Methoprene is an antiparasitic active ingredient used in veterinary medicine in dogs, cats and livestock against a few external parasites (lice, flies, etc.). It is also used against agricultural and household pests. It is a so-called Insect Growth Regulator (IGR) belonging to the chemical class of the juvenile-hormone analogues.

Common name: METHOPRENE

Other names: (S)-methoprene
Chemical class: juvenile hormone analogue, insect development inhibitor


Molecular structure of METHOPRENE





Type of action: contact and oral larvicide
Main veterinary parasites controlled: larvae (maggots) of insects: flies, mosquitoes, fleas, etc.

Efficacy against a specific parasite depends on the delivery form and on the dose administered. National regulatory authorities determine whether a product is approved for a given indication, i.e. use on a particular host at a specific dose and against a specific parasite. Check the labels of the products available in your country.

Click here for general information on features and characteristics of PARASITICIDES.


(S)-methoprene is an insect growth regulator without systemic effect.

It is used abundantly in flea products (spot-ons, shampoos, sprays, etc), mostly combined with a flea adulticide (e.g. fipronil, imidacloprid, etc). It has no effect against ticks, mites, or any internal parasites. It doesn't kill the fleas, but interrupts their development. The idea is that if some fleas survive the adulticide, methoprene should make them uncapable of producing offspring. Since it is unstable when exposed to sunlight, its residual effect is rather short.

Methoprene is also used as a feed-though insecticide in cattle and horses mainly against horn flies (Haematobis irritans) that develop in the manure.

It is also used aganist agricultural and household pests.

The table below indicates some usual dosing recommendations for (S)-methoprene issued by manufacturers or documented in the scientific literature. They may not be approved in some countries.

Dosing recommendations for METHOPRENE
Delivery Parasites Dose (against methoprene-susceptible parasites)
Spot-on Fleas 6-40 mg/kg, depending on animal's weight
Spot (10%-on) Fleas 5-20 mg/kg, depending on animal's weight
Feed-through Horn flies 75 mg/100 kg bw/month = 34 mg/100 lbs bw/month

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Dosing recommendations for antiparasitics depend on national regulations. National regulatory authorities determine whether a product is approved for a given indication, i.e. use on a particular host at a specific dose and against a specific parasiteCheck the labels of the products available in your country for specific information on approved indications.


Oral LD50, rat, acute*: >34600 mg/kg
Dermal LD50, rat, acute*: >3500 mg/kg
* These values refer to the active ingredient. Toxicity has to be determined for each formulation as well. Formulations are usually significantly less toxic than the active ingredients.

MRL (maximum residue limit) set for animal tissues (either beef, mutton pork or chicken)*:

  • CODEX: Yes
  • EU: Yes (Annex IIIA)
  • USA: Yes
  • AUS: Yes

* This information is an indicator of the acceptance of an active ingredient by the most influential regulatory bodies for use on livestock. MRL's for animal tissues may be set also for agricultural pesticides that are not approved for use on animals but are used on commodities fed to animals. A MRL may be also set in the form of an IMPORT TOLERANCE for active ingredients not approved in a particular country but approved for imported animal commodities.

Withholding periods for meat, milk, eggs, etc. depend on delivery form, dose and national regulations. Check the product label in your country.

Learn more about methoprene safety.

General safety information for antiparasitics is available in specific articles in this site (click to visit):


Never use agricultural or hygiene products with this or any other active ingredient on livestock or pets, even if there are veterinary products with this same active ingredient approved for use on animals. The formulations for agricultural or hygiene use are different and may be toxic for livestock or pets.

It is obvious that veterinary products are not intended for and should never be used on humans!!!


Decade of introduction: 1970
Introduced by: ZOECON
Some original brands: ALTOSID, PRECOR
Patent: Expired (particular formulations may be still patent-protected)

Use in LIVESTOCK: Yes, scarce
Use in HORSES: YES, very scarce
Use in
DOGS and CATS: Yes, moderate
Main delivery forms

Use in human medicine: No
Use in
public/domestic hygiene: Yes
Use in
agriculture: Yes
Generics available: 


In livestock: Yes, in houseflies (Musca domestica) and in mosquitoes.
In pets: No


Methoprene is a Juvenile Hormone Analogue acting as an insect development inhibitor effective against numerous insect species, but with no effect whatsoever on ticks or mites. It only interferes with the molt from pupae to adults, i.e. it does not kill insect larvae and consequently it cannot be used against various myiases.

In livestock it is only used in a few feed additives for cattle against horn flies sometimes used also in horses. Fed to cattle a large portion goes unchanged through the gut (feed-though), is excreted with the feces and acts upon the larvae of flies developing in the manure.

In dogs and cats it is mostly used in combination with flea adulticides in numerous spot-ons (= squeeze-on = pipettes), as well as in shampoos, soaps, sprays, etc. It is used to extend the efficacy of flea control products to the development stages of the fleas, since most flea adulticides have an insufficient impact on the developmental stages in the pets' environment.

Pharmacokinetics of methoprene

Topically administered methoprene is poorly absorbed through the skin. After oral administration to cattle most of the administered dose is excreted unchanged through the feces. The rest is absorbed, metabolized and excreted through urine, feces and expired breath. About 20% of the administered dose is excreted through urine in the form of various metabolites.

Mechanism of action of methoprene

Methoprene and other Juvenile Hormone Analogs suppress or stimulate the expression of various genes involved in insect metamorphosis otherwise regulated by natural juvenile hormone. Depending on which gene is affected different biochemical and cellular effects will result. The bottom line is that development is disturbed and interrupted.

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