Ivermectin is not an antibiotic. The FDA-approved human labeling calls it something more specific: the prescribing information for STROMECTOL (ivermectin) tablets, in the September 2024 revision, opens by describing the product as "a semisynthetic, anthelmintic agent for oral administration" — that is, an anti-worm drug. Its chemical family is the avermectins, and the same label's Microbiology section places it in "the avermectin class of broad-spectrum antiparasitic agents." If you want the practical side of that — what it is used for and what the label warns about — that is a separate question from what kind of molecule it is.

It is also not an antiviral or an antifungal in any regulatory sense. As of 28 September 2026, the U.S. Food and Drug Administration lists only two approved indications for the approved oral human products: intestinal (nondisseminated) strongyloidiasis and onchocerciasis, both caused by nematode parasites. The topical products are approved for head lice and for inflammatory lesions of rosacea. Nothing in that set is a bacterial, fungal or viral infection.

Key takeaways

  • FDA-approved labeling classifies ivermectin positively — as a semisynthetic anthelmintic and a member of the avermectin class of antiparasitic agents — rather than by saying what it is not.
  • Its described mechanism is binding to glutamate-gated chloride ion channels in invertebrate nerve and muscle cells. Bacteria, fungi and viruses do not have those channels.
  • The label bounds the spectrum tightly: active against "many but not all nematodes," against Onchocerca volvulus microfilariae but not adults, and against Strongyloides stercoralis only in its intestinal stages.
  • The 2015 Nobel Prize in Physiology or Medicine recognized Campbell and Ōmura, in the citation's words, "for their discoveries concerning a novel therapy against infections caused by roundworm parasites."
  • Animal ivermectin products are labeled for animal use only and are not approved for people.

The direct answers: not an antibiotic, not an antiviral, not an antifungal

A researcher collecting a soil sample in a small glass jar at the grassy edge of a golf course, the kind of sampling that led to the discovery of avermectin.

An honest answer has to note how the sources are written. As of 28 September 2026, no FDA-approved ivermectin label reviewed for this article contains a sentence stating that ivermectin is not an antibiotic, or not an antifungal. The labels answer the question the other way round, by assigning a class.

Class term Where it appears
"a semisynthetic, anthelmintic agent for oral administration" STROMECTOL tablets, DESCRIPTION (label revised 09/2024)
"a member of the avermectin class of broad-spectrum antiparasitic agents" STROMECTOL tablets, CLINICAL PHARMACOLOGY — Microbiology
"the avermectin family of macrocyclic lactones" SOOLANTRA (ivermectin) cream, 1%, section 11 (DailyMed page updated 24 October 2024)
"the macrocyclic lactone class of endectocides" FDA-approved ivermectin injection for cattle and swine, ANADA 200-447 — labeled for animal use only, not approved for people
"the antiparasitic drug ivermectin" Letter to stakeholders from the director of FDA's Center for Veterinary Medicine, 10 April 2020

On the antiviral question specifically, FDA once said it in words: the sentence "Ivermectin is not an anti-viral (a drug for treating viruses)." appeared on an FDA consumer page whose content was current as of 5 March 2021. That sentence was gone from the 10 December 2021 edition and is not on the current page, so it should not be quoted as today's FDA language. What FDA does say now, on a page whose content is current as of 5 April 2024, is that it "has not authorized or approved ivermectin for use in preventing or treating COVID-19 in humans or animals," and that currently available clinical trial data do not demonstrate effectiveness for that use. A warning letter dated 16 March 2023 quoted a seller's antiviral framing and restated that approved ivermectin tablets are for strongyloidiasis and onchocerciasis and are available by prescription only.

What an avermectin is, and where the molecule came from

A veterinary technician loading a slide onto a microscope in a barn-side clinic office, where parasite species and drug class determine what a treatment can reach.

The STROMECTOL label states that ivermectin "is derived from the avermectins, a class of highly active broad-spectrum, anti-parasitic agents isolated from the fermentation products of Streptomyces avermitilis." So the starting material is a soil bacterium's fermentation product — which is why the word "antibiotic" hovers around ivermectin in casual writing. Origin is not class: many drug families come from soil microbes without being antibacterial.

"Avermectin" is the chemical family; "macrocyclic lactone" describes the ring structure. Notably, the word macrocyclic does not appear on the STROMECTOL label at all — it appears on the SOOLANTRA cream label and on FDA-approved animal labeling. In veterinary practice the same grouping is used: the American Association of Equine Practitioners' 2024 Internal Parasite Control Guidelines list "Macrocyclic lactones (ivermectin, moxidectin)" as one of the anthelmintic drug classes marketed in the U.S.

Ivermectin is semisynthetic because a natural product was altered in the laboratory. The Nobel Assembly's 5 October 2015 press release puts it in one sentence: the purified agent was named Avermectin, "which was subsequently chemically modified to a more effective compound called Ivermectin."

The mechanism: glutamate-gated chloride channels in invertebrates

People waiting in a shaded queue at an outdoor community medicine distribution point of the kind used in river blindness programs.

The STROMECTOL Microbiology section describes the class action directly: compounds of the class "bind selectively and with high affinity to glutamate-gated chloride ion channels which occur in invertebrate nerve and muscle cells," which increases chloride permeability, hyperpolarizes the nerve or muscle cell, and results in paralysis and death of the parasite. The label adds a hedge that is worth keeping: compounds of this class "may also interact with other ligand-gated chloride channels, such as those gated by the neurotransmitter gamma-aminobutyric acid (GABA)." That is a possibility statement, not an established second mechanism.

The AAEP's 2024 guidelines describe the same target in nematode nerve and muscle cells and call the result "flaccid paralysis," adding that macrocyclic lactones also kill arthropod parasites. Attribute that phrasing to AAEP; the FDA label says only paralysis and death.

One caution about mechanism talk: the SOOLANTRA cream label states plainly that "the mechanism of action of SOOLANTRA cream in treating rosacea lesions is unknown." The common explanation involving mites and inflammation is not on the label.

Why mammals are largely spared, and what the blood-brain barrier has to do with it

A farmer checking plain unbranded animal medicine bottles on a barn shelf, a reminder that animal ivermectin products are labeled for animal use only.

The human label gives its own explanation of selectivity: it attributes the class's selective activity to the facts that "some mammals do not have glutamate-gated chloride channels" and that the avermectins have low affinity for mammalian ligand-gated chloride channels, adding that ivermectin "does not readily cross the blood-brain barrier" in humans.

The FDA-approved animal injection label (ANADA 200-447) states the same idea more flatly — that mammals do not have glutamate-gated chloride channels — without the human label's "some," and attributes the margin of safety additionally to poor blood-brain barrier penetration. Both labels were read side by side on 28 September 2026; the wording difference is real and worth knowing if you see the sentence quoted without a source.

Two limits on this reassurance. First, none of the five FDA-approved ivermectin labels reviewed attributes the blood-brain barrier exclusion to P-glycoprotein, a mechanism frequently asserted elsewhere. Second, "largely spared" is not "never affected": the STROMECTOL WARNINGS section reports neurotoxicity with ivermectin use, including alteration of consciousness of variable severity, confusion, disorientation and death, in patients without onchocerciasis as well as in patients with onchocerciasis and no Loa loa co-infection.

What the mechanism predicts about which organisms it can affect

An invertebrate ion-channel target predicts activity against some worms and arthropods and predicts nothing at all about bacteria, fungi or viruses. The approved labeling is narrower still than "antiparasitic" suggests.

Organism or condition What FDA-approved U.S. labeling says
Strongyloides stercoralis STROMECTOL is indicated for intestinal (nondisseminated) strongyloidiasis; the label states its activity "is limited to the intestinal stages." Recommended dose: a single oral dose of about 200 mcg/kg.
Onchocerca volvulus Indicated for onchocerciasis; active against tissue microfilariae "but not against the adult form," with an explicit label NOTE that the drug has no activity against adult parasites. Recommended dose: a single oral dose of about 150 mcg/kg.
Other nematodes The label states ivermectin is active against various life-cycle stages of "many but not all nematodes."
Head lice The OTC Drug Facts panel for SKLICE (ivermectin) lotion lists Ivermectin 0.5%, Purpose "Lice treatment," Use "treats head lice."
Rosacea SOOLANTRA cream 1% is indicated for inflammatory lesions of rosacea; the label says the mechanism is unknown.
Scabies No FDA-approved human ivermectin product in the United States carries an approved scabies indication.
Bacteria, fungi, viruses No approved indication. FDA states it has not authorized or approved ivermectin for preventing or treating COVID-19 in humans or animals (page content current as of 5 April 2024).
Horse gastrointestinal parasites AAEP's 2024 guidelines list macrocyclic lactone label claims for cyathostomins, large strongyles, ascarids, pinworms, threadworms and bots. These are animal products, labeled for animal use only and not approved for people. For ascarids, AAEP states macrocyclic lactone resistance "should be assumed until documented otherwise."

Generic name, chemical identity and how it appears in drug databases

The generic name is ivermectin. In the United States the brand names attached to approved human products are STROMECTOL tablets (NDA 050742, originally approved 22 November 1996 as a Type 1 New Molecular Entity), SOOLANTRA cream 1% (NDA 206255, approved 19 December 2014) and SKLICE lotion 0.5% (NDA 202736, approved 7 February 2012).

Chemically, the label defines ivermectin as a mixture containing at least 90% of one dihydroavermectin component and less than 10% of a second, generally referred to as H2B1a and H2B1b. Their empirical formulas are C48H74O14 and C47H72O14, with molecular weights of 875.10 and 861.07. It is "a white to yellowish-white, nonhygroscopic, crystalline powder with a melting point of about 155°C," insoluble in water but freely soluble in methanol. The SOOLANTRA label uses a different specification for the same active ingredient — not less than 95.0% and not more than 102.0% of the combined components — a reminder that "ivermectin" denotes a defined mixture, not a single molecule.

What the databases show, and one trap

Counted from the FDA Orange Book product file dated 11 September 2026 (the online Orange Book search states it is current through September 2026), there are 15 distinct FDA applications for human ivermectin products across 17 product rows, in three dosage forms only: oral tablet, topical cream and topical lotion. Oral tablet strengths listed are 3 mg and 6 mg. Every approved human product is prescription-only except the 0.5% topical lotion for head lice, which is over-the-counter — and which reached OTC status through a prescription-to-OTC switch approved 27 October 2020, not through an OTC monograph. The trap: an openFDA Drugs@FDA query filtered on generic name returned only 13 applications on 28 September 2026, missing ANDA 216808 and ANDA 212485. Database counts depend on which field you search.

Animal formulations sit in a different part of federal regulation entirely: ivermectin injectable solution for animals is codified at 21 CFR 522.1192, which specifies solution strengths of 10 mg and 2.7 mg of ivermectin per mL along with sponsors, species and conditions of use. Those products are labeled for animal use only and are not approved for people.

Discovery: the soil sample, Merck and the Kitasato Institute

Satoshi Ōmura, born in 1935 in the Yamanashi Prefecture, Japan, was a researcher at the Kitasato Institute from 1965 to 1971 and Professor at Kitasato University from 1975 to 2007. He isolated new Streptomyces strains from soil samples and, per the Nobel press release, "from many thousand different cultures, he selected about 50 of the most promising." The Nobel Committee's Scientific Background identifies the productive one as a strain "found in soil nearby a golf course in Ito, Japan," later also called Streptomyces avermectinius.

William C. Campbell, born in 1930 in Ramelton, Ireland, was with the Merck Institute for Therapeutic Research from 1957 to 1990. The press release credits him with showing that a component from one of the cultures was remarkably efficient against parasites in domestic and farm animals; the agent was purified, named Avermectin, chemically modified into ivermectin, and "later tested in humans." Collectively, the Nobel Assembly wrote, the two contributions "led to the discovery of a new class of drugs" — a class, note, not an addition to an existing one.

The Mectizan Donation Program and river blindness

Onchocerciasis, or river blindness, is one of the two approved oral indications, and the label's own limits explain why it is treated repeatedly rather than once: the drug acts on microfilariae and, by the label's explicit NOTE, has no activity against adult O. volvulus.

The Nobel Committee's Scientific Background credits Merck's then-CEO Roy Vagelos with influencing the company to make needed quantities of ivermectin freely available to governments and patients for river blindness and lymphatic filariasis. A 2015 review in PLOS Neglected Tropical Diseases, written by Mectizan Donation Program staff, dates the program's establishment to 1987. This article deliberately does not quote cumulative treatment totals or anniversary figures: those come from company and program communications rather than from primary regulatory records, and they were not independently verifiable for this piece. The donation program also operates outside the U.S. label — in the United States the approved indications remain the two nematode infections.

The 2015 Nobel Prize citation, in its own words

The Nobel Assembly at Karolinska Institutet, which consists of 50 professors and whose Nobel Committee evaluates nominations, announced the award on 5 October 2015. The official citation states that the prize was divided, one half jointly to William C. Campbell and Satoshi Ōmura "for their discoveries concerning a novel therapy against infections caused by roundworm parasites" and the other half to Tu Youyou for her discoveries concerning a novel therapy against Malaria. The prize shares were one quarter each to Campbell and Ōmura and one half to Tu Youyou.

The operative phrase is "roundworm parasites." The prize was not awarded for antibacterial, antifungal or antiviral work, and the citation is the shortest available answer to the classification question.

Why classification matters when you read a label

Class tells you the kind of target; it does not tell you the approved use, the dose or the safety profile. On the STROMECTOL label those are all specific and all differ by indication: about 200 mcg/kg as a single oral dose for strongyloidiasis versus about 150 mcg/kg for onchocerciasis, with two separate weight-band tables that are not interchangeable. Tablets are directed to be taken "on an empty stomach with water"; a 30 mg dose after a high-fat meal produced roughly a 2.5-fold increase in bioavailability compared with fasting. The plasma half-life in humans is approximately 18 hours — which is a half-life, not a duration of effect and not a withdrawal interval — and ivermectin and its metabolites are excreted almost exclusively in the feces over an estimated 12 days. Metabolism is primarily by CYP3A4. The label's entire Drug Interactions section is one sentence about rarely reported increased INR with warfarin; its only contraindication is hypersensitivity to any component; it states ivermectin should not be used during pregnancy since safety in pregnancy has not been established; and safety and effectiveness in patients weighing less than 15 kg have not been established.

Classification also will not settle legal access. The FDA-approved human oral products are prescription-only nationwide, and the only over-the-counter approved product is the 0.5% lotion for head lice. Separately, as of the state-law record maintained for this site, seven states have enacted an ivermectin access law — a law that lets a pharmacy supply human ivermectin without a patient-specific prescription: Arkansas (SB 189 / Act 396, Ark. Code Ann. § 20-7-147; effective date not established in our record; nobody at the counter), Idaho (S 1211, Idaho Code § 37-135, in force 14 April 2025; nobody at the counter), Iowa (HF 2676, Iowa Code § 126.24, in force 1 July 2026, pharmacy gatekeeper), Louisiana (SB 19 / Act 464, La. R.S. 37:1218.3, in force 20 June 2025, pharmacist standing order), Missouri (§ 338.208 RSMo, pharmacist protocol), Tennessee (Public Chapter 908 of 2022, collaborative pharmacy practice agreement) and Texas (HB 25, in force 4 December 2025, pharmacist protocol). Five of those seven route the decision through a pharmacist or a pharmacy; only Arkansas and Idaho put nobody at the counter. North Dakota (HB 1514, N.D.C.C. § 43-15-42.4, in force 15 November 2021) is routinely counted as an eighth, but it is not an access law: it is a shield law, protecting the prescriber or pharmacist from discipline or liability, and it creates no new route for a patient — a prescription is still required there. No other state should be described as having an access law, and news roundups are not a reliable source for this.

Finally, the class name on an animal product is the same, but the product is not. FDA-approved ivermectin products for cattle, swine, horses and other species are labeled for animal use only and are not approved for people; FDA's Center for Veterinary Medicine wrote to stakeholders on 10 April 2020 specifically to say animal ivermectin should not be used as a COVID-19 treatment in humans. If you are comparing a carton in your hand against what you have read, the approved-use and side-effect summary and the tablet product details are the places to check the specifics.

Frequently asked questions

Is ivermectin an antibiotic?

No. FDA-approved labeling classifies it as a semisynthetic anthelmintic and a member of the avermectin class of broad-spectrum antiparasitic agents. It is derived from fermentation products of a soil bacterium, Streptomyces avermitilis, which is probably the source of the confusion — but origin and drug class are different things. As of 28 September 2026, the labels make the positive classification rather than stating the negative.

Is ivermectin an antiviral?

It has no FDA-approved antiviral indication. FDA published the sentence "Ivermectin is not an anti-viral (a drug for treating viruses)." on a consumer page whose content was current as of 5 March 2021; that sentence has since been removed. FDA's current position, on a page whose content is current as of 5 April 2024, is that ivermectin is not authorized or approved for preventing or treating COVID-19 in humans or animals and that available clinical trial data do not demonstrate effectiveness for that use. A proposed nuclear-transport mechanism often cited for laboratory antiviral activity appears in none of the FDA-approved labels reviewed here.

Does ivermectin cross the blood-brain barrier?

The STROMECTOL label states that ivermectin "does not readily cross the blood-brain barrier" in humans, and cites this along with low affinity for mammalian ligand-gated chloride channels as part of why the class is selective for parasites. "Not readily" is not "never," and the same label's WARNINGS section reports neurotoxicity, including altered consciousness, confusion, disorientation and death.

What is ivermectin's generic name, and what are the brands?

Ivermectin is itself the generic name. In the U.S., approved brand-name human products are STROMECTOL tablets, SOOLANTRA cream 1% and SKLICE lotion 0.5%; generic tablets, creams and lotions are approved under separate ANDAs. One labeling quirk to know: the SOOLANTRA header reads "Initial U.S. Approval: 1996," which refers to the first U.S. approval of the ivermectin molecule, not to the cream, which was approved 19 December 2014.

Did ivermectin win a Nobel Prize?

The 2015 Nobel Prize in Physiology or Medicine was awarded, in part, for the discoveries behind it. One half went jointly to William C. Campbell and Satoshi Ōmura for discoveries concerning a novel therapy against infections caused by roundworm parasites; the other half went to Tu Youyou for work on malaria. Prizes go to people and discoveries, not to products.

Is any ivermectin product available without a prescription?

At the federal level, yes, but only one kind: the 0.5% topical lotion for head lice is over-the-counter, having switched from prescription status on 27 October 2020. All approved oral tablets and topical creams are prescription-only. Seven states have separately enacted access laws, listed above; those laws change what a pharmacy or pharmacist may do in that state and do not change the federal approval status. North Dakota is often counted as an eighth, but its statute only shields prescribers and pharmacists from discipline or liability — it opens no new route, and a prescription is still required there.

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