Fact check: What are the common side effects of ivermectin at high dosages in humans?

1. What the case reports are loudly reporting — vivid neurologic and visual problems

Multiple independent case reports from 2023 describe patients who self-administered supratherapeutic ivermectin and developed acute neurologic syndromes: decreased sensorium, restlessness, complex visual hallucinations, confusion, and ataxia. These reports identify a consistent pattern of CNS involvement that often presented within hours to days of ingestion and resolved with supportive care, suggesting a dose‑related toxidrome affecting the central nervous system ^{[2] [4] [5]}. One report emphasizes the first locally documented overdose in the Philippines, underscoring that neurologic symptoms are the predominant clinical signal in human overdoses ^[5].

2. Visual disturbances documented at very high single doses — reversible but striking

A 2023 case series specifically described reversible visual alterations after a single 180 mg dose of ivermectin, including blurred and darkened vision that began about six hours after intake and resolved within a day. These events were transient in the reported cases but illustrate that high single doses can produce sensory disturbances that are clearly perceptible to patients and temporally linked to ingestion ^[1]. The reversible nature in these case reports does not preclude more severe or prolonged visual effects in other circumstances or with different co‑factors.

3. Extreme overdoses can cause marked CNS depression and require supportive treatment

A 2024/2023 case from Cameroon and other reports document ingestion levels many times above recommended therapeutic doses, producing central nervous system depression, dizziness, ataxia, headache, and prolonged visual problems, with recovery following symptomatic care including activated charcoal and monitoring. These cases demonstrate that exceptionally high exposures can produce life‑threatening CNS depression, but supportive care has proven effective in reported survivors ^{[6] [2]}.

4. Animal studies warn of tissue injury and inflammatory changes at toxic levels

A June 2025 rat study found significant histological and morphological changes in brain and skin tissues after acute ivermectin toxicity, along with oxidative stress, disrupted P‑glycoprotein expression, and inflammatory cytokine alterations. These findings indicate mechanistic pathways (oxidative stress, BBB and transport protein disruption, inflammation) that could underpin the neurologic and cutaneous signs seen in humans at high doses, though species differences limit direct translation ^[3]. The animal data raise concern that repeated or extreme exposures might produce structural injury beyond transient symptoms.

5. Systematic reviews highlight safety data gaps at high doses in humans

A systematic review and meta‑analysis on the safety of high‑dose ivermectin (publication dated 2020) provides context that higher-than-standard doses have been studied, but it does not catalogue a comprehensive list of common high‑dose side effects and indicates that high‑dose safety evidence in humans is still incomplete. This gap contrasts with abundant case‑report signals and the emerging animal toxicology literature, pointing to a mismatch between limited systematic human safety data and real‑world overdose observations ^[7].

6. Treatments and cross‑species lessons — symptomatic care, charcoal, and experimental approaches

Reported human management has centered on supportive care and activated charcoal, with successful recoveries in documented cases, while veterinary literature and experimental animal work explore options like intralipid therapy and adjuncts (e.g., antioxidants, flumazenil in animal models). These heterogeneous approaches indicate no standardized antidote for severe ivermectin toxicity in humans, and they underscore the experimental nature of some interventions based on animal or veterinary precedent ^{[8] [3] [5]}.

7. Putting the evidence together — what is common vs. what is rare or theoretical

Across the reports, the most commonly observed effects at high or supratherapeutic doses are neurologic symptoms and visual disturbances, often reversible with supportive care. More severe outcomes (profound CNS depression, structural brain injury suggested in animals) appear in extreme overdoses or in preclinical models and are less commonly documented in humans. The evidence base is dominated by case reports and animal studies, leaving substantial uncertainty about incidence rates, dose thresholds, and co‑factors that predict worse outcomes ^{[1] [2] [3]}.

8. What’s missing and what practitioners should watch for

Key gaps include robust dose‑response human trials, standardized reporting of adverse events at defined high doses, and systematic long‑term follow‑up after overdose. Clinicians should monitor for CNS depression, altered mental status, visual changes, ataxia, and signs of systemic inflammation, and public health messaging should stress the lack of evidence for unapproved high‑dose use. The current literature supports caution: high doses carry demonstrable neurologic and visual risks, with animal data suggesting potential for deeper tissue injury at toxic exposures ^{[7] [4] [3]}.