What Is Stop Lice Maximum Strength? Uses, Dosage, and What You Need to Know in 2026

Stop Lice Maximum Strength is an over-the-counter (OTC) lice-killing shampoo available without a prescription at pharmacies, grocery stores, and online. It belongs to a class of medications called pediculicides — treatments designed to kill lice parasites. Here's everything you need to know about this product for 2026.

What Are the Active Ingredients in Stop Lice Maximum Strength?

Stop Lice Maximum Strength contains two active ingredients:

• Pyrethrum Extract (equivalent to 0.33% pyrethrins): A natural insecticide derived from the chrysanthemum flower (Chrysanthemum cinerariaefolium). Pyrethrins disrupt the nervous system of lice, causing paralysis and death.
• Piperonyl Butoxide 4%: A synergist that blocks the enzymes lice use to break down pyrethrins, making the pyrethrin more effective at killing lice and reducing the potential for resistance.

This same combination appears in other well-known OTC lice treatments including RID, A-200, and Pronto.

What Is Stop Lice Maximum Strength Used For?

Stop Lice Maximum Strength is used to treat active infestations of:

• Head lice (Pediculus humanus capitis): The most common form; found on the scalp and hair. Affects 6–12 million people annually in the US, primarily school-age children 3–11 years old.
• Body lice (Pediculus humanus corporis): Found on clothing and bedding; feeds on the body. Associated with crowded or unsanitary living conditions.
• Pubic lice (Phthirus pubis, "crabs"): Found in pubic hair and other coarse body hair; typically spread by close personal contact.

Who Can Use Stop Lice Maximum Strength?

Stop Lice Maximum Strength is approved for use in:

• Adults and children 2 years of age and older

It should NOT be used without medical advice in:

• Children under 2 years of age
• People allergic to ragweed or chrysanthemums
• Pregnant or breastfeeding individuals (ask a healthcare provider first)

How to Use Stop Lice Maximum Strength: Step-by-Step

Follow these directions for treating head lice:

1. Apply to DRY hair. Unlike permethrin (Nix), pyrethrin shampoos are applied to dry — not wet — hair. Completely saturate the hair and scalp, starting behind the ears and at the back of the neck.
2. Protect your eyes. Cover eyes with a washcloth or towel. If the product gets in your eyes, flush immediately with plenty of water.
3. Leave on for exactly 10 minutes. Use a timer. Do not leave on longer than 10 minutes.
4. Rinse thoroughly. Add a small amount of warm water to form a lather, then shampoo and rinse thoroughly. Towel dry.
5. Comb out nits. Use the fine-toothed nit comb provided to remove dead lice and eggs (nits) from the hair. Part hair into sections and work from scalp to tip.
6. Repeat in 7–10 days. This is required because pyrethrins do NOT kill unhatched lice eggs (nits). A second treatment kills newly hatched lice before they can reproduce.

Important: Do Not Use a Conditioner Before Treatment

Do not use a conditioner or a shampoo containing conditioner before applying Stop Lice Maximum Strength. Conditioners coat the hair shaft and can reduce the medication's ability to penetrate and kill lice.

Will Stop Lice Maximum Strength Work? The Resistance Issue

This is the critical question for 2026. Pyrethroid resistance is widespread: approximately 77% of head lice globally carry kdr gene mutations that reduce pyrethrin and permethrin effectiveness. In areas with high resistance rates, OTC pyrethrin treatments may not eliminate lice reliably.

Signs of possible treatment resistance: live lice still moving on the scalp 24 hours after a correctly applied treatment. If you see this, contact a healthcare provider for a prescription alternative.

If OTC treatment fails, read our guide on alternatives to Stop Lice Maximum Strength for prescription options that work against resistant lice.

If you need help locating Stop Lice Maximum Strength or an alternative at a pharmacy near you, medfinder calls pharmacies and texts you which ones have your product in stock.