BMA Concise Guide to Medicine & Drugs


Brand names Boots Threadworm Tablets, Ovex, Pripsen, Vermox

Used in the following combined preparations None


Drug group Anthelmintic drug

Overdose danger rating Low

Dependence rating Low

Prescription needed No (threadworm infection); Yes (Other worm infections)

Available as generic Yes


Mebendazole is used to treat various intestinal worm infestations, including threadworms, roundworms, hookworms, and whipworms. Only threadworm infection is common in the UK but the others can be acquired during travel to countries with poor sanitation. The drug works by paralysing the worms, which are then passed out in the faeces. However, mebendazole does not kill threadworm eggs, which are deposited on the skin around the anus by adult worms, and reinfection may occur by transfer of the eggs from the anus to the mouth. To prevent reinfection, the drug must be combined with hygiene measures, and all members of the family should be treated at the same time. Side effects of mebendazole are uncommon and tend to be mainly gastrointestinal. More serious side effects are rare.


Follow instructions on the label and follow hygiene measures for at least six weeks. Call your doctor if symptoms do not improve in a few days or if treatment is unsuccessful.

How taken/used Tablets, oral suspension.

Hygiene measures To prevent threadworm reinfection, wash the hands thoroughly and scrub the nails frequently, especially after going to the toilet and before eating; keep the nails short; avoid biting the nails and sucking the fingers; wash bed linen and towels to kill the eggs; do not share towels, flannels, or sponges; bathe or shower every morning; change underwear every morning; regularly vacuum and clean the house to remove any infective eggs. Oro-anal contact during sex can also cause infection or reinfection and should therefore be avoided.

Frequency and timing of doses Threadworm Single dose; can be repeated after 2 weeks if reinfection occurs. Other worms 2 x daily for 3 days.

Adult dosage range Threadworm 100mg. Other worms 200mg daily.

Onset of effect Within a few hours.

Duration of action 12-24 hours.

Diet advice None.

Storage Keep in original container at room temperature out of the reach of children.

Missed dose Threadworm Take as soon as you remember. Other worms Take as soon as you remember, but no more than 2 tablets or 10ml of liquid in 24 hours.

Stopping the drug Threadworm The drug is taken as a single dose, repeated only if necessary. It can safely be stopped when no longer needed. Other worms The 3-day course should be completed to ensure effective eradication.

Exceeding the dose A larger than recommended dose is unlikely to cause harm. A very large dose may cause dizziness, abdominal discomfort, or diarrhoea in adults. In infants, it may cause seizures. Notify your doctor.


The most common adverse effects of mebendazole are gastrointestinal symptoms, such as abdominal pain and diarrhoea, and these are most likely to occur when there is a high level of worm infestation. If these adverse effects are severe, consult a doctor. Rarely, seizures or a rash may occur; if so, stop taking the drug and seek prompt medical help.


Cimetide may increase the blood level of mebendazole and should be avoided.

Metronidazole may increase the risk of serious skin rashes when used with mebendazole. The two drugs should not be used together.


Be sure to consult your doctor or pharmacist before taking this drug if:

· You have fructose intolerance.

Pregnancy Safety in pregnancy not established. Discuss with your doctor.

Breast-feeding It is not known if the drug passes into the breast milk, so breast-feeding is not recommended. Discuss with your doctor.

Infants and children Not recommended under 2 years.

Over 60 No special problems.

Driving and hazardous work No special problems.

Alcohol No special problems.


Mebendazole is not used long term.