Fact check: What are the active ingredients in horse paste and how do they affect skin cancer?

1. What people mean when they say “horse paste” — clearing up a common confusion

The term “horse paste” commonly refers to veterinary ivermectin formulations marketed to deworm horses and sometimes repurposed by humans for skin conditions like rosacea, according to patient surveys and case reports; the active pharmaceutical ingredient in these preparations is ivermectin, not betulinic acid or similar anticancer agents ^{[1] [4]}. This is important because research cited about betulinic acid and NVX‑207 concerns equine melanoma treatment research and topical delivery into equine skin; those studies do not describe the active ingredients of commercially sold equine dewormers ^{[3] [5]}. Conflating these distinct products leads to misunderstandings about what any given “horse paste” contains and what biological effects it might have.

2. What ivermectin does in cancer models — laboratory signals, not clinical cures

Multiple recent preclinical studies have identified ivermectin’s ability to inhibit cancer cell migration, invasion, and metastasis through pathways such as Wnt/β‑catenin and integrin/FAK, and it can synergize with other anticancer agents in animal or cell models ^{[2] [6] [7]}. These findings show mechanistic plausibility for anti‑tumor activity in controlled experiments, and they motivate drug‑repurposing research. However, the available analyses are primarily in vitro or in animal models; no robust clinical trials demonstrate that topical or oral ivermectin from veterinary “horse paste” treats or prevents human skin cancers. Laboratory efficacy does not equate to safe, effective human therapy.

3. Betulinic acid and NVX‑207 — targeted research for equine melanoma, not human skin cancer

A distinct research track focuses on betulinic acid (BA) and its derivative NVX‑207, which have shown anticancer activity against equine melanoma cells and can permeate equine skin in vitro; NVX‑207 demonstrated a time‑dependent skin depot effect when compared across delivery methods, suggesting potential for topical therapy in horses ^{[3] [8] [5]}. These studies are species‑specific (equine melanoma) and experimental, and they do not equate to efficacy against human cutaneous malignancies. The existence of these compounds in translational research may contribute to mistaken beliefs that over‑the‑counter horse pastes contain the same anticancer actives.

4. Comparing the evidence: ivermectin vs. betulinic acid — different molecules, different evidence bases

Ivermectin’s anticancer evidence is broad in mechanism but limited to preclinical contexts, with several studies showing anti‑metastatic effects and pathway modulation ^{[2] [7]}. Betulinic acid and NVX‑207 present targeted topical potential for equine melanoma with permeation data and pilot therapeutic observations in horses ^{[3] [8]}. Neither body of work provides high‑quality clinical evidence supporting use of over‑the‑counter veterinary ivermectin products or experimental BA formulations as safe, effective treatments for human skin cancers. Therefore, equating laboratory findings with off‑label human use is unsupported by current data.

5. Safety, dosing, and the real‑world risks of repurposing veterinary products

Using veterinary ivermectin preparations designed for horses raises safety and dosing concerns because concentrations, excipients, and dosing scales differ substantially from approved human formulations ^{[1] [4]}. Survey data document patient use of topical equine ivermectin for rosacea, but these reports do not prove efficacy against cancer and signal potential misuse ^[1]. Off‑label self‑administration based on preclinical studies risks underdosing, toxic overdosing, allergic reactions, and delayed appropriate medical care; such harms are documented concerns in public health discussions even when not detailed in the provided analyses.

6. Gaps in the evidence — what researchers and clinicians still need to prove

Key gaps include the absence of randomized clinical trials testing ivermectin or betulinic acid formulations for human skin cancers, limited pharmacokinetic data for topical human application of veterinary products, and a lack of safety data for chronic or high‑dose use in humans ^{[6] [5]}. Existing studies are promising for mechanistic insight and equine oncology translation, but they do not establish clinical efficacy or safety for human skin cancer treatment. These omissions mean current evidence cannot justify repurposing horse paste as a cancer therapy.

7. How to interpret these findings responsibly — separating potential from practice

The research shows promising laboratory biology: ivermectin can modulate cancer‑related pathways, and betulinic acid formulations can penetrate equine skin and affect melanoma cells ^{[2] [8]}. Translating those findings into clinical use requires rigorous human trials, dose‑finding, formulation safety testing, and regulatory oversight. Until such evidence exists, clinicians and patients should treat claims that “horse paste cures skin cancer” as unsubstantiated and potentially dangerous, recognizing the difference between laboratory promise and proven medical treatment.

8. Bottom line — clear answers for people asking whether horse paste treats skin cancer

Horse paste contains ivermectin, not betulinic acid; while ivermectin and separate compounds like BA show anticancer activity in preclinical research, there is no clinical evidence that using veterinary horse paste cures or effectively treats human skin cancers, and doing so risks harm from improper dosing and delays in evidence‑based care ^{[1] [2] [3]}. Patients should consult oncology specialists and rely on approved, clinically validated treatments while researchers pursue controlled trials to clarify whether any repurposed agents warrant human use.