Carvacrol is a natural active ingredient of plant origin used in veterinary medicine mainly in dogs and cats against some external parasites (lice, fleas, flies, etc). It is also used against agricultural and household pests.

Common name: CARVACROL

Other names: 5-Isopropyl-2-methylphenol, cymophenol

Some plants where it is found

  • Monarda fistulosa (wild bergamot, bee balm)
  • Nepeta cataria (catnip, catswort, catmint)
  • Origanum vulgare (wild marjoram), Origanum majorana (sweet marjoram), Origanum dictamnus (Cretan dittany, hop marjoram)
  • Satureja montana (winter savory); Satureja hortensis) (summer savory)
  • Sideritis syriaca (ironwort, mountain tea)
  • Thymus vulgaris (Thyme)
  • etc.


Chemical structure of CARVACROL. Picture taken from


Type of action: insecticide, repellent
Main veterinary parasites controlled: flies, ticks, mites, lice, fleas, mosquitoes, etc., mostly only in experimental studies

Mechanism of action: Little is known about the mechanism of action of carvacrol in insects. Certain studies on Musca domestica suggest that it can bind to the house fly nicotinic acetylcholine receptor, and binding inhibited nicotine binding non-competitively. Studies in cockroaches (Periplaneta americana) showed that carvacrol is an allosteric modulator at insect GABA receptors and binds to the octopamine receptor with high sensitivity.

However, a "crushing" efficacy should not be expected from natural products, comparable to that of modern synthetic insecticides, which are more potent and persistent than any natural compound. Simplifying, it can be said that natural active ingredients can be useful in places or seasons with low parasite challenge, but may be insufficient for controlling well established parasite populations (fleas, ticks, mites, etc.) in pets, let alone in livestock.

Efficacy against a specific parasite depends on the delivery form and on the dose administered. Check the labels of the products available in your country.

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


Oral LD50, rat, acute*: 810 mg/kg
Dermal LD50, rat, acute*: >2700 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.

Carvacrol is a moderate skin irritant and can cause allergies. Being used as a preservative and flavoring agent in products for human consumption it can be considered as rather safe for use on humans and domestic animals.

It must be remembered that the natural origin does not guarantee that such compounds are less toxic than the synthetic parasiticides. They are as "chemical" as the synthetic ones. Toxicity is a matter of dose!

General information on the safety of veterinary antiparasitics is available in specific articles in this site (click to visit):


Carvacrol is the major component in the essential oils of several plants (e.g. in Sideritis syriaca 60-80%; in Origanum majorana 50%, in Satureja spp ≤45%, etc). More or less pure carvacrol is extracted industrially from such oils. But there are also processes for industrial synthesis.

Use in LIVESTOCK: Not directly, only in some essential oils
Use in HORSES: Not directly, only in some essential oils
Use in
DOGS & CATS: Not directly, only in some essential oils

Use in human medicine: Yes, as additive in the food industry, e.g. for preventing microbial contamination
Use in
public/domestic hygiene: ?
Use in
agriculture: Yes, very scarce


Reported in livestock & horses: NO
Reported in pets: NO
Reported in other uses: NO

Learn more about parasite resistance and how it develops.


Mountain tea (Sideritis syriaca). Picture taken from

Carvacrol is an aliphatic terpene naturally produced by numerous plants. It is one of the major components in the essential oils of thyme, marjoram and savory.

Carvacrol is an optic isomer from thymol, i.e. it has the same chemical formula but with a different spatial structure. Many plants that contain thymol contain also carvacrol.

Carvacrol has antimicrobial and gungicidal properties, which explain its abundant use as a natural preservative in food and personal care products (e.g. toothpaste, mouth rinses, etc).

To our knowledge it is not used directly in commercial veterinary antiparasitics. It is used in bees against Varroa mites. Experimental studies have shown efficacy against certain poultry mites (Dermanyssus gallinae).

Carvacrol shares two features with many other natural insecticides: it is rather volatile and is unstable when exposed to sunlight. Consequently its effect in animals exposed to sunlight is very short: a few days or even only a few hours. This means that protection of the treated animals against re-infestations (residual effect) is virtually inexistent. This is particularly unfavorable for livestock that would need to be treated very frequently. However, for the same reason they do not leave chemical residues in food commodities (meat, milk, eggs, etc.), which is a benefit sought by organic producers.

Another disadvantage of many "natural products" extracted from plants is that quality (and thus efficacy) may vary, even if used following the label instructions, because producing extracts from heterogeneous plant materials is often less reliable than chemical synthesis.

Finally it must be said that in many countries registration of so-called "natural products" does not need a (serious) proof of efficacy, quality and safety as pesticides or veterinary medicines. This means that many such products have not been seriously tested in clinical trials in the field and consequently their efficacy and/or safety may not be granted. For such products, getting a market authorization does not need a substantial investment, which explains why there are so many brands in most countries.

  • Click here to view the list of all technical summaries of natural antiparasitic active ingredients in this site.
  • Click here to view the list of all technical summaries of antiparasitic active ingredients in this site.
  • Click here to visit the article on medicinal plants with antiparasitic properties in this site.