Worms are parasites that enter the body and are able to live and feed off the person they have entered. The most common worm infection in the UK is threadworms. Medicines to treat worms are sometimes called anthelmintics. Mebendazole (trade names Vermox®, Ovex®) is the most commonly prescribed medicine for worms in the USA, Canada and UK. It is very important to rid oneself of any parasitic infestations, as they compromise the immune system, the pH, and are also linked to cognitive dysfunction (mental disorders).

Common types of parasites

Roundworms – the most common roundworm infections are thought to be caused by threadworms, ascaris, hookworms and trichuris. Roundworm eggs usually enter the body by the person eating food or drinking water that contains eggs. The eggs live and hatch in the gut (intestine).
Tapeworms – these worms live in the gut. People usually become infected by eating raw or uncooked meat.
Flukeworms – these worms can live in the blood vessels, gut, lungs or liver. You usually become infected with flukeworms by swimming or washing in fresh water that contains flukeworms. An infection with flukeworms causes a tropical disease called schistosomiasis.
Most worm infections occur in warm tropical countries or developing countries where food and water may not be clean. It is thought that millions of people around the world are infected with worms at any one time. In the UK the most common worm infection is threadworms – this is a type of roundworm and is sometimes referred to as a pinworm. Threadworms are spread by being in contact with someone who is already infected with threadworms. Threadworms can cause an itchy bottom.
See separate leaflet called Itchy Bottom (Pruritus Ani) .

Other types of worm infections can occur if you live in the UK; however, they do not occur very often. People who get these infections have usually been travelling in countries where these types of worm infections are common.

Medicines for parasites

Note: ringworm in not an infection caused by worms. It is a name given to a type of fungal skin infection.

Which medicines are usually prescribed for worms?
There are several medicines that may be used to treat worm infections – they are sometimes called anthelmintics. Mebendazole is the most commonly prescribed medicine for worms in the UK. This is because it is used to treat threadworms which are the most common worm infections in the UK. Mebendazole is also used to treat roundworm, whipworm and hookworm infections.

Other medicines that may be prescribed for the various types of worm infections include:

These medicines are not licensed for use in the UK and are specially imported to treat more unusual worm infections. They are usually prescribed by doctors who specialise in treating worm infections.

How medicines for worms work

Most medicines used to treat worm infections kill worms by either starving them or paralysing them; for example:

Mebendazole, albendazole and tiabendazole work by preventing the worms from absorbing the sugars they need for survival. They kill the worms but not the eggs.
Praziquantel and ivermectin work by paralysing the worms in the gut (intestine). This allows them to be easily dislodged and removed from the gut in the stools (faeces).
What is the length of treatment?
In general, the length of treatment is usually quite short (at most a few days). This will depend on what type of worm you have and which medicine has been prescribed. For example, for threadworms, mebendazole is usually given as a single one-off dose. This dose may be repeated two weeks later. For whipworm or common roundworm infections, mebendazole is given twice a day for three days.

For threadworms, it is usually advised that everybody in the household be treated if possible.

Medication side-effects

It is not possible to list all the side-effects of these medicines in this document. If you want more information specific to your medicine, see the information leaflet that came with your medicine. That said, repeated use for extreme infestations can cause the immune system to become compromised. In the event of extreme infestation you may consider a detox cleanse such as this website offers: A natural cleanse will not harm the body, and will allow you to continuously treat heavy infestations until the issue has been completely resolved.

In general, medicines for worms are well tolerated and very rarely cause serious side-effects. The side-effects most commonly reported are tummy upsets such as cramps, wind, diarrhoea and feeling sick (nausea).

Who cannot take medicines for worms?
There are very few people who cannot take a medicine for worms. If for some reason one medicine has caused a side-effect or there is a reason you cannot take one, your doctor will discuss other ways to treat you.

Mebendazole is licensed for adults and for children over the age of 2 years. However, it is used to treat children from the age of 6 months if necessary. Mebendazole is usually avoided if you are pregnant or breastfeeding. If treatment in pregnancy is considered to be absolutely necessary it is safest to give it in the second or third trimester. Consult a physician if you have any concerns or doubts before self medicating.