What to Know About Ivermectin

Many people with cancer look online for answers. Some websites and social media posts share treatment claims that have not been tested by scientists. These often sound too good to be true, and the information can spread quickly.

The drug ivermectin is one example. It’s gotten a lot of attention in recent years, but is not approved to treat any cancer in people or in animals.

“More and more, my patients are asking about medications like ivermectin. I’m grateful that they’re asking me questions so we can have an informed conversation,” said Merry Jennifer Markham, MD, FASCO, an American Society of Clinical Oncology (ASCO) expert and gynecologic medical oncologist at Moffitt Cancer Center.

What is ivermectin?

Ivermectin is a medication approved to treat and prevent certain infections caused by parasites or worms. It was first developed for use in animals, including dogs, cats, horses, cattle, and other livestock. For example, ivermectin is a common ingredient in heartworm medicine.

All new medicines, treatments, and procedures must go through rigorous testing before they are approved for human use in the U.S. After sufficient human studies, the U.S. Food and Drug Administration (FDA) approved ivermectin for the treatment of certain parasitic infections in humans, including river blindness and threadworms. Ivermectin lotion can also treat skin conditions caused by parasites and other organisms, such as head lice, scabies, and rosacea.

Does ivermectin treat cancer?

Ivermectin is not approved to treat any cancer in people or in animals. No clinical guidelines recommend it as a cancer treatment.

You may have heard unproven claims that ivermectin, and another antiparasitic drug called fenbendazole, can “kill” cancer cells. These claims are based on early studies of ivermectin’s effects on animals and on cancer cells in petri dishes in a laboratory. This limited research has led some people with cancer to find and take ivermectin on their own, without talking to their doctors first.

However, ivermectin has not gone through the rigorous clinical trials needed to ensure it is safe as a cancer treatment in humans. The available research findings are not enough to know if ivermectin could be effective as an anticancer drug in people.

Much more research is needed before ivermectin could potentially be approved to prevent or treat health conditions beyond parasitic infections. It may not be safe or possible for people to take ivermectin at the doses that have been tested and approved for animals. And not enough is known about how cancer cells studied in a laboratory may respond to ivermectin.

“There’s a big gap between what happens under a microscope and what happens in a human being,” Dr. Markham said. “We are many steps away from knowing about the safety or effectiveness of ivermectin in cancer care. Good science takes time because we care about patient safety.”

Stories about the “miracle” of ivermectin frequently leave out important details. They often don’t talk about whether the patient was also taking an approved standard cancer treatment and whether they were taking ivermectin without their doctor’s knowledge. Without data from an actual clinical trial, it’s impossible to know if taking ivermectin affected the person’s cancer outcome.

Risks of taking ivermectin

It’s important to understand the risks and benefits when making any treatment decision. Ivermectin is not approved to treat cancer because it has no proven benefit against cancer. However, it does have many known risks.

 “Ivermectin is safe if taken at the recommended dose to treat a worm infection. That doesn’t mean it’s completely safe in all situations,” Dr. Markham said.

The risks of using ivermectin other than as approved include:

• Large doses of ivermectin can be very dangerous, causing seizures, comas, and even death.
• Ivermectin can have side effects such as nausea, vomiting, and diarrhea. These symptoms may worsen the side effects of standard cancer treatments like chemotherapy.
• Alternative therapies like ivermectin might interact with standard cancer treatments. This could reduce the effectiveness of the standard treatment. It can also raise safety concerns.
• Trying something new without your doctor’s knowledge could harm your health and make it harder for your doctor to provide the care you need.
• Taking ivermectin for a non-approved use could disqualify you from participating in a clinical trial. As a result, your cancer treatment options could be limited.

Can a doctor prescribe ivermectin to treat cancer?

Off-label drug use is common in cancer care. This refers to when a medicine is prescribed or used in a way that is not approved by the FDA, also known as non-approved use or unapproved use.

Doctors may prescribe an approved medicine for an unapproved use if they believe it can help their patient. But they make those decisions based on research-based clinical guidelines and by knowing the risks and benefits to the patient. At this time, no scientific evidence supports prescribing ivermectin off label to people with cancer.

“As an oncologist, I love to jump on new therapies that are proven in scientific studies to have promise for my patients. But you can’t just take a random drug and hope it helps,” said Dr. Markham.

How to make sense of news about cancer treatment

Many people turn to online sources for health information. Cancer is one of the most searched topics. The key to finding good cancer information is to stick to reputable sources and to think critically about what you see, read, or hear.

Here are some questions to ask as you learn about cancer treatments:

• What is the source? Peer-reviewed journals, major news outlets, government agencies, universities, and nonprofit organizations are generally credible sources of medical news and research. If the source is a single person, check their credentials to see if they have scientific expertise or background to make that claim.
• Can you trace the information back to the science? Reliable online sources will list their references, including research studies or guidelines where the information was found.
• Was the research conducted in humans? A treatment that works in a lab or in animals doesn’t always work in people. It may even be harmful. Without rigorous human studies, it is not possible to determine safe doses.
• How strong is the evidence? Consider the size of the cancer clinical trial, how it was conducted, who paid for it, and how many other clinical trials had similar results. Note whether the study included people with your type of cancer and how much it improved their health. Consider the reported side effects.
• Does the information encourage you to stop or avoid standard cancer treatment? Be wary of advice that tells you to go against your doctor’s recommendations. Talk with your doctor before trying anything new.

If you’re curious about an alternative cancer treatment, bring the information to your cancer care team. They can help you figure out what it means for you.

“Understandably, people with cancer want to do whatever they can to regain some control over their health,” Dr. Markham said. “For my patients’ long-term health and safety, it’s really important that I can help them figure out whether information is valid.”

Learn more about health information from the American Cancer Society:

• What to Know About Fenbendazole
• How to Find Cancer Information You Can Trust
• Understanding Information About New Cancer Treatments

Dr. Markham is an ASCO member.