Who should avoid taking ivermectin due to risk of side effects?
This fact-check may be outdated. Consider refreshing it to get the most current information.
Executive summary
Ivermectin should be avoided by people with known hypersensitivity to the drug, by pregnant women unless benefits clearly outweigh risks, by those using veterinary formulations, and by people with specific infections or drug interactions that raise the risk of serious adverse events (notably heavy Loa loa infection and concurrent CYP3A4/P‑glycoprotein inhibitors) [1] [2] [3] [4]. Additional high‑caution groups include the very young (under 15 kg), elderly with organ impairment, and patients on anticoagulants or interacting medicines because of bleeding, neurologic, or pharmacokinetic risks [5] [6] [7].
1. Hypersensitivity and absolute contraindications — when it’s simply off the table
The only absolute contraindication consistently noted by product labeling and drug references is hypersensitivity to ivermectin or any component of the formulation, meaning people with prior allergic reactions should not take it (Stromectol labeling and summaries) [1] [2]. Reports and drug information pages reiterate that signs of severe allergic reaction—hives, facial swelling, difficulty breathing—require emergency care (Drugs.com) [8].
2. Pregnancy and breastfeeding — caution from regulators and labels
Regulatory labeling and FDA materials advise that ivermectin should not be used in pregnancy because safety has not been established, and that breastfeeding requires weighing maternal benefit against potential newborn risk since ivermectin is excreted in human milk in low concentrations (Stromectol label; FDA summaries) [2] [9]. Several references therefore treat pregnancy as a high‑caution state rather than routine use [1] [2].
3. Children and weight limits — the lower bound matters
Oral ivermectin dosing is weight‑based and many authorities state it is not confirmed safe or effective in children weighing less than 15 kg, making that group one to avoid unless directed by specialist guidance (Mayo Clinic; Medical News Today) [5] [10]. Pediatric guidance also highlights that infants and very small children have different blood–brain barrier characteristics, which can raise concern for central nervous system effects (American Academy of Pediatrics summarized) [11].
4. Elderly and organ impairment — dose adjustments, not blind prescribing
Although geriatric‑specific problems that limit usefulness are not universally identified, elderly patients are more likely to have age‑related liver, kidney, or heart problems that can slow metabolism and raise ivermectin exposure, calling for caution and potential dose adjustment (Mayo Clinic; Medical News Today) [5] [10]. Drug references emphasize assessing hepatic and renal function before prescribing in older adults [5].
5. Drug interactions — anticoagulants, CYP3A4 and P‑glycoprotein inhibitors are red flags
Post‑marketing reports and interaction databases note rare increases in INR when ivermectin was co‑administered with warfarin and list multiple drugs (eg, CYP3A4 or P‑glycoprotein inhibitors) that can raise ivermectin levels and therefore the risk of toxicity, so people on such medications warrant avoidance or close monitoring (Medscape; DrugBank; Medical News Today) [7] [12] [10]. Reviews have also linked coadministration of CYP3A4 inhibitors to greater blood–brain barrier penetration risk [11] [4].
6. Neurologic risk and Loa loa co‑infection — rare but catastrophic in specific settings
Serious neurologic adverse events including encephalopathy, ataxia, coma and death have been reported notably in people with very high densities of Loa loa microfilariae and possibly in others when interacting drugs or genetic polymorphisms increase CNS exposure; public health literature and reviews therefore advise avoiding ivermectin in persons with heavy Loa loa infection (mf >30,000/mL) and exercising caution in people from endemic areas (ScienceDirect; PMC review; Wikipedia summary) [3] [4] [11].
7. Veterinary products and overdose risk — a preventable danger
Regulators and drug information pages repeatedly warn against using animal ivermectin products for humans: veterinary formulations are more concentrated, not formulated for human dosing, and have caused overdoses with nausea, hypotension, neurologic effects, seizures, coma and death when misused (Drugs.com; FDA; MedlinePlus) [8] [9] [6]. The public‑health emphasis is clear: do not substitute animal products.
8. Where the evidence is limited and why individualized medical advice matters
Available sources agree that many risks are context‑dependent—dose, co‑infections, co‑medications, age, pregnancy and organ function all alter safety—so blanket statements can mislead; clinical judgment, screening (for strongyloidiasis or loiasis where relevant), and legitimate prescriptions filled through pharmacies are the repeatedly recommended safeguards (MedlinePlus; Drug references; clinical reviews) [6] [12] [4]. Where source material is silent about a specific individual scenario, this reporting does not speculate and defers to clinicians.