From a purely chemical point of view almost all active ingredients with parasiticidal activity (either internal or internal parasiticides) discovered so far are synthetic organic molecules, i.e. they do not occur in nature but have been synthesized in the laboratory. Very few such active ingredients occur naturally in plants or other organisms. And even fewer are of mineral (i.e. inorganic) origin.

Most active ingredients can be grouped into chemical classes or families with similar functional groups, i.e. they share a specific molecular structure. E.g. organophosphates are all derivatives of phosphoric acid.

Active ingredients of the same chemical groups have usually the same mechanism of action at the molecular level. What differs considerably for active ingredients of the same chemical class is often the spectrum of activity, the toxicity to both parasites and non-target organisms, the behavior in the environment, etc.

The most relevant chemical classes of parasiticides discovered so far are the following ones, ordered by spectrum of activity and by the decade the first compounds were introduced, regardless of whether they are still marketed today or not:


Active against both external and internal parasites


Active against external parasites (mainly insectsticks and mites)

  • Organochlorines (1940s): broad-spectrum insecticides and acaricides, nowadays prohibited in most countries.
  • Organophosphates (1950s): broad-spectrum insecticides and acaricides. Are being phased out in some countries.
  • Carbamates  (1950s): broad-spectrum insecticides and acaricides. Are being phased out in some countries.
  • Amidines (1960s): mainly acaricides and tickicides.
  • Synthetic Pyrethroids (1970s): broad-spectrum insecticides and acaricides.
  • Benzoylureas (1970s): development inhibitors (= growth regulators).
  • Juvenile Hormone Analogues (1970s): development inhibitors (= growth regulators).
  • Neonicotinoids (1990s): broad-spectrum insecticides and acaricides.
  • Phenylpyrazoles (1990s): broad-spectrum insecticides and acaricides.
  • Spinosyns (1990s): broad-spectrum insecticides and acaricides, partly systemic.
  • Isoxazolines (2010s): broad spectrum, systemic insecticides and acaricides.

A few relevant ectoparasiticides do not belong to these chemical classes, e.g. cyromazine, dicyclanil.

Other chemicals frequently used on livestock and pets against external parasites are not properly ectoparasiticides, nor build an own chemical class, but they share a common funtionality regarding their use against external parasites:

  • Repellents: do not kill the parasites, but keep them away from the treated animals. They are not properly a chemical class, but a functional class.
  • Synergists: enhance the parasiticidal activity of certain active ingredients or help to overcome resistance.

Endoparasiticides = anthelmintics

active against internal parasites mostly parasitic worms (roundworms, tapeworms, flukes)

A few relevant endoparasiticides do not belong to these chemical classes, e.g. clorsulon, monepantel, nitroscanate, nitroxinil, piperazine derivatives.

Other parasiticides

a few parasiticides are of mineral (i.e. non-synthetic) origin, or are directly obtained from plants:

For specific information you can also select a particular chemical class from the corresponding menu.

  • Click here to learn more about general features of parasiticides such as spectrum of activity, mechanism of action, efficacy, residual effect, safety margin, etc.
  • Click here to learn more about general features of ectoparasiticides.
  • Click here to learn more about general features of endoparasiticides.