Does ivermectin horse paste on the scalp kill head lice?

1. What the evidence shows about ivermectin for head lice in humans

Randomized and nonrandomized studies, systematic reviews and product data establish that ivermectin works against human head lice: topical ivermectin 0.5% lotion increases chloride conductance in louse muscle, causing paralysis and killing lice with a single application and has superior cure rates versus vehicle control by day 15 ^[1]; oral ivermectin has been tested in multiple trials across countries and is considered an option comparable to or sometimes superior to topical treatments, particularly when resistance or treatment failure is an issue ^{[3] [6]}.

2. Why formulation and route matter: human lotion/tablets versus veterinary paste

Mechanism studies and clinical approvals are based on human formulations and controlled doses—topical lotion applied briefly to dry hair, and oral tablets dosed by body weight—so efficacy and safety data derive from those preparations ^{[1] [7] [8]}. Veterinary pastes and pour‑ons are manufactured with different concentrations, excipients, and dosing intended for large animals; those differences mean animal products may not deliver the same scalp exposure, penetration, or safety profile in humans ^{[9] [10]}.

3. The murky evidence and risky DIY solutions among users

Anecdotes and internet guides describe people diluting or mixing horse paste into conditioners and applying it to human hair to save money or avoid prescription costs ^[11], and forum threads reflect confusion about why some animal ivermectin formulations (injectable, pour‑on) are effective against animal lice while oral paste may not act topically ^[12]. These are anecdotal and not clinical evidence; published trials and regulatory approvals concern human-specific formulations, not repurposed veterinary pastes ^{[1] [3]}.

4. Safety and poison‑control warnings about veterinary ivermectin use in people

Toxicity reports and poison‑control advisories document harms from people ingesting veterinary ivermectin products—severe gastrointestinal, neurological, or other adverse effects have been reported when animal formulations were used improperly by humans—and public health guidance explicitly advises not to take veterinary products intended for animals ^[5]. Human dosing (oral 200–400 μg/kg in trials; topical 0.5% lotion protocols) is calibrated to human pharmacology and monitored in clinical studies ^{[3] [7]}.

5. Practical conclusion: does horse paste on the scalp kill head lice?

Direct clinical evidence that applying ivermectin “horse paste” to a human scalp reliably kills head lice is absent from the medical literature provided; human-formulated topical ivermectin does kill lice and is proven effective ^{[1] [2]}, and oral ivermectin is an established off‑label option in trials ^{[3] [4]}, but veterinary paste is not equivalent and carries documented safety risks if misused ^{[5] [10]}. Thus, while ivermectin as a molecule kills lice in validated human formulations, using horse paste on the scalp is an unproven and potentially unsafe DIY approach rather than a medically recommended treatment ^{[1] [5]}.

6. Alternatives, agendas, and what to do next

Clinically recommended options include OTC permethrin or pyrethrins where effective, prescription topical products (including ivermectin lotion 0.5%), and supervised oral ivermectin in selected cases; cost, access, and resistance concerns drive people toward off‑label or veterinary workarounds, but those motivations create a hidden agenda for DIY fixes that bypass safety data ^{[6] [7]}. The reliable course supported by the evidence is to use approved human formulations or see a clinician for oral ivermectin if needed, rather than self‑applying veterinary pastes whose scalp efficacy and safety have not been demonstrated ^{[1] [5]}.