What Kind of Bugs Does Comfortis Kill in Dogs?

Comfortis starts killing fleas within half an hour of application.
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Unlike some canine pest-control products that get rid of fleas and ticks, Comfortis kills only fleas. You give it to your dog each month in chewable pill form, so it's easier to administer than common spot-on treatments. For best results, start giving your dog Comfortis at least a month before flea season starts in your region, continuing until flea season is finished. In many regions, vets recommend flea preventive year-round. Comfortis is only available by veterinary prescription.


The active ingredient in Comfortis is spinosad, derived from microbes occurring naturally in soils. Spinosad works by attacking fleas' nervous systems, causing death. It can be used on dogs who are more than 3.3 pounds and at least 14 weeks old. While most dogs tolerate spinosad well, it can cause vomiting in some canines. Other potential side effects include appetite loss and lethargy.

Fast Action

Once your dog consumes a beef-flavored Comfortis tablet, it takes about a half-hour for the initial fleas on his body to start dying. Virtually all of them are dead within four hours. Effectiveness lasts for approximately one month. To control the flea population, you must treat every dog or cat in your house. Comfortis is also available in feline versions.