Does Hartz kill roundworms?

Dr. Marie replied:

Thanks for an interesting question!

Hartz flea drops are not supposed to treat roundworms (which is most likely what you saw). The ingredients in Hartz flea and tick drops are mostly phenothrin and some methoprene. Both of these have some effectiveness against fleas. (I say some because I find that these products do not work well for fleas.)

There is no claim on the label that they work for intestinal parasites. I did some research for you to see if there was any connection but could not find any.

However, my theory is that the ingredients do have some effect on roundworms. Many of the topical medications do get absorbed through the skin and can have systemic effects as well.

It is definitely a good idea to repeat a treatment with a dewormer that is meant for roundworms as there may still be more there. You will also want to repeat it in 10-14 days to make sure that you cover all the life stages.

As an additional note, I really don't recommend over the counter flea products like Hartz. I have seen so many cases where they don't work and in some cases they can be toxic especially if applied to a young puppy or to a cat.

I hope that helps!

Dr. Marie

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