Vermox (mebendazole) starts working right away, but it takes several days to kill all the worms in your system. Most people feel fine after taking it, though mild stomach-related side effects are possible. What matters just as much as the pill itself is what you do in the days and weeks that follow to prevent reinfection.
How Quickly Vermox Works
The medication begins killing parasites immediately after you take it. However, it doesn’t wipe them all out at once. It can take several days for all the worms to die, and you may not notice a dramatic change in symptoms right away. For pinworm infections specifically, the itching around the anus (caused by eggs laid on the skin) often lingers for a few days after treatment as your body clears remaining eggs and dead worms.
You can take Vermox with or without food. A high-fat meal increases how much of the drug gets absorbed into your bloodstream (up to four times as much at peak levels), but since the medication works primarily inside your digestive tract rather than through your blood, eating or not eating before your dose doesn’t meaningfully change how well it works against intestinal worms.
Common Side Effects
Clinical trial data covering more than 6,200 patients found that the most frequently reported side effects are digestive: stomach pain, diarrhea, nausea, vomiting, gas, and loss of appetite. These are typically mild and short-lived. Some people also develop a skin rash.
Serious reactions are rare. Postmarketing reports have included dizziness, convulsions, liver inflammation, and severe allergic reactions, but these come from voluntary reporting across many years and various dosing regimens, making them uncommon in the context of a standard one- or two-dose treatment for pinworms.
What You Might See in Your Stool
It’s normal to see dead or dying worms in your stool in the days after taking Vermox. Pinworms are small, white, and thread-like, roughly the length of a staple. Some people never notice anything in the toilet, and that’s also normal. The absence of visible worms doesn’t mean the medication failed. Many worms are partially digested before they pass.
The Second Dose
For pinworm infections, treatment involves two doses. The CDC recommends taking the second dose two weeks after the first. The standard amount for both adults and children is 100 mg per dose. This second round is important because Vermox kills adult worms but doesn’t reliably destroy their eggs. Any eggs that survived the first dose can hatch within two weeks, and the follow-up dose catches those newly hatched worms before they mature enough to lay more eggs. Skipping the second dose is one of the most common reasons people end up reinfected.
For other types of worm infections, your doctor may recommend additional doses at three-week intervals. If your symptoms haven’t improved after the full course of treatment, or if they get worse, that’s worth a follow-up visit.
Hygiene Steps That Actually Matter
The pill handles the worms already inside you, but pinworm eggs can survive on surfaces, clothing, and bedding for two to three weeks. Without careful hygiene during the treatment window, reinfection is easy and common. The CDC recommends maintaining strict hygiene measures for at least two weeks after the last dose.
Here’s what makes the biggest difference:
- Handwashing: Wash thoroughly with soap and warm water after using the toilet, after changing diapers, and before handling food. This is the single most effective step.
- Morning showers: Bathe every morning to wash away eggs deposited overnight around the anus. Showers are better than baths, since tub water can spread eggs. Children should bathe separately rather than together.
- Clean underwear daily: Change underwear each morning after bathing. Change pajamas daily as well.
- Hot-water laundry: Wash all underwear, pajamas, towels, and bedding in hot water (at least 130°F) and dry on high heat. Don’t shake these items before washing, since that can release eggs into the air.
- Short, clean nails: Trim fingernails short and scrub underneath them after treatment. Eggs collect under nails when someone scratches, and nail-biting is a direct route to reinfection.
- Don’t share washcloths or towels: Use fresh ones each time.
Everyone in the household should follow these steps, not just the person who was treated. Pinworm spreads easily between family members, and it’s common for doctors to recommend treating the entire household at once, even if only one person has confirmed symptoms.
Signs the Infection Has Cleared
The clearest sign that treatment worked is the disappearance of symptoms, particularly nighttime itching around the anus. This typically fades within a week of the first dose but can occasionally take until after the second dose to fully resolve. If itching returns more than a few days after your second dose, or if you spot live worms again, you may need another round of treatment.