Dewormer medications generally start to work within a few hours, but it may take a few days to completely eliminate all the worms depending on the type of parasite and severity of the infestation.

Timeline for Dewormer Effectiveness

• Most common dewormers begin killing worms within 12–24 hours of administration.

• Pets may start passing dead worms in their stool within the first 24–48 hours, but for some infestations, worms may continue to appear in the feces for up to 7–10 days, and occasionally up to 14 days, especially in puppies.

• In humans, medicines like mebendazole start working immediately, but it may take several days for all the worms to die and be expelled; a second dose may be needed after 2 weeks to prevent recurrence.

Factors Influencing Speed

• The type of worm (roundworms, tapeworms, hookworms, etc.) affects how quickly the medication works.

• Severity of infestation can lengthen the time needed for complete elimination.

• Specific medication and its concentration also play a role in effectiveness.

Typical Symptoms and Aftereffects

• It is normal for pets or children to have bowel movements soon after taking dewormer, and mild side effects like diarrhea or abdominal discomfort usually resolve within 24–48 hours.

• Passing dead worms in stool confirms the medication is working.

Overall, most dewormers start to work within hours, but complete expulsion of worms can take several days to two weeks depending on multiple factors.