Can ivermectin cause psychosis?

Ivermectin Does Not Cause Psychosis at Therapeutic Doses

Ivermectin does not cause psychosis when used at approved therapeutic doses for parasitic infections, but psychosis and other serious neurological adverse events can occur with supratherapeutic doses or in specific high-risk situations.

Understanding the Risk Profile

Therapeutic Doses Are Safe

The FDA-approved dosing for ivermectin (typically 200 mcg/kg for parasitic infections) has an established safety profile 1. Multiple treatment guidelines from the CDC and WHO recommend ivermectin as first-line therapy for scabies, strongyloidiasis, and onchocerciasis without listing psychosis as an expected adverse effect 2.

When Psychosis Can Occur

Supratherapeutic Dosing:

• Case reports document acute psychosis in patients taking massive overdoses of ivermectin, particularly veterinary formulations 3, 4, 5
• A 2022 case series found that patients taking veterinary formulations ingested significantly higher doses and developed altered mental status more frequently than those taking prescription tablets 5
• Median toxic doses in these cases were substantially higher than therapeutic dosing, with some patients taking daily doses meant for large animals

Specific High-Risk Scenarios: The most critical risk factor is co-infection with Loa loa (African eye worm) in patients being treated for onchocerciasis:

• Patients heavily infected with Loa loa may develop serious or even fatal encephalopathy following ivermectin treatment 1
• This syndrome includes mental status changes, confusion, lethargy, stupor, seizures, or coma 1
• Risk increases dramatically when Loa loa microfilarial density exceeds 8,000-30,000 mf/mL 6
• The FDA label specifically warns about this risk and recommends pretreatment assessment for loiasis in patients with significant exposure to endemic areas of West or Central Africa 1

Mechanism and Clinical Presentation

Why Neurotoxicity Occurs

Ivermectin typically does not cross the blood-brain barrier in humans 1. However, neurotoxicity can occur when:

• Extremely high doses overwhelm normal protective mechanisms
• In Loa loa co-infection, the mechanism involves the parasite rather than direct drug toxicity
• Potential genetic factors (MDR-1 gene polymorphisms) may allow increased CNS penetration in some individuals 7

Clinical Features of Ivermectin Neurotoxicity

When toxicity occurs, the presentation includes 1, 4, 5:

• Altered mental status and confusion
• Visual hallucinations (complex visual hallucinations reported in overdose cases)
• Ataxia, tremors, and seizures
• Decreased level of consciousness progressing to stupor or coma
• Gastrointestinal symptoms (nausea, vomiting, diarrhea)

Critical Clinical Distinctions

COVID-19 Misuse Context

Recent case reports of ivermectin-induced psychosis predominantly involve patients self-medicating for COVID-19 with inappropriate doses 3, 4, 5. The IDSA strongly recommends against ivermectin for COVID-19 (strong recommendation, moderate certainty) 8, and the WHO guidelines echo this position 9. These cases represent drug misuse rather than adverse effects at therapeutic dosing.

Combination Therapy Considerations

One case report documents psychosis with albendazole-ivermectin combination therapy 10, suggesting potential drug-drug interactions may increase risk, though this remains poorly characterized.

Practical Management Approach

Before Prescribing Ivermectin

1. Screen for Loa loa exposure: Any patient with travel to or residence in West or Central Africa requires pretreatment assessment before ivermectin administration 1
2. Verify appropriate indication: Ensure ivermectin is indicated for a parasitic infection, not off-label use
3. Calculate correct dosing: Standard dose is 200 mcg/kg, not mg/kg
4. Review medication list: The FDA label notes potential interaction with warfarin (increased INR) 1

Patient Counseling

• Take on an empty stomach with water 1
• Do not use veterinary formulations
• Avoid exceeding prescribed doses
• Report immediately: confusion, visual changes, difficulty walking, or altered consciousness

If Psychosis Develops

• Discontinue ivermectin immediately
• Supportive care is primary treatment 1
• Consider activated charcoal if recent ingestion (within hours) 4
• Most cases resolve within 24-48 hours with supportive care 4
• Benzodiazepines (clonazepam) have been used successfully for drug-induced psychosis 10

Special Populations

Pediatric patients <15 kg: Safety not established; avoid use 1

Pregnancy: Classified as "human data suggest low risk" but should be avoided unless benefit outweighs risk 2

Elderly or debilitated patients: One study showed increased mortality in this population, though not confirmed in subsequent reports 2

Severe liver disease: Safety of multiple doses unknown 2

Bottom Line

Psychosis is not an expected adverse effect of therapeutic-dose ivermectin for approved parasitic infections. When neuropsychiatric symptoms occur, they typically result from: (1) massive overdosing, particularly with veterinary formulations; (2) co-infection with Loa loa in onchocerciasis treatment; or (3) rare idiosyncratic reactions. Healthcare providers should focus on appropriate dosing, screening for Loa loa in at-risk populations, and counseling patients against off-label use or veterinary formulations.