Pyrethrin medicines are available without a
prescription as shampoos or mousse. Apply the product to dry hair. Do not use any hair conditioner. Leave it on the hair for 10 minutes, and
then rinse it out. A second treatment is needed 9 days after the first, to kill
newly hatched lice.
How It Works
Pyrethrins kill lice and some of the eggs
(nits) at the time it is applied. Unlike permethrin, these products do not
continue to work after they have been rinsed out of the hair.
Why It Is Used
Pyrethrin medicines are a
common, useful treatment for head and pubic lice. Allergic reactions are rare.
How Well It Works
Pyrethrin products are useful against lice, but treatment
failures are getting more and more common. Some
countries have reported an increase in resistance to pyrethrin. If this occurs, your doctor can suggest other treatments (such as malathion or
All medicines have side effects. But many people don't feel the side effects, or they are able to deal with them. Ask your pharmacist about the side effects of each medicine you take. Side effects are also listed in the information that comes with your medicine.
Here are some important things to think about:
Usually the benefits of the medicine are more important than any minor side effects.
Side effects may go away after you take the medicine for a while.
If side effects still bother you and you wonder if you should keep taking the medicine, call your doctor. He or she may be able to lower your dose or change your medicine. Do not suddenly quit taking your medicine unless your doctor tells you to.
Call 911 or other emergency services right away if you or your child has:
Swelling of the face, lips, tongue, or throat.
Call your doctor if you or your child has:
Side effects of this medicine include:
See Drug Reference for a full list of side effects. (Drug Reference is not available in all systems.)
What To Think About
Do not use products containing
pyrethrins if you are
allergic to ragweed or chrysanthemums.
Itching may last for 7 to 10 days after treatment. But itching is not a reason to use the product again. Overuse of lice products (such as using the product twice when only a single use is prescribed) can irritate the skin and may increase the risk of side effects.
Medicine is one of the many tools your doctor has to treat a health problem. Taking medicine as your doctor suggests will improve your health and may prevent future problems. If you don't take your medicines properly, you may be putting your health (and perhaps your life) at risk.
There are many reasons why people have trouble taking their medicine. But in most cases, there is something you can do. For suggestions on how to work around common problems, see the topic Taking Medicines as Prescribed.
Advice for women
If you are pregnant, breast-feeding, or planning to get pregnant, do not use any medicines unless your doctor tells you to. Some medicines can harm your baby. This includes prescription and over-the-counter medicines, vitamins, herbs, and supplements. And make sure that all your doctors know that you are pregnant, breast-feeding, or planning to get pregnant.
Follow-up care is a key part of your treatment and safety. Be sure to make and go to all appointments, and call your doctor if you are having problems. It's also a good idea to know your test results and keep a list of the medicines you take.
How this information was developed to help you make better health decisions.