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Oops! I Just Took My Dog's Heartworm Medicine
Ivermectin Safety

The Bottom Line

Ivermectin is a beneficial and safe antiparasitic drug used for a wide variety of parasitic diseases in humans and animals. Ivermectin is helping to eliminate onchocerciasis (river blindness), a malady that has plagued millions in the world's poorest communities.

The Full Story

Sometimes new drugs are found in unusual places. The antiparasitic drug ivermectin was discovered in the 1970s in bacteria isolated from the soil on a Japanese golf course. Ivermectin was called the first "endectocide" since it was active against both endoparasites (parasites that live inside the host) and ectoparasites (parasites that live on the outside of the host).

Ivermectin was initially developed as a veterinary antiparasitic drug. Of particular importance today is ivermectin's ability to prevent heartworm infections in dogs with monthly dosing (e.g., Heartgard). Ivermectin has also protected hundreds of millions of livestock from a variety of parasites.

Ivermectin lotion is approved by the FDA for the treatment of head lice. Unlike many other treatments for head lice, ivermectin lotion only needs to be applied once. When given orally, ivermectin can be used for treating head or pubic lice and scabies (an itchy, highly contagious skin disease caused by mites burrowing in the skin). Oral ivermectin is useful to control outbreaks of scabies in nursing homes where whole-body application of topical agents is difficult.

Ivermectin's greatest impact on human health has been in Africa. Since 1987, in addition to its use for other parasitic infestations, ivermectin has been used extensively to control onchocerciasis with 1.4 billion treatments so far. Onchocerciasis is also called "river blindness" because the blackfly that transmits the disease breeds in fast-moving streams and rivers. Once within the body, the adult female worm produces thousands of juvenile worms that migrate to the skin and eyes and can produce severe itching and eye injury that can lead to blindness.

Ivermectin kills the juvenile worms, but not the adult females. The effectiveness of the drug lasts up to 12 months, but mature female worms produce offspring for 15 years, so ivermectin has to be taken once a year for that long.

Over 300 million people take ivermectin each year. To date, ivermectin has been shown to be a safe and well-tolerated drug. Most adverse reactions are mild and temporary, such as loss of appetite, headache, muscle aches, lack of energy, and fever. There have been a small number of severe adverse events and even some deaths in humans treated with ivermectin in onchocerciasis-control programs. The reason for these events is unknown, but they might be linked to the presence of large numbers of other parasites that are killed off in treated patients.

If you suspect someone has swallowed ivermectin, do not make the person vomit. Immediately check the webPOISONCONTROL® online tool for help or call Poison Control at 1-800-222-1222.

When ivermectin gets in the eyes, minor irritation and redness can occur. Serious eye injury is not likely, but the eyes should be rinsed immediately. Remove contact lenses and use lots of room temperature water. For children, pour water onto the bridge of the nose and let it gently run into the eyes. Encourage blinking. After rinsing, call Poison Control or use the webPOISONCONTROL tool for help.

Mary Elizabeth May, RN, BA, MPH
Certified Specialist in Poison Information 

For More Information

Onchocercisis (river blindness) 2014

Laing R, Gillan, Devaney E. Ivermectin - old drug, new tricks? Trends Parasitol 2017;33:463-72.


Ivermectin (Sklice) topical lotion for head lice. Med Lett Drugs Ther 2012;54:61-3.

Crump. A. The advent of ivermectin: people, partnerships, and principles. Trends Parasitol 2014:30:423-5

Hall AH, Spoerke DG, Bronstein AC, Kulig KW, Rumack BH. Human ivermectin exposure. J Emerg Med 1985:3:217-9.

Laing R, Gillan, Devaney E. Ivermectin - old drug, new tricks? Trends Parasitol 2017;33:463-72.

Omura S. Ivermectin: 25 years and still going strong. Int J Antimicrob Agents 2008:31:91-8. 


Call 1-800-222-1222 or

HELP ME online

Prevention Tips

  • As with all medications, keep ivermectin products away from children and pets.
  • Ivermectin is not recommended for children under the age of 5 years or weighing less than 15 kg (about 30 pounds).
  • Pregnant or breast-feeding women should not take ivermectin.

This Really Happened

Case 1. A 54-year-old man was brought to an ER along with several empty bottles of ivermectin intended for intravenous (IV) use in horses. He was very drowsy and confused. He had apparently been swallowing the ivermectin for months. His intent was unknown. He also had a leg infection. He was treated with IV antibiotics and fluids. He became agitated and needed to be sedated and evaluated by a psychiatrist. After 4 days in the hospital, he had improved enough to be discharged.

Case 2. An adult cattleman unintentionally injected ivermectin into his hand. He was initially pale and nauseated. He then developed pain and numbness in the affected hand and arm. All of his symptoms resolved without treatment over several hours.

Case 3. A 40-year-old woman mistakenly ingested her dog's heart worm pill containing ivermectin. She called Poison Control and was reassured that she should tolerate this dose. She did not develop any adverse effects. 

Case 4. A 50-year-old woman took her dog's heartworm pill instead of her blood pressure medicine. She immediately recognized the mistake and went online to find out what to do by using the webPOISONCONTROL app. In just three minutes, she entered her age, weight, sex, the name and amount of the drug, and indicated that she had no symptoms. webPOISONCONTROL calculated her dose in mg/kg, determined home treatment was safe, and provided specific instructions to avoid high fat meals, avoid standing rapidly, and watch for listed symptoms suggestive of serious effects. She followed up online two days later, indicating that she remained well.