Permethrin Drug Interactions: What to Avoid and What to Tell Your Doctor

If you've been prescribed permethrin and you're on other medications, you're probably wondering whether there are any interactions to worry about. The good news: permethrin has one of the cleanest interaction profiles of any prescription medication.

Does Permethrin Have Drug Interactions?

No. Permethrin topical has no known severe, serious, moderate, or mild drug interactions with other medications. This is confirmed by multiple clinical pharmacology references, including the prescribing information for permethrin 5% cream and established drug interaction databases.

The reason is straightforward: less than 2% of topically applied permethrin is absorbed through intact skin. The amount that reaches the bloodstream is too small to cause clinically meaningful interactions with other drugs you may be taking orally or intravenously.

Why Are Drug Interactions Unlikely with Permethrin?

Interactions between drugs typically occur because one drug affects how the body absorbs, metabolizes, or eliminates another. With permethrin:

Minimal systemic absorption: In clinical studies with radiolabeled permethrin, plasma concentrations were undetectable after standard topical application. There simply isn't enough drug in the bloodstream to compete with or affect other medications.

Rapid metabolism: What little permethrin does enter the system is rapidly broken down by esterases in the skin and liver into inactive metabolites and excreted in urine. It is not stored in tissues.

Topical-only use: Oral or injectable drugs you're taking are very unlikely to affect how permethrin works on the skin surface, and permethrin applied to the skin does not meaningfully affect systemic drug levels.

What Should You Tell Your Doctor Before Using Permethrin?

Even though formal drug interactions are not a concern, you should always tell your doctor or pharmacist:

Allergies to pyrethrins, chrysanthemums, or ragweed. Permethrin is a synthetic pyrethroid; people allergic to natural pyrethrins (found in chrysanthemum-based pesticides) or with chrysanthemum allergies should not use it. Some sources suggest caution in ragweed-sensitive individuals.

All medications you're taking, including OTC drugs, vitamins, and supplements — even if interactions are unlikely. This is good practice for any new medication.

Pregnancy or breastfeeding. Permethrin is generally considered safe in both (it is the CDC-preferred treatment for scabies in pregnancy), but your provider should know.

Broken, inflamed, or infected skin. If the skin barrier is severely compromised, absorption may be slightly higher. Discuss this with your provider if you have open sores or severe dermatitis.

Any history of seizure disorders. There are rare post-marketing reports of seizures associated with permethrin use (none confirmed causal), but patients with known seizure disorders should inform their provider.

What About Using Other Topical Products Alongside Permethrin?

Avoid applying other topical medications, creams, or lotions to the same area while permethrin is on the skin. This is not because of a drug interaction per se, but because:

Other substances may interfere with permethrin's contact time with the skin or mites.

Certain emollients or oils may slightly increase skin absorption of permethrin.

For head lice treatment, do NOT use conditioner on hair before applying permethrin — it coats the hair shaft and significantly reduces the lotion's effectiveness.

Is Permethrin Safe to Use with Oral Ivermectin?

Yes. Combination therapy with topical permethrin and oral ivermectin is actually sometimes prescribed for crusted (Norwegian) scabies or difficult-to-treat cases. Clinical studies have found that the combination achieves the highest cure rates for scabies and is well-tolerated. There are no known interactions between the two.

Bottom Line

Permethrin has no known drug interactions when used topically. It is safe to use alongside virtually any medication. The main contraindications are allergy to pyrethrins and use in infants under 2 months. For information on side effects, see our guide to permethrin side effects. If you're having trouble finding permethrin at a pharmacy near you, medfinder can help.