Know Your Head Lice Prescriptions Part I

Healthcare providers have a number of prescription medications to choose from for treating a case of head lice. Know your head lice prescriptions and don’t take for granted that all prescriptions are safe or effective.

In Part 1 of Know Your Head Lice Prescriptions, we examine three prescription products with potential side effects, some of which are quite frankly, not worth the risk of using:

  • Pyrethrin/Permethrin
  • Malathion
  • Lindane


Pyrethrin is an insecticide derived from the chrysanthemum flower.  It is the active ingredient found in Rid, an over-the-counter lice treatment product. Permethrin is a synthetically derived product that is chemically produced to act like pyrethrin in its insecticidal properties. It is the active ingredient in over-the-counter Nix “Lice Killing Cream Rinse” and various generic products.

When these products were first introduced to the market, they were in stronger dosages than what is available today. When concern first appeared over possible resistance, the manufacturers decreased the over-the-counter solutions and created prescription strengths. Today, over-the-counter solutions are comprised of 1% permethrin.  Prescriptions come in a 5% concentration.

How It’s Supposed To Work:

Pyrethrin and permethrin products are neurotoxins that attack the louse’s nervous system and can result in death.


5% is no more effective than the 1% dosage. While 20 years ago these products were almost 100% effective at killing lice, today the bugs have mutated such that head lice are now almost 100% resistant to these neurotoxins (1). The term “super lice” has become popular these days to describe this increased resistance to these products.


Permethrin has been linked to potential neurodevelopmental deficits, or abnormal behavior in children such as being anxious and withdrawn, or defiant and aggressive (2). Neurotoxicity in not only the bugs, but also the humans that these products are used on, can happen. This means that our central and/or peripheral nervous systems can be compromised when using these toxic products. Symptoms can include fatigue, pain, depression, memory loss, lung/sinus conditions, etc. From personal experience, this writer had to be prescribed an inhaler due to the breathing issues experienced after using this chemical as a form of lice treatment on the head as well as spraying in the environment.


These products are no longer effective at killing lice and nits. Combine this fact with the potential harmful side effects, they are not worth your time and money.

Buyer Beware:

At the time of writing this article, one could purchase 5% permethrin cream on eBay from a source in India that offers worldwide shipping. Take heed of their warning: “NOTE: Any sort of custom duties OR charges will be bared by buyers.” Since 5% is a prescription strength medication in the US, your shipment may never arrive here!

Malathion (Ovide)

Malathion is a chemically derived insecticide that is classified as an organophosphate.  It is used in our environment on farms, golf courses, home gardens, as a form of mosquito and Mediterranean fruit fly control, used to treat fleas on pets, etc.  It can also be prescribed to treat a case of head lice.  The brand name for malathion is called Ovide in the US, or Prioderm in Ireland.

How It’s Suppose To Work:

Malathion, and other organophosphates, work to disrupt neurotransmitters in a louse’s brain and enzymes in its nervous system, which can ultimately result in death.  Like pyrethrin and permethrin, malathion is classified as a neurotoxin.


As a neurotoxin, head lice are increasingly resistant to malathion.  No data could be found on a percentage, but the products are losing efficacy.  More importantly, the potential side effects or hazards, are alarming.


According to the Illinois Department of Public Health regarding organophosphates:

“The chemicals in this class kill insects by disrupting their brains and nervous systems.  Unfortunately, these chemicals also can harm the brains and nervous systems of animals and humans.  These chemicals stop a key enzyme in the nervous system called cholinesterase from working, and this can make people ill.” (3)

As stated above, malathion is already used as an insecticide in our environment.  Children are at higher risk of potential exposure from these environmental conditions.  They play outside more, in the dirt, put their hands in their mouths more often, and may not wash their fruit before eating it.  Malathion is already present in our bodies.

Now add one, two or three prescription head lice treatments, where you apply the prescription and leave it on the head, as directed, for 8-12 hours (!).  According to the Toxicological Profile For Malathion published by the U.S. Department of Health and Human Service, those that have been overexposed to Malathion have experienced “difficulty breathing, chest tightness, vomiting, cramps, diarrhea, watery eyes, salivation, sweating, headaches, dizziness, and loss of consciousness, and some died.” (4)

On top of the risk of neurotoxicity, malathion is extremely flammable. The CDC has the following warning: “Malathion is flammable; keep medication and wet hair away from heat sources such as hair dryers, electric curlers, cigarettes, or open flames.” (5)

A 10 year old girl in Ireland suffered severe burns to her face when the malathion head lice shampoo that she used caught fire.  Read story here.

We commonly hear from clients that have used malathion (Ovide), that it burns the scalp on application, and the fumes from the product are too overpowering.  Many cannot keep the product on their head for the recommended time.


Know your head lice prescriptions and say NO to malathion!


Lindane is another neurotoxin that is designed to kill bugs, but poses the most serious threat to humans of all prescription head lice medications on the market.  It has been banned in 52 countries worldwide, and further restricted in 33 countries.  In the US, lindane has been banned by the Environmental Protection Agency for all uses under its jurisdiction.  The Federal Food & Drug Administration, however, allows for the use in treating head lice and scabies.  While lindane cannot be sprayed on our food supply or used on any part of an animal due to its severe/fatal toxicity, it can be applied to human’s heads as a prescription head lice treatment medication under the brand name, Kwell.

The FDA cautions when using lindane shampoo and lotions even “when used as directed”, the extremely serious side effects can be severe and even fatal for young children, people weighing under 110 lbs, pregnant or nursing women, and the elderly [source: FDA website].  It can only be used once in a human’s lifetime.


Because lindane is severely toxic, NEVER use this product.  Even if it was 100% effective at killing lice and nits, which it is not (lice are increasingly resistant), our recommendation would not change.

How To Treat

So, all three of the products have a recommendation of do not use.  What should one do to treat a case of head lice?  Bottom line, there is no magical product on the market that kills lice or nits 100%.  A successful treatment means to remove every last bit of evidence from the hair.  If you leave behind two nits, one female and one male, the infestation begins again in a few weeks when those nits hatch and mature to become reproducing adults.  Toxic products are never needed in the removal process.

Call your closest Shepherd Certified lice treatment business.  They are trained professionals that are certified in all things lice.  They offer a full range of treatment services plus safe products that should you choose to treat at home, you can be successful.

About Us

Lice Spies are professionally trained and certified through the Shepherd Institute.   We provide safe, non-toxic, natural head lice checks, treatment services, DIY & preventative products at our Edmonds’ clinic. Located on the corner of Edmonds Way/SR 104 and 236th St SW in Edmonds, WA, appointments can be booked online, anytime of day or night at  Follow us on Facebook.



We’d like to acknowledge the researcher extraordinaire, Meredith Riley, founder and owner of Dandy Strands Head Lice Removal Service in Oklahoma, head lice industry consultant and research contributor to


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Posted: October 4, 2019 by Lice Spies