How Long Does It Take For A Puppy Wormer To Work?

Intestinal worms pose a serious threat to your puppy's health and are extremely common--98 percent of puppies are born with worms they have contracted from their mother in utero. Puppy wormer medications effectively treat worms, but it's important to administer them for long enough and at the proper intervals to kill all of the parasites.

Defocused Shot of a Labrador Puppy Carrying a Slipper in its Mouth
Puppy running with slipper
credit: Digital Vision./Photodisc/Getty Images

Multiple Doses

Vet examining puppy
Vet with puppy
credit: Comstock Images/Comstock/Getty Images

Puppy worming medications are readily available and most are effective and quick-acting, but they can only kill adult intestinal worms--not the eggs that worms lay or newly hatched worms. For this reason, one dose of puppy wormer is not enough to completely rid your puppy of parasites. You will need to administer three or four doses over a period that will typically range from six weeks to two months.

Two-Week Intervals

Boy with Yellow Lab Puppy
Boy holding puppy
credit: Ryan McVay/Photodisc/Getty Images

The second, third, and fourth doses of puppy wormer need to be timed to reflect the life cycle of the worm--since medicine is only effective against adult worms, time must be allowed for the eggs laid by the first generation of worms to hatch and mature. This takes about two weeks. Administer the second cycle of medication two weeks after the first, the third cycle two weeks later, and, if you want to be absolutely sure your puppy's worms are gone, a fourth cycle two weeks after that.

Ensuring Your Dog's Health

Dog on sofa
Puppy on couch
credit: Chris Amaral/Digital Vision/Getty Images

Three rounds of puppy wormer are necessary to rid your puppy of parasites; four rounds will be even more effective and may be necessary in cases of serious infection. After you have administered the final dose and given it two weeks to take effect, you should take your puppy to the vet for a microscopic fecal exam. The vet will take and examine a stool sample to verify that no worms are present. If worms are found, one more dose of puppy wormer should be given.