Mebendazole (Ovex, Vermox): threadworm and worm treatment

Mebendazole treats several kinds of intestinal worm. The NHS lists threadworms, roundworms, whipworms and hookworms. Threadworm is by far the most familiar in the UK, and it is the only one that can be treated with a pharmacy product bought without prescription.

It comes as chewable tablets or a liquid suspension, and is also sold under the brand name Vermox as well as Ovex.

For threadworms the NHS describes a single dose, which can be repeated after 2 weeks if the symptoms come back. Everybody in the household aged 2 or over should take it at the same time, because the infection is shared within a household.

Other worms are treated differently: twice a day, 10 to 12 hours apart, for 3 days. These infections, and any treatment of children aged between 6 months and 2 years, need a prescription.

Tablets can be chewed, crushed or swallowed whole with water, and must be crushed for children. Shake the liquid and use the supplied measure.

• Missed dose: take it when you remember unless the next is near; do not double up.

• Overdose: contact a pharmacist or NHS 111 promptly.

• If you are no better after several days, speak to a healthcare provider.

The NHS recommends washing hands regularly for the weeks after treatment, especially after using the toilet and before eating or preparing food. This breaks the cycle of re-infection, which is the most common reason threadworm seems to come back.

The tablet or liquid deals with the worms present at the time of the dose, so the practical aim afterwards is to avoid swallowing new eggs. Hand hygiene is the step the NHS singles out, and it applies to every member of the household, not only the person with symptoms.

Worm infections of the other types named on the NHS page, namely roundworm, whipworm and hookworm, are treated on prescription over 3 days, and a doctor decides whether any tests or follow-up are needed. If symptoms persist after the course, go back to the pharmacist or doctor rather than repeating doses at home.

Do not take mebendazole if you have had an allergic reaction to it or to similar medicines such as albendazole or ivermectin. Younger children need a prescription, and under-2s are not covered by the over-the-counter route.

The usual effects are stomach pain or discomfort, wind and diarrhoea, and it does not affect driving or using machinery.

• Call 111 for rare serious effects such as blood cell changes or liver problems.

• Call 999 for seizures or anaphylaxis.

Speak to a doctor or pharmacist before using mebendazole in pregnancy; it may be used if the benefits outweigh the risks. It can be used while breastfeeding, but check with a healthcare provider.

The NHS names metronidazole and cimetidine as medicines to check. There are no food or alcohol restrictions. Suspected side effects can be reported through the Yellow Card scheme.