What are the known toxic effects and symptoms of ivermectin overdose in humans?

1. What the public-health agencies say: short, strong warnings

U.S. public-health agencies have repeatedly warned that overdosing on ivermectin can cause nausea, vomiting and diarrhea, hypotension, allergic reactions (itching, hives), dizziness, ataxia (balance problems), seizures, coma and even death; the FDA and CDC issued broad cautions during COVID-era misuse and rising poison‑control calls ^{[2] [1]}.

2. Common early symptoms seen in poison-center reports

Poison-control data cited by the CDC and news outlets show early, common manifestations include gastrointestinal symptoms (nausea, vomiting, diarrhea) and milder neurologic complaints such as dizziness, somnolence or confusion — signs that prompt calls to poison centers or clinicians ^{[1] [4]}.

3. How severe neurologic toxicity occurs — biology and special risks

Severe CNS toxicity is biologically plausible because ivermectin can affect GABA and other CNS receptors if it reaches brain tissue; normally P‑glycoprotein (ABCB1/MDR1) at the blood–brain barrier pumps ivermectin out, but genetic defects or very high exposures can overwhelm this protection, producing encephalopathy, coma and seizures as documented in case reports ^{[3] [5]}.

4. Veterinary formulations and dose mistakes: why “you are not a horse” matters

Public warnings stressed that veterinary ivermectin products are often far more concentrated and formulated for large animals; taking those products has produced many of the overdose cases and hospitalizations reported during periods of non‑medical use ^{[1] [6]}.

5. Who is especially vulnerable

People with certain conditions (for example, high Loa loa microfilaremia after mass ivermectin dosing) and individuals with loss‑of‑function variants in ABCB1 are at elevated risk of severe adverse events; veterinary‑level dosing or interactions with other drugs that inhibit CYP3A4/P‑glycoprotein can also raise brain exposure ^{[3] [5]}.

6. Reported severe outcomes and fatalities

Health agencies and medical reporting note hospitalizations and rare deaths from overdose; news reporting to the CDC and FDA documented cases requiring hospitalization and, in extreme cases, fatalities tied to misuse or very large doses ^{[1] [2]}.

7. Clinical guidance: what to do if overdose is suspected

Medical sources advise calling poison control (800‑222‑1222 in the U.S.) or seeking emergency care for severe symptoms; clinicians manage supportively (airway, seizure control, fluids, blood‑pressure support) because there is no widely used specific antidote in routine practice ^{[4] [2]}. Memorial Sloan Kettering and other clinical centers likewise stress immediate medical evaluation for suspected overdose ^[7].

8. Limits of available reporting and competing perspectives

Most authoritative sources (FDA, CDC, major medical centers) agree on the list of overdose symptoms and the need for urgent care ^{[2] [1] [7]}. Some secondary reviews and non‑peer outlets emphasize ivermectin’s overall low toxicity at approved doses or speculate about very high LD50s in animals, but those data do not contradict human clinical reports of severe adverse events from misuse; available sources do not mention a safe threshold for ingesting veterinary formulations ^{[8] [9]}.

9. What this means for patients and policymakers

Given documented poison‑center surges and hospitalizations tied to misuse, the practical takeaway for clinicians and the public is to avoid non‑prescribed ivermectin (especially veterinary products), to treat any suspected overdose as a medical emergency, and to recognize that genetic or drug‑interaction factors can markedly raise CNS risk ^{[1] [4] [3]}.

Limitations: this summary uses public‑health alerts, clinical reviews and case reports from the provided sources; it does not provide exhaustive toxicology dose–response tables or personalized medical advice — for those, contact a clinician or poison control as noted ^{[4] [2]}.