Ivermectin Side Effects: Common Reactions, Serious Warnings & Drug Interactions
Written by Dr. Daniel Foster, Men's Health, Urology & Sexual Wellness Content Specialist
Reviewed for medical accuracy under the Ivermectinkart Editorial Policy
Introduction
Ivermectin is an antiparasitic medicine used in humans for specific infections and, in topical formulations, certain skin or lice conditions. Although it can be well tolerated when appropriately prescribed, ivermectin side effects can range from relatively mild problems such as dizziness, nausea, diarrhea, itching, and rash to rare but serious neurological, liver, or severe skin reactions. Some symptoms after treatment can also result from the body's inflammatory response to dying parasites rather than from direct drug toxicity. Safety depends on the condition being treated, formulation, dose, other medicines, and individual risk factors. Ivermectin can interact with warfarin, and excessive doses or veterinary products can cause dangerous poisoning. This guide explains common reactions, serious warnings, interactions, higher-risk situations, and when to seek medical care.
What Are the Most Common Ivermectin Side Effects?
Commonly reported ivermectin side effects with oral treatment include dizziness, nausea, diarrhea, itching, rash, and other gastrointestinal or nervous-system symptoms. The exact reactions and their frequency depend partly on which parasitic infection is being treated.
In clinical studies included in current U.S. prescribing information, 109 patients receiving ivermectin for strongyloidiasis reported drug-related reactions including dizziness (2.8%), itching (2.8%), diarrhea (1.8%), and nausea (1.8%). Less frequent reactions included fatigue, abdominal pain, loss of appetite, constipation, vomiting, drowsiness, vertigo, tremor, rash, and hives.
These numbers should be interpreted carefully. They come from relatively small clinical studies of particular patients receiving particular treatment regimens, so they should not be treated as universal probabilities for every person who takes ivermectin.
The current U.S. prescribing information for ivermectin tablets separates adverse reactions by the infection being treated because treatment of onchocerciasis can produce additional inflammatory reactions associated with dying parasites.
Ivermectin side effects and how seriously to take them
Possible reaction | What patients should know | General response |
Nausea or diarrhea | Reported with oral ivermectin | Contact your clinician if severe or persistent |
Dizziness or vertigo | Can occur after treatment | Use caution with activities requiring alertness |
Fatigue or drowsiness | Reported in clinical use | Monitor symptoms and seek advice if significant |
Itching or mild rash | Can occur and may sometimes relate to parasite death | Seek advice if persistent or worsening |
Hives | May indicate a hypersensitivity reaction | Contact a healthcare professional promptly |
Low blood pressure | Reported, particularly postural hypotension | Seek assessment for significant dizziness, fainting, or weakness |
Confusion, severe drowsiness, seizure | Potential serious neurological reaction | Seek urgent medical care |
Blistering or peeling skin | Could indicate a severe skin reaction | Seek emergency medical care |
Why Can Ivermectin Reactions Differ Between Infections?
Not every reaction following ivermectin treatment is necessarily caused directly by the medicine. In people treated for onchocerciasis, inflammatory and allergic reactions can occur as microfilariae—the immature form of the parasite—die after treatment.
This is sometimes called a Mazzotti-type reaction.
Possible manifestations can include itching, rash, swelling, fever, joint or muscle symptoms, tender lymph nodes, and changes in blood pressure. Eye-related reactions can also occur with onchocerciasis, although the underlying disease itself can cause some of the same problems.
That distinction matters when interpreting an “ivermectin side effect.” A symptom appearing after treatment may reflect:
A direct adverse effect of ivermectin
An immune response to dying parasites
The infection itself
Another medicine or medical condition
A healthcare professional can consider the type of infection, timing of symptoms, severity, other medicines, and medical history when assessing the likely cause.
“I felt worse after taking ivermectin” does not always mean ivermectin toxicity. With some parasitic infections, treatment can provoke an inflammatory response as parasites die. However, severe neurological symptoms, major allergic reactions, or rapidly worsening illness require prompt medical assessment.
What Are the Serious Warnings and Rare Side Effects of Ivermectin?
Serious reactions to ivermectin are uncommon but can involve the brain and nervous system, liver, blood pressure, or skin. Current U.S. labeling includes post-marketing reports of seizures, hepatitis, severe skin reactions, neurotoxicity, and other potentially serious events.
Post-marketing reports are useful for detecting uncommon safety problems after a medicine reaches wider use. However, these reports generally cannot tell us precisely how frequently an event occurs or prove that ivermectin caused every reported case.
Neurological reactions
Neurotoxicity—harmful effects involving the brain or nervous system—has been reported with ivermectin. Reported manifestations include severe drowsiness or altered consciousness, confusion, disorientation, stupor, coma, and death.
Seizures have also been reported after marketing.
These events have been reported with recommended dosing as well as overdose, meaning severe neurological symptoms should not simply be ignored because someone believes they took an appropriate amount.
Serious skin and liver reactions
Post-marketing reports listed in U.S. labeling include Stevens-Johnson syndrome and toxic epidermal necrolysis. These are rare but potentially life-threatening reactions involving extensive damage to the skin and mucous membranes.
Hepatitis, increased liver enzymes, and increased bilirubin have also been reported.
A severe or spreading rash, blistering or peeling skin, mouth or eye sores, jaundice, or other significant symptoms following treatment require prompt medical attention.
What Drugs Can Interact With Ivermectin?
Warfarin is the drug interaction specifically identified in current U.S. oral ivermectin labeling. Rare post-marketing reports describe an increased international normalized ratio, or INR, when ivermectin was given with warfarin.
INR is a blood test used to monitor the anticoagulant effect of warfarin. A higher-than-intended INR can indicate increased bleeding risk.
The DailyMed ivermectin drug-interaction information specifically documents this post-marketing interaction.
This does not mean everyone taking warfarin will experience an interaction. It does mean patients taking warfarin should make sure the clinician prescribing ivermectin knows about their anticoagulant treatment.
What other medicines should you tell your clinician about?
Provide your healthcare professional with a complete medication list rather than trying to predict which medicines might interact.
Include:
Prescription medicines
Over-the-counter medicines
Vitamins and supplements
Herbal products
Recently discontinued medicines
Online interaction lists sometimes describe many theoretical ivermectin interactions based on how medicines are metabolized. A theoretical pharmacological interaction is not necessarily supported by the same level of clinical evidence as a documented interaction in prescribing information.
Medication-safety dos and don'ts when taking ivermectin
Do | Don't |
Take ivermectin exactly as prescribed for the condition being treated | Increase the dose because symptoms have not improved immediately |
Tell the prescriber if you use warfarin | Assume prescription medicines cannot interact with ivermectin |
Provide a complete medicine and supplement list | Combine medicines based only on an online interaction checker |
Verify that you have a human medicine intended for your condition | Take ivermectin formulated for horses, cattle, or other animals |
Contact a healthcare professional about concerning reactions | Keep taking extra doses after significant adverse effects without seeking advice |
Follow condition-specific follow-up instructions | Use another person's ivermectin prescription |
Who May Need Extra Caution With Ivermectin?
Pregnant or breastfeeding people, young children, older adults with multiple medical conditions, people taking interacting medicines, and people with certain parasite exposures may require additional consideration before oral ivermectin treatment. The specific risk depends on why ivermectin is being considered.
Pregnancy, breastfeeding, and children
Current U.S. labeling states that adequate, well-controlled studies in pregnant women are lacking and that safety in pregnancy has not been established. Ivermectin is also excreted into human milk in low concentrations.
For oral ivermectin tablets, safety and effectiveness have not been established in children weighing less than 15 kg according to the U.S. prescribing information.
These considerations do not substitute for an individual risk-benefit assessment when treatment of a parasitic infection is medically necessary.
Why does Loa loa exposure matter?
A particularly important warning applies to people with substantial exposure to areas of West or Central Africa where Loa loa, another parasitic worm, is endemic.
People with onchocerciasis who also have a heavy Loa loa infection can rarely develop serious or fatal encephalopathy—a disorder affecting the brain—following treatment with an effective microfilaricidal drug. Symptoms reported include confusion, difficulty walking, lethargy, seizures, stupor, and coma.
Current prescribing information therefore recommends pretreatment assessment for loiasis and careful follow-up when clinically appropriate in people with significant exposure to endemic areas.
Can Taking Too Much Ivermectin Be Dangerous?
Yes. Ivermectin overdose can be dangerous, and veterinary ivermectin products should never be used as substitutes for medicines intended for humans. Excessive exposure can cause gastrointestinal symptoms, low blood pressure, problems with balance and coordination, seizures, coma, and potentially death.
The FDA safety information on ivermectin warns that taking large doses can be dangerous and notes that people have required medical care, including hospitalization, after self-medicating with ivermectin products intended for animals.
Veterinary formulations can differ substantially from human medicines. Their concentrations and inactive ingredients are designed and evaluated for animals, not for self-treatment in people.
What about ivermectin for COVID-19?
The FDA has not authorized or approved ivermectin for preventing or treating COVID-19 in humans, and the agency states that available clinical-trial data do not demonstrate that ivermectin is effective against COVID-19 in humans.
Human ivermectin tablets do have legitimate FDA-approved uses: they are approved for intestinal strongyloidiasis and onchocerciasis. Certain topical ivermectin formulations have separate approved uses.
This distinction matters. Safety and effectiveness for an approved parasitic indication do not establish that the same medicine is effective for an unrelated viral illness.
When Should You Seek Medical Help for Ivermectin Side Effects?
Seek urgent medical attention if you develop severe neurological symptoms, difficulty breathing, a serious allergic reaction, extensive blistering or peeling skin, or other rapidly worsening symptoms after taking ivermectin. Significant overdose or accidental ingestion of a veterinary product also requires prompt medical advice.
Warning signs that should not be dismissed include:
Seizure
Confusion or disorientation
Difficulty staying awake or loss of consciousness
Severe difficulty walking or loss of coordination
Fainting or severe low-blood-pressure symptoms
Difficulty breathing
Facial, tongue, or throat swelling
Widespread blistering or peeling skin
Severe rash involving the mouth or eyes
Yellowing of the skin or eyes
If overdose is suspected in the United States, contact Poison Control at 1-800-222-1222 or obtain emergency medical care for severe symptoms. Poison Control advises against making someone vomit after suspected ivermectin ingestion.
Do not try to manage a serious reaction by taking additional medicines or changing ivermectin dosing yourself.
Conclusion
Most ivermectin side effects reported with appropriately prescribed oral treatment are relatively mild, but serious neurological, liver, skin, blood-pressure, and hypersensitivity reactions have also been reported. Some reactions depend on the parasite being treated, while overdose and use of veterinary formulations can create substantially greater risks. Ivermectin can also interact with warfarin.
Take ivermectin only for an appropriate indication and according to professional instructions, and tell your clinician about other medicines and relevant travel or residence history. Seek prompt medical care for severe neurological symptoms, breathing difficulty, major skin reactions, or suspected overdose. This information supports—but does not replace—individual medical advice.
Frequently Asked Questions
1. What are the most common side effects of ivermectin?
Reported effects with oral ivermectin include dizziness, nausea, diarrhea, itching, fatigue, abdominal discomfort, vomiting, drowsiness, rash, and hives. The frequency and type of reactions can vary according to the infection being treated. Some reactions may also result from the body's response to dying parasites.
2. Can ivermectin cause serious neurological side effects?
Yes, rare serious neurological reactions have been reported. U.S. prescribing information includes altered consciousness, confusion, disorientation, seizures, stupor, coma, and death among reported events. Severe drowsiness, confusion, seizures, or major problems with balance or consciousness require urgent medical assessment.
3. Does ivermectin interact with blood thinners?
Ivermectin has a documented potential interaction with warfarin. Rare post-marketing reports describe increased INR when the medicines were taken together, which may affect bleeding risk. Tell the prescriber if you take warfarin so appropriate clinical or INR monitoring can be considered.
4. Is ivermectin hard on the liver?
Liver-related reactions have been reported after ivermectin use, including hepatitis and elevations in liver enzymes and bilirubin, although serious reactions appear uncommon. Seek medical advice for concerning symptoms such as yellow skin or eyes, dark urine, persistent nausea, or significant abdominal symptoms.
5. Is veterinary ivermectin safe for humans?
No. Veterinary ivermectin formulations should not be used as substitutes for human medicines. They can contain different concentrations or ingredients and have not been evaluated for human use in that formulation. The FDA has reported hospitalizations after people self-medicated with ivermectin products intended for animals.
6. Can Ivermectin be used to prevent or treat COVID-19?
Ivermectin is not FDA-authorized or approved for preventing or treating COVID-19. The FDA states that available clinical-trial data do not demonstrate effectiveness against COVID-19 in humans. Ivermectin does have approved human uses for particular parasitic infections, which are separate indications.
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