mebendazole over the counter typically begins working within a few hours of ingestion, but the full effect may take a few days. For common infections like pinworms, most worms are killed within 24 to 72 hours after a single 100 mg dose. Infections with roundworms or whipworms may require a three-day course (100 mg twice daily), with noticeable symptom improvement within a few days. Stool should return to normal within a week.
