Nurses Advised: ASCO Cautions Against Ivermectin and Fenbendazole Use

The American Society of Clinical Oncology (ASCO) has released a formal clinical notice strongly cautioning against the use of ivermectin and fenbendazole for cancer treatment outside of regulated clinical trials.

This warning comes in response to a surge in patients self-medicating with these agents, often driven by social media misinformation and anecdotal reports of cures. For oncology nurses, who frequently serve as the primary point of contact for patient education and safety monitoring, this notice underscores a critical need for proactive inquiry into alternative therapy use to prevent toxicity and treatment interference.

The Risks: Toxicity and drug interactions

Oncology nurses must be vigilant regarding the specific clinical risks associated with these agents. Ivermectin is currently FDA-approved only for specific parasitic infections in humans, while fenbendazole remains a veterinary medication with no human approval. Patients often bypass medical oversight to purchase veterinary formulations, which may contain dangerous impurities or inconsistent concentrations.The notice highlights severe safety concerns, particularly at the high doses often suggested by non-medical influencers. Potential toxicities include:

• Neurologic and Systemic Effects: Ataxia, seizures, coma, and hypotension.
• Fatal Outcomes: In extreme cases, high-dose self-administration has led to death.
• Pharmacokinetic Interference: Both agents are metabolized via the cytochrome P450 pathway in the liver. This is a major concern for oncology nurses managing systemic therapies, as these agents can alter the metabolism of proven chemotherapy, potentially increasing toxicity or rendering life-saving treatments ineffective.

Furthermore, ASCO emphasizes the "unmeasured risk" of opportunity cost. Patients who substitute evidence-based care with these unproven agents risk uncontrolled cancer progression and preventable mortality.

Addressing the evidence gap

While some preclinical in vitro and animal studies have suggested antiproliferative effects, ASCO clarifies that these findings have not translated to human efficacy. Replicating the drug concentrations used in these laboratory settings would require human doses far exceeding established safety limits. To date, no robust, peer-reviewed clinical evidence supports the safety or efficacy of either drug for treating human malignancies.

Currently, very few human trials are underway. A phase I/II trial is investigating ivermectin in combination with pembrolizumab or balstilimab for metastatic triple-negative breast cancer, with preliminary results from nine patients presented in 2025. A randomized phase II trial (ICONIC) involving 80 patients with solid tumors is expected to start in July 2026, with results anticipated in late 2027. Until such trials establish a clear benefit-to-harm profile, these agents should not be used in clinical practice.

The nursing role: Communication strategies

Because patients often explore these therapies out of a desire for control or hope, ASCO urges the oncology care team to adopt a non-judgmental, proactive approach. Nurses are encouraged to utilize the following three strategies to manage these conversations:

• Proactive Inquiry: Nurses should routinely ask patients about their use of supplements and alternative therapies. These conversations should be approached with "respectful curiosity," acknowledging that patients may be overwhelmed or influenced by misinformation and medical mistrust.
• Educate with Empathy: It is essential to acknowledge the patient’s desire to fight their disease while using non-jargon language to explain the lack of clinical evidence and the very real risks of toxicity and drug interactions.
• Maintain Trust: Shared decision-making is vital to maintaining the therapeutic alliance. By fostering open communication, nurses can steer patients away from harmful choices without damaging the clinician-patient relationship.

"While we understand patients are looking for hope, self-medicating with unapproved veterinary or anti-parasitic drugs without their oncologist's knowledge poses a serious risk to their safety," stated Julie Gralow, MD, ASCO Chief Medical Officer, in a news release.

For oncology nurses seeking further guidance, ASCO recommends referring to their updated patient-clinician communication guidelines and utilizing patient-facing resources available through the American Cancer Society. By integrating these communication strategies into daily practice, nurses can better protect their patients from the hidden dangers of unproven alternative therapies.