Most Common Side Effects of Ivermectin
The most common side effects of ivermectin are local injection site reactions (pain, redness, swelling) when given parenterally, and systemic effects including dizziness, nausea, diarrhea, headache, and mild gastrointestinal symptoms when given orally. 1
Gastrointestinal Effects
- Nausea, vomiting, diarrhea, and abdominal pain are among the most frequently reported adverse effects after oral ivermectin administration 1
- Dyspepsia and epigastralgia occur in a minority of patients, with one study reporting gastrointestinal side effects in approximately 9% of patients treated for strongyloidiasis 2
- These symptoms are typically mild and transient, resolving without specific intervention 3
Neurological Effects
- Dizziness, headache, and asthenia (weakness) are commonly reported neurological side effects 1
- Disorientation can occur but is less common 2
- These effects are generally mild and self-limited 4
Dermatological Reactions
- Rash, edema, and pruritus are frequently observed cutaneous reactions 1
- Urticaria and contact dermatitis have been reported but are less common 1
- In patients with onchocerciasis, those with hyperreactive onchodermatitis (sowda) may experience more severe reactions including edema and aggravation of skin lesions 1
Other Common Effects
- Fatigue, drowsiness, and irritability are reported systemic effects 1
- Ocular complaints including red eye and conjunctival hemorrhage can occur, particularly in patients with onchocerciasis 1
- Paresthesia (abnormal sensations) has been documented 1
Important Clinical Context
- The FDA label emphasizes that most adverse effects are mild and short in duration 1
- In comparative studies, ivermectin demonstrated significantly fewer adverse events than thiabendazole (31% vs. higher rates with thiabendazole), with better tolerability 5
- One study of ivermectin for strongyloidiasis reported adverse effects in only 2% of patients, all mild and transient 2
- Laboratory abnormalities may occur in approximately 8% of patients but are typically mild and require no specific clinical intervention 3
Critical Safety Considerations
- Post-treatment itching or mild burning of the scalp can persist for days after lice are killed due to inflammatory response to the medication itself, not treatment failure 6
- Rare but serious hepatotoxicity has been reported, with one case showing cytolysis within 2 days of treatment that resolved within 2 weeks 7
- Cardiac dysfunction including sinus tachycardia has been documented, particularly in elderly patients 7
- The elderly population requires particular caution as they may be at higher risk for adverse events 1, 7