WHO Acute Hazard classification of pesticides: Class II, moderately hazardous.

Mechanism of action of Imidacloprid

As other neonicotinoids, imidacloprid is an agonist of the nicotinic acetylcholine receptors. It takes the place of the normal neurotransmitter acetylcholine in the receptors, which cannot be deactivated by acetylcholinesterase and remains irreversibly blocked. This leads to an over stimulation of the nerve cells, to paralysis and to death of the affected insect.

These receptors are found in the central and peripheral nervous system of mammals, but only in the central nervous systems of insects. Neonicotinoids bind much more strongly to insect receptors than to mammal receptors. This makes them relatively safe for domestic animals and humans.

Acute Toxicity and Tolerance of Imidacloprid

  • LD50 acute, rats, p.o. ~450 mg/kg
  • LD50 acute, mice, p.o. 131 mg/kg
  • LD50 acute, rats, dermal >5000 mg/kg
  • As a general rule, dogs and cats tolerate imidacloprid very well.
  • Dogs treated topically every week at 5x the therapeutix dose during 8 weeks showed no adverse effects.
  • Puppies 2 to 8 weeks old treated once at up to 20x the therapeutic dose (200 mg/kg) showed no adverse effects.
  • Cats treated once topically at 8x and 24x the therapeutic dose showed no adverse effects. A weekly topical administration of 5x the therapeutic dose during 8 weeks caused no adverse effects.
  • Kittens (46 days old) treated once topically at 5x the therapeutic dose showed no adverse effects.

Toxic Symptoms caused by Imidacloprid Poisoning

  • The primary symptoms of intoxication with imidacloprid and other neonicotinoids resemble nicotine intoxications.
  • Most frequent symptoms are:
    • Fatigue
    • Convulsions
    • Lethargy
    • Difficult breathing
    • Unstable gait
    • Tremor (uncoordinated trembling or shaking movements)
    • Cramps (sudden, involuntary contractions of muscles)
  • Symptoms appear a few hours after exposure, but depend strongly on the formulation, the dose and the kind of contact (skin, inhalation, ingestion etc).
  • In chronic toxicity studies in rats, the thyroid gland was the most affected organ. High overdosing also lead to retina atrophy in female rats.
  • As a general rule, young animals are more sensitive to overdosing and react stronger.
  • Besides erroneous dosing, overdosing can occur due to excessive licking after spot-on delivery to dogs and cats (particularly in cats due to intense grooming).
  • A frequent administration error in dogs is partial administration to small dogs of spot-ons approved for large animals.
  • A frequent administration error in cats is partial administration to cats of spot-ons approved only for dogs.

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

  • In cats oral intake due to intense grooming can cause hypersalivation (drooling), vomit, breathlessness.
  • Transient skin reactions and eye irritation have been also reported.
  • Never use spot-ons for dogs in cats; never use spot-ons for large dogs in small dogs. It happens that some users want to save money buying large tablets or spot-ons for treating smaller dogs (or even cats!) twice or more times. The risk of overdosing is considerable, either due to erroneous calculations or to unskilled manipulation. In addition, dog medicines may sometimes contain other ingredients that are toxic to cats.
  • Imidacloprid is not approved for use in livestock in most countries (e.g. US, EU, Australia) but is used in cattle in some countries (e.g. in Latin America) mainly in pour-ons against horn flies and also in sheep against lice in Australia. Most such products have very long withholding periods and are not approved for use on dairy animals. Unfortunately little is known about the target-animal safety of such pour-ons.
  • Imidacloprid is used in various products for off-animal use in livestock and poultry facilities against houseflies. (e.g. baits, paint-ons, etc.)

Antidote and Treatment of Imidacloprid Intoxication

  • There is no antidote for imidacloprid poisoning.
  • Treatment consists in preventing further exposure together with supportive and symptomatic measures.
  • In case of dermal exposure rinse the skin with abundant water and soft detergents.
  • After accidental ingestion stomach lavage as well as administration of active charcoal and laxatives is recommended. Vomiting should not be induced.

Pharmacokinetics of Imidacloprid

  • Imidacloprid is quite lipophilic. When applied topically to animals it quickly dissolves in the lipids of the hair-coat and the body surface. This allows a rather long residual effect against fleas.
  • After topical administration to dogs and cats imidacloprid remains mostly on the animal's surface and is not absorbed. However a certain amount can be ingested through licking and grooming. Ingested imidacloprid is vastly absorbed to blood and quickly metabolized in the liver. Excretion runs mainly through urine (~75%) and feces and is completed in about 48 hours.

Environmental Toxicity of Imidacloprid

  • Imidacloprid is toxic to terrestrial birds but not to other ones (e.g. ducks).
  • Imidacloprid is moderately toxic to fish and highly toxic to aquatic invertebrates. For this reason disposal of imidacloprid residues (e.g. in empty containers) in watercourses must be absolutely avoided.
  • Imidacloprid is also highly toxic to bees. Un 2013 EU  banned the use of imidacloprid and other neonicotinoids as a pesticide in certain crops because it is suspected to be associated with the Bee Colony Collapse Disorder.
  • The half-life of imidacloprid in soil is quite long, 48 to 190 days. Persistence is longer in soils with an organic cover.
  • Imidacloprid is moderately soluble in water and has a moderate affinity for organic materials. There is a certain risk of groundwater contamination in porous soils.
  • Imidacloprid is broken down by sunlight.
  • Half-life in water can be longer than 30 days at a pH between 5 and 9.
  • Imidacloprid does not bioaccumulate.
  • Correct use on dogs and cats is unlikely to result in any significant environmental pollution.

Additional information

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

  • Imidacloprid belongs to the chemical class of the neonicotinoids.
  • Imidacloprid is not used in human medicines.
  • Imidacloprid is used in crop pesticides.
  • Imidacloprid is used in public and 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 imidacloprid.


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.