While ivermectin is mostly safe and well-tolerated, it is important to know about possible side effects. This guide covers everything from mild reactions to serious signs that need quick medical help.
Most Common (more than 1%):
- Dizziness, headaches
- Nausea, diarrhea
- Tiredness, weakness
- Skin rashes or itchiness
Serious (rare):
- Severe skin reactions
- Changes in vision
- Seizures or confusion
- Trouble breathing
For proper doses, see our link on dosing information.
Dizziness and lightheadedness, which are common:
- Affect up to 10% of those treated
- Usually mild and go away quickly
- Happen more in older adults
Tips to help manage:
- Rise slowly from sitting or lying down
- Don’t drive if dizzy
- Drink plenty of water
- Usually, the dizziness stops within 1-2 days
Headaches:
- Mild or moderate in most cases
- Can be eased with acetaminophen
- See your doctor if severe or does not go away
Nausea and vomiting:
- Common, but mild
- Drinking small sips of water might help
- Use anti-nausea meds if needed
Diarrhea:
- Usually short and mild
- Drink enough fluids
- Tell your doctor if it is very bad or bloody
Stomach pain:
- Mild cramping is common
- May be from parasite die-off
- Should get better in a few days
Loss of appetite:
- Temporary drop in hunger
- Normal eating usually resumes soon
- Keep hydrated
Skin rashes and itchiness:
- May be mild reactions or part of parasite die-off
- Usually, they go away on their own
- Antihistamines can help with relief
When to worry:
- Severe rashes or blisters
- Rash spreads fast
- Comes with fever or face swelling
Feeling very tired or weak:
- Often after treatment
- Rest and let the body heal
- Should get better in about a week
Muscle or joint aches:
- Mild pain is common
- Over-the-counter pain meds help
- More likely with treatments for river blindness
When treating river blindness, side effects often come from parasites dying, not directly from the drug.
Symptoms of this include:
- Fever, chills
- Itching that is strong
- Swollen, sore lymph nodes
- Muscle and joint pain
- Fast heartbeat
- Eye swelling or irritation
- Face swelling
- Feeling weak
This often starts within 1-2 days after treatment and peaks at 2-3 days. It then improves over 1-2 weeks. You can take antihistamines for itching, acetaminophen for fever and pain, and corticosteroids for severe reactions. Usually, reactions are worse at first and get milder with later doses. This is normal and shows the parasites are dying. But if reactions are very bad, tell your doctor.
Watch out for serious reactions like Stevens-Johnson Syndrome or Toxic Epidermal Necrolysis. Signs include a wide rash with blisters, skin peeling, sores in the mouth or eyes, and flu-like symptoms. Seek emergency care immediately. This can be life-threatening.
Seizures or convulsions may happen if doses are too high or if one has a history of seizures. Risk factors include medications that affect the brain. Severe confusion or mental changes—such as disorientation, hallucinations, or being very sleepy or unresponsive—are serious. Loss of consciousness, fainting, or inability to wake also need urgent care.
Eye problems: sudden vision changes, severe pain, sensitivity with pain, or blurred vision that does not get better. Mild irritation can happen, but sudden serious changes need quick help.
Fast or very slow heart rate: over 120 bpm at rest, chest pain, or trouble breathing are serious. Feelings of faintness, cold sweat, or low blood pressure can also be dangerous.
Trouble with breathing, such as shortness of breath, wheezing, or chest tightness, requires urgent help. Call 911 if you have breathing trouble.
People living in parts of Africa may face more risks. Endemic areas include central and west Africa. Before treatment, screening for worms like Loa loa is needed. If positive, other options are better. Close follow-up is important, as some people can develop severe brain issues, like confusion, inability to walk, coma, or death. To lower risk, monitor liver health, as the drug is processed in the liver. People with liver disease may get more side effects and may need dose adjustments. Watch for signs of toxicity.
People with strongyloidiasis (another parasite) may risk hyperinfection if they get ivermectin. They might need more than one dose and careful monitoring. Longer follow-up is advised to catch any failure of treatment.
Certain drugs can raise ivermectin levels. These include some antifungals like ketoconazole and itraconazole, certain antibiotics like erythromycin and clarithromycin, and some HIV meds like ritonavir. Other drugs called P-glycoprotein inhibitors, such as cyclosporine and verapamil, can also increase levels, raising side effect risk.
In all, knowing these signs and risks helps keep treatment safe. Always follow your healthcare provider’s guidance.
Risk: Greater CNS (brain and nerve) side effects
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Warfarin (a blood thinner):
- Ivermectin may make bleeding more likely
- Watch INR levels closely
- You might need to lower your dose
Digoxin (a heart drug):
- Ivermectin may raise digoxin levels
- Look for signs of digoxin poisoning
- Check digoxin blood levels
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Central Nervous System (brain and nerves) depressants:
- Benzodiazepines like alprazolam and diazepam
- Opioids (pain medicines)
- Sedating antihistamines (allergy medicines)
- Alcohol
Effect: More dizziness, sleepiness, confusion
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- All drugs and supplements
- Any health problems
- Allergies
- Recent travel history
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- Loa loa if you live in areas with it
- Liver health if you have liver disease
- Pregnancy test if needed
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- Take on an empty stomach
- Drink a full glass of water
- Take exactly as your doctor says
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- Do not drive if you feel dizzy
- No alcohol
- Rest if needed
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- Drink plenty of fluids
- Helps work better and cut side effects
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- Keep a journal of any side effects
- Write down how bad they are and how long they last
- Tell your doctor about problems
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- Go to all check-ups
- Finish follow-up tests
- Tell your doctor if symptoms last or get worse
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Call your doctor if you get:
- Side effects that last more than a week
- Severe diarrhea or vomiting
- Symptoms get worse even though you are being treated
- New or strange symptoms
- A rash that spreads or gets worse
Seek urgent help (call 911) if you have:
- Trouble breathing
- A severe allergic reaction (anaphylaxis)
- Seizures or pass out
- Chest pain
- Severe confusion or can't wake up
- Signs of Stevens-Johnson Syndrome
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FDA MedWatch:
- Report serious side effects
- Help make drugs safer
- Call 1-800-FDA-1088 or visit www.fda.gov/medwatch
Why report:
- Add to safety data
- Help other patients
- Especially for rare problems
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Yes. Side effects usually depend on dose. Larger doses tend to cause more and worse side effects. That is why taking the right dose is very important.
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Most side effects go away within 2 to 5 days. The Mazzotti reaction from onchocerciasis treatment may last 1 to 2 weeks but will slowly get better.
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Acetaminophen (Tylenol) is usually safe for pain and fever. Avoid NSAIDs like ibuprofen at first, as they may hide serious signs. Always check with your doctor.
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For approved uses like yearly treatment of onchocerciasis, ivermectin has been used safely for many years. But regular checks are needed.
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Side effects are parts of how the drug works. Allergic reactions happen when the immune system reacts. They may cause hives, swelling, trouble breathing, or be life-threatening.
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Learn what conditions ivermectin treats and how to take it. Correct dosing lowers the chance of side effects. Read full info on ivermectin.
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- FDA. (2024). Stromectol (Ivermectin) Side Effects. US Food and Drug Admin.
- Merck. (2026). Stromectol Prescribing Info: Warnings and Care.
- Drugs.com. (2026). Ivermectin Side Effects in Detail.
- Medscape. (2026). Ivermectin Toxicity and Reactions.
- WHO. (2026). Safety Checks for Ivermectin in Mass Treatment.
Last update: January 17, 2026 Author: Dr. Sarah Chen, MD - Infectious Disease Doctor Reviewed: Medical team
