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A recent article alerted me to the toxicity of one of the most frequently prescribed anti-flea treatments for pets – Frontline. On the vet’s advice, I’ve always used this product on our cat and dog. I thought I’d do some research on the side effects of Frontline. Here’s what I found.

How Safe Are Flea Treatments?

Frontline contains 2 very powerful poisons – Methoprene and Fipronil. You can find lots of information on both these poisons by Googling “side effects of….”  The following is a brief summary.


Fipronil is a slow acting poison that seeps into the body of insects and stops the nervous system from working thus paralyses the insect.  Fipronil is classified by the World Health Organisation as a hazardous pesticide. It is also classified as a Class C carcinogen which means when tested it caused tumours in rats and therefore there is a theoretical risk it could cause cancer in humans.

In sufficient concentrations, it is fatal to fish, bees and birds. In humans and animals if Fipronil is ingested in sufficient quantity it can cause vomiting and seizures.


The second ingredient Methoprene is an insect growth regulator. It interrupts the normal levels of insect growth hormone thus stopping juvenile parasites such as fleas reaching maturity. If it is doing that to insects what unseen effects is it having on the insides of our pets?

Of course, both the manufacturers of Frontline and the vets say when used correctly the product is perfectly safe and to a degree that is true. Millions of pets are regularly dosed without any visible harm. I even use it myself because it works. However, having done my due diligence on Frontline it does make me think twice.

Natural Alternatives

There are of course natural alternatives for controlling parasites, that don’t do any harm to animals,  the environment or your pet.

Which do you use? Do you think the natural alternatives are as effective as the chemical treatments?

How Safe Are Flea Treatments?
Chemical flea treatments, how safe are they?
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