More and more people are asking about ivermectin at the pharmacy counter. Sometimes it is a patient with a recent diagnosis. Sometimes it is a son or daughter who has seen a video and wants to help a parent. It is almost never someone looking for an argument: it is someone frightened who has read that a cheap, well-known medicine exists that the industry would rather they didn't know about.
Answering "that's nonsense" and moving on achieves nothing. The person asking has seen what look like scientific studies — and in a sense they are. So the useful reply is to explain what this drug actually does, how far it gets into the body, and why those studies don't say what they are made to say. All of that can be explained with concrete numbers, and that is what this article is.
The short version. Ivermectin is an excellent antiparasitic with a Nobel Prize behind it, licensed as tablets and as a cream. It does kill tumour cells in a dish — but at concentrations 100 to 1,000 times higher than the human body reaches at the licensed dose. And in at least one well-studied case, that laboratory effect turned out to be an artefact of the experiment itself. No clinical trial shows any benefit in people with cancer.
What ivermectin is, and where it came from
Ivermectin is a semisynthetic derivative of the avermectins, a group of molecules produced by the bacterium Streptomyces avermitilis, isolated from a soil sample in Japan. Its development as an antiparasitic earned William C. Campbell and Satoshi Ōmura the 2015 Nobel Prize in Physiology or Medicine.
That prize is not a decorative detail — it is part of why the claim spreads so well. Ivermectin genuinely is one of the most important medicines of the twentieth century. It all but eliminated onchocerciasis, river blindness, across large parts of Africa and the Americas. It is cheap, given as single doses, and has a very good safety profile in its licensed use. All of that is true, and it is what makes the next leap sound credible. The next leap is not true.
Mechanism of action: why it kills the parasite and not you
Ivermectin binds with high affinity and selectivity to glutamate-gated chloride channels (GluCl), found in the nerve and muscle cells of invertebrates. Binding holds the channel open far longer than glutamate alone would.
Selectivity rests on two things, and both matter
First: we don't have the target. Mammals have no glutamate-gated chloride channels. Our closest equivalent is the GABAA receptor — also a chloride channel, and one ivermectin can act on — but those are confined to the central nervous system.
Second: it doesn't get there. This is the elegant part. P-glycoprotein (P-gp, encoded by MDR1/ABCB1) is an efflux pump at the blood–brain barrier that actively returns ivermectin to the bloodstream, preventing it from accumulating in the brain.
The proof that this is what does the work. Mice with the mdr1a gene knocked out — no pump — are 50 to 100 times more sensitive to ivermectin. It is exactly the same reason collies and related breeds, which often carry a mutation in that gene, can suffer severe neurotoxicity at doses other dogs tolerate perfectly well. Anyone who has worked in veterinary practice knows this one.
Pharmacokinetics: the numbers that settle the argument
This is the section that actually answers the cancer question, so it is worth reading slowly.
- Absorption. Well absorbed orally, with peak plasma levels at around 4 hours.
- Protein binding: 93%. Only about 7% circulates free — and only the free fraction is pharmacologically active.
- Distribution. Highly lipophilic with a large volume of distribution, so it partitions into fat. But it barely enters the CNS, thanks to P-gp.
- Metabolism. Hepatic, mainly via CYP3A4. It is also a P-glycoprotein substrate.
- Half-life. Around 18 hours for the parent drug.
And now the number that changes everything. After a single 12 mg dose in fasting healthy volunteers, measured peak plasma concentrations were 30.6 and 46.6 ng/mL depending on the study. With a molecular weight of about 875 g/mol, that is roughly 0.05 µM. Take away the 93% bound to protein and the free concentration lands near 3.3 ng/mL (0.0035 µM).
Licensed presentations and indications
Ivermectin is not exotic or hard to obtain. In Spain it is marketed and reimbursed, on prescription.
| Route | Presentations | Licensed indications |
|---|---|---|
| Oral | 3 mg and 6 mg tablets. Several generics are marketed in Spain (Ivermectina Teva, Aristo, Stada, Ivercare, Ivergalen, Ivertilene, Zulima). | Intestinal strongyloidiasis · microfilaraemia due to filariasis · human sarcoptic scabies. Also used in onchocerciasis. |
| Topical | Ivermectin 10 mg/g cream (Soolantra). | Inflammatory lesions of papulopustular rosacea in adults. |
The usual oral dose is 200 micrograms per kilogram as a single dose, translated in practice into a tablet count by weight band. In scabies the dose is commonly repeated after 7–14 days to cover the eggs the first dose does not affect.
What you can say with confidence. For what it is licensed for, ivermectin works well and is well tolerated. There is no reason to distrust the drug itself: the scepticism is about what is being attributed to it off-label, which is a different matter entirely.
The cancer claim, point by point
The current wave started in early 2025, when actor Mel Gibson promoted the idea on a very widely heard podcast. The share of cancer-related social media content mentioning ivermectin doubled in the first half of 2025 compared with all of 2024, passing 4% of all cancer-related posts. The same text, translated into several languages, has circulated ever since.
1. The starting premise is false: cancer is not a parasite
Much of the claim rests on the idea that "cancer is really a parasite", and that an antiparasitic would therefore cure it. There is nothing to hold on to here. A tumour is not an invading organism: it is the patient's own cells, which have accumulated mutations and lost control of their proliferation. They have no glutamate-gated chloride channels — no target. The analogy fails at step one, before any study is even discussed.
2. The lab studies exist, and they don't say what they seem to
Here it is worth being honest: there really are papers showing ivermectin killing tumour cells in a dish. Whoever cites them is not making them up. The problem is not that the data are fake — it is that they cannot be transferred to a person, and the reason is arithmetic.
Those experiments work in the micromolar range: typically 1 to 20 µM, that is 875 to 17,500 ng/mL. Compare that with what the body actually reaches:
| Scenario | Concentration | Equivalent |
|---|---|---|
| Peak plasma after 12 mg orally | 30–47 ng/mL | ≈ 0.05 µM |
| Free fraction (the active one) | ≈ 3.3 ng/mL | ≈ 0.0035 µM |
| Concentration used in the in vitro studies | 875–17,500 ng/mL | 1–20 µM |
The distance between the third row and the second is two to three orders of magnitude. That is not a gap you close by raising the dose a little: getting close would mean multiplying exposure by hundreds, far beyond what a human tolerates. It is precisely the argument that dismantled the ivermectin-and-COVID claims, for exactly the same reason.
"It kills cells in a dish" is not a remarkable finding. At high enough concentrations, a great many substances kill cultured cells — alcohol, detergent and salt among them. The relevant question is never whether something kills cells, but at what concentration, and whether that concentration is reachable in a person without killing the person too.
3. And in at least one case, the lab effect was an artefact
This is the most interesting part, and it almost never appears in the videos. A 2022 paper in Toxicology and Applied Pharmacology examined why ivermectin was killing cervical cancer cells in culture, and found something awkward: the ivermectin was precipitating in the medium. It is a strongly hydrophobic molecule, and the "effective" concentrations in use sat right at the limit of its aqueous solubility.
The test was elegant. They filtered the medium to remove particles above 0.2 microns. When they did, the cytolytic effect disappeared in both cell lines. What was killing the cells was not dissolved ivermectin but solid aggregates settling onto them. A residual antiproliferative effect remained with filtered medium — but only above concentrations that are not clinically attainable.
This does not mean every in vitro ivermectin study is an artefact. It does mean that kind of result needs close scrutiny before it leaves the laboratory, and that whoever is sharing those charts online has almost certainly not reached this part of the literature.
4. What actually exists in the clinic
No regulator — not the FDA, the EMA or Spain's AEMPS — has approved ivermectin for any oncology indication, and it appears in no cancer treatment guideline.
That said, the honest answer is not "there is absolutely nothing". Some very early-phase research is exploring ivermectin in combination with immunotherapy. It is worth being clear about what that means: an early-phase trial is precisely the way science says "we don't know". It is not evidence that something works; it is the procedure for finding out whether it is worth looking further. The overwhelming majority of molecules that reach that stage never become treatments.
The difference between "there is a trial running" and "it works" is the difference between buying a ticket and winning the prize. Presenting the first as the second is the heart of the claim.
The real risks of self-medicating
The main harm is not pharmacological
The gravest risk here is not an adverse reaction: it is delaying or abandoning cancer treatment that does have evidence behind it. In many tumours the prognosis turns on weeks. Someone who swaps chemotherapy, surgery or immunotherapy for ivermectin is not "trying something just in case" — they are spending the time that was their best asset.
Veterinary formulations
This pattern was already seen with COVID: unable to get a prescription, some people turn to veterinary ivermectin. These are made for horses or cattle, at far higher concentrations, with excipients never assessed for human consumption and no weight-based dosing reference that applies to a person.
Adverse effects and interactions
- Common in licensed use: asthenia, abdominal pain, nausea, vomiting, diarrhoea, dizziness, drowsiness, pruritus, transient eosinophilia and raised transaminases.
- Mazzotti reaction: in onchocerciasis, up to 27% pruritus, 22% urticarial rash and 22% fever in the first days. This is not drug toxicity — it is the inflammatory response to mass microfilarial death.
- Loa loa: encephalopathy and coma have been reported in patients co-infected with Loa loa at high parasite loads. This is why screening precedes treatment in endemic areas.
- Interactions: as a substrate of CYP3A4 and P-glycoprotein, potent inhibitors of those pathways can raise its exposure — relevant precisely in cancer patients, who usually carry several concomitant treatments.
How to handle this at the counter
This conversation is won with respect and specifics, not disdain. Four things that work:
"You're right that it's an important medicine — it won a Nobel Prize, in fact." Starting by agreeing where they are correct stops the person closing down, and it happens to be true.
"The study you've seen uses hundreds of times more drug than reaches the blood from a tablet. It isn't that nobody tried — it's that you can't get there." It lands without needing a clinical background.
Ask what treatment they are on and whether they are keeping to it. The real goal of the conversation is not winning the ivermectin argument — it is that they don't abandon what is actually helping them.
"Do raise it with your oncologist — and I can write this down for you to take along." They should leave with a plan, not with the feeling they were dismissed.
Frequently asked questions
Does ivermectin cure cancer?
No. There is no clinical trial showing that it shrinks tumours or improves survival in people with cancer, and no regulator — the FDA, the EMA or Spain's AEMPS — has approved it for any oncology indication. The studies circulating on social media are cell-culture experiments, and they use concentrations between one hundred and one thousand times higher than the human body reaches at the licensed dose.
What is ivermectin actually used for?
It is an antiparasitic. Oral ivermectin is licensed for intestinal strongyloidiasis, microfilaraemia due to filariasis and human sarcoptic scabies, and a topical cream is licensed for the inflammatory lesions of rosacea. It is also used in onchocerciasis — river blindness — the disease it was developed for, which earned William Campbell and Satoshi Ōmura the 2015 Nobel Prize in Medicine.
What is ivermectin's mechanism of action?
It binds with high affinity to glutamate-gated chloride channels (GluCl) in the nerve and muscle cells of invertebrates. Opening those channels lets chloride into the cell, hyperpolarises the membrane and paralyses the parasite, which stops feeding and dies. Mammals do not have those channels, and P-glycoprotein at the blood–brain barrier actively pumps ivermectin out of the central nervous system. Its safety rests on both of those facts.
Why don't the in vitro studies prove it works in people?
Concentration. After a single 12 mg oral dose, peak plasma levels are about 30 to 47 ng/mL, and since 93 per cent is protein-bound the free fraction is roughly 3 ng/mL. The laboratory studies showing tumour-cell death work in the micromolar range — of the order of 1,000 to 17,000 ng/mL. On top of that, a 2022 paper showed much of the effect in cervical cancer cells was an artefact: ivermectin was precipitating in the culture medium, and filtering out particles above 0.2 microns abolished the cytolytic effect.
Is it dangerous to take ivermectin on your own?
Yes, in three ways. The most serious is delaying or abandoning cancer treatment that does work. The second is veterinary formulations, made for horses or cattle at concentrations and with excipients never assessed for human use. The third is the drug's own adverse effects and interactions: it is a substrate of CYP3A4 and P-glycoprotein, so drugs inhibiting those pathways can raise its exposure.
Is cancer a parasite?
No. This is the false premise the whole claim rests on. A tumour is not a foreign organism invading the body: it is the patient's own cells, which have accumulated mutations and lost control of their division. They have no glutamate-gated chloride channels — the target ivermectin acts on — so the analogy fails at the very first step.
In one line
Ivermectin is a superb antiparasitic being credited with something its own pharmacokinetics make impossible. It is not that the research hasn't been done: it is that the concentrations at which it does anything in a dish are not reachable in a person. And the price of believing otherwise is not paid by an argument on the internet — it is paid by someone who stops treatment in time to matter.
Sources and where to check
- CIMA — AEMPS — summaries of product characteristics for the Spanish ivermectin presentations: licensed indications, weight-based dosing and adverse reactions.
- EMA — the European Medicines Agency's position on unauthorised uses.
- FDA — approved indications and warnings about off-label use.
- 2015 Nobel Prize in Medicine — Campbell and Ōmura, for the avermectins.
- PubMed — for the 2022 precipitation paper, search "Ivermectin-induced cell death of cervical cancer cells in vitro a consequence of precipitate formation in culture media", Toxicol Appl Pharmacol.
- Cancer Research UK — evidence-based information for patients and families.
Want to check whether ivermectin interacts with the rest of a patient's medication? Cross-check the whole list at once with the drug interactions checker, or look the active ingredient up in the drug reference.