclosamide belongs to the chemical class of the salicylanilides.
  • Niclosamide is used in human medicines.
  • Niclosamide is used in agriculture as a molluscicide.
  • Niclosamide is not used in public or domestic hygiene as a biocide.
  • Click here for General safety of antiparasitics for domestic animals.
  • Click here for General safety of antiparasitics for humans.
  • Click here for General safety of antiparasitics for the environment.
  • Click here for technical and commercial information on niclosamide.


If you intend to use a veterinary drug containing this active ingredient you must carefully read and follow the safety instructions in the product label.  Always ask your veterinary doctor, or pharmacist, or contact the manufacturer. Be aware that the safety instructions for the same veterinary medicine may vary from country to country.

The information in this page must not be confused with the Materials and Safety Datasheets (MSDS) officially issued by manufacturers for active ingredients and many other chemicals. MSDSs target safety during manufacturing, transport, storage and handling of such materials. This safety summary is a complement to the information on product labels and MSDS.

The toxicity of an active ingredient must not be confused with the toxicity of finished products, in this case parasiticidal drugs or pesticides. Finished products contain one or more active ingredients, but also other ingredients that can be relevant from the safety point of view.

All information in this site is made available in good faith and following a reasonable effort to ensure its correctness and actuality. Nevertheless, no this regarding guarantee is given, and any liability on its accuracy, integrity, sufficiency, actuality and opportunity is denied. Liability is also denied for any possible damage or harm to persons, animals or any other goods that could follow the transmission or use of the information, data or recommendations in this site by any site visitor or third parties.