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There are dozens of products available for treating or preventing flea and tick infestations in
cats and dogs. By the end of this module you will:

  • be able to make sense of the range of products by understanding the active ingredients;
  • know what is required for a product to be a licensed veterinary medicine;
  • know the difference between short- and longer-acting products;
  • know how to report a side effect of a medicine;
  • understand how prescription products differ from non-prescription products.

Fleas and ticks need to feed on blood to survive, which is why they like to land on our pets and bite them. Flea and tick infestations can cause discomfort to the animal, they can lead to allergic skin conditions and they can sometimes transmit diseases to pets, such as the tapeworm Dipylidium caninum (which is transmitted by fleas) and Lyme disease (transmitted by ticks).

Although there are dozens of different brands of non-prescription flea and tick products, if you look more closely, they all contain one or two out of 14 different active substances (drugs). That’s still quite a big number, but when you group the ingredients by the job they do, the range becomes much simpler.

Drugs that kill fleas and ticks (insecticide and acaricide)  





Fipronil is by far the most common ingredient in flea and tick products. 

Drugs that kill fleas (insecticides)

imidacloprid (also kills flea larvae)





Piperonyl butoxide is an ingredient in products that contain pyrethrins. It has no parasiticide activity itself. It is there to extend the duration of the insecticidal effects of pyrethrins.

Drugs that repel and kill ticks (repellent and acaricide). These substances deter ticks from landing on or biting or feeding on the animal, and kill ticks on the animal.



Drugs that halt the life cycle of the flea (known as insect growth regulators or insect development inhibitors). These prevent fleas from laying eggs or stop larvae from developing into adult fleas. They don’t kill adult fleas already on the animal but they can help break the cycle of infestation.




Some products contain an insecticide plus an insect growth regulator (e.g. Frontline Plus and Fiprotec Combo contain fipronil and (S)-methoprene).

Insecticide and acaricide drugs affect the workings of the nervous system of fleas and ticks, which kills them.

Any product that claims to treat or prevent flea or tick infestations in animals must have a marketing licence from the Veterinary Medicines Directorate or the European Medicines Agency, the government organisations that regulate veterinary medicines. To get a licence a company has to show proof of the quality and safety of the product and show evidence that it kills fleas (or ticks or larvae) in tests in which the product has been used as recommended on cats and dogs infested with fleas or ticks. A licensed medicine will have a Vm (veterinary medicine) number on the package.

There are products on the market that contain pesticides (such as margosa) that are sold as insect repellents for applying to cats and dogs. The ingredients are approved for use as insecticides by the Health and Safety Executive but they are not supported by evidence of effectiveness in the same way as medicines.

Products which are not licensed medicines will not usually have been tested in formal trials to prove that they are effective and safe in controlling fleas and ticks.

Short-lasting products for controlling fleas

Although these products might help, they are probably not very effective in controlling a flea infestation and are unsuitable for preventing infestations. They are all on general sale (AVM-GSL category of veterinary medicines)

Shampoos for dogs containing permethrin or pyrethrins.  Brands include Armitage, Beaphar, Bob Martin, Johnson's, Vetzyme, Wilko.

Powders for dogs (containing permethrin or pyrethrins) or cats (pyrethrins). Brands include Johnson's.

Sprays for dogs and cats containing pyrethrins or propoxur. Brands include Beaphar, Bolfo, Johnson’s.

Tablets for cats and dogs containing nitenpyram. Brands include Bob Martin, Capstar, Johnson's.

Spot-ons are applied to the skin of the cat or dog in few a spots along the back bone. The liquid spreads over the skin and remains effective for around 4 weeks which makes these products suitable for treatment and prevention. The duration of effect can be reduced by washing or bathing. Check the information on the package or in the package leaflet to see what it says about the effect of water on the product. If the dog is bathed or swims frequently, an oral formulation might be more suitable.

Non-prescription spot-ons by active ingredient

Collars have effects that last 3 to 6 months, depending on the product. The following are non-prescription collars by active ingredient.

All medicines can cause side effects (adverse effects). For example the spot-ons can cause excessive salivation or drooling if they're licked off. Spot-ons and collars may cause skin reactions (e.g. hair loss, itchiness, reddening). The package leaflet should list the reported side effects.

The trials that are done to get a marketing licence for a veterinary medicine test the safety of the product as well as how effective it is. But trials can usually only detect the most common effects. Rarer side effects often only show up when a medicine has been marketed for several years and used in lots of animals. Medicines available without a prescription have been in use for many years and so their side effects are usually well known. Knowing about rarer effects depends on people (SQPs, nurses, pharmacists, vets, pet owners) reporting them to the medicines regulator. Anyone can report a side effect to the Veterinary Medicines Directorate via the website:

Pyrethrins are naturally-occurring chemicals produced by the chrysanthemum family of plants. They have insecticidal and repellent properties. There are quite a lot of AVM-GSL products on general sale (powders, shampoos, sprays) that contain pyrethrins (e.g. Johnson's, Beaphar and Wilko brands).

Pyrethroids are synthetic versions of pyrethrins. There are two that are used in non-prescription flea and tick products (deltamethrin and permethrin). The problem with pyrethroids is that cats are more sensitive to them than dogs because their bodies cannot break them down as well as dogs.

There are products for cats that contain pyrethrins and cat collars containing permethrin. These are OK to use because they contain pyrethrins or permethrin in amounts that is safe for cats.

The danger for cats is that some spot-ons for dogs contain high concentrations of permethrin and if these are used on a cat they can cause seriously bad effects  (including muscle tremors and seizures) and even death. This can happen even if the product was not used directly on the cat but if a cat comes into contact with a dog that has recently (within about 72 hours) been treated with a permethrin spot-on.

It is important to warn people who buy a spot-on containing permethrin about the danger to cats.

There are certain things you should check before selling a flea and tick product.

  • what parasites the product is licensed to cover. Although different products might have the same ingredients, they might have different licensed uses.
  • what species it is intended for
  • that the product is suitable for the animal's age 
  • that the dose is correct (for the animal's weight)
  • how often it should be used
  • the expiry date

Remind the owner to read the information in or on the package before using it.

  • No tick repellent or tick-killing product is 100% effective. So it’s still important for pet owners to check their pet for ticks daily after being in areas likely to have large numbers of ticks (e.g. areas with long grass or ferns close to livestock or deer).
  • Some people report that a flea product has not worked. This is most likely be due to incorrect use or lack of persistence and perseverence in dealing with an infestation. It is necessary to treat all pets in the household (e.g. the cat as well as the dog) and to get rid of larvae in the home environment with environmental flea controlling products. It can take 3 months or more to get rid of an infestation.
  • In theory resistance to parasiticide drugs can develop, which would make them less effective but there is currently no evidence of resistance to pet parasiticides in the UK.
  • Spot-on products for dogs containing permethrin must never be used on cats.

Parasiticide products available only on prescription from a vet have the following features:

  • Fast flea- or tick-killing effect. Some of the products have been proven to act within hours of use. This can be important, for example if the dog or cat has flea allergic dermatitis or if the dog lives or is travelling to an area where ticks can transmit diseases.
  • Broader parasite coverage. Some prescription products protect against worms as well as fleas and/or ticks. This might be more convenient for the owner.
  • Protection against dog lungworm (Angiostrongylus vasorum) and parasites found in other countries (e.g. heartworm, mosquitoes).
  • Long-acting flea protection (up to 3 months) in tablet form. May be more suitable for a dog that is bathed or swims frequently and may be more convenient for the owner.


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