Named bugs, not a general cleanser
Oral Stromectol is a 3 mg human chip written for a parasite with the right channel.
Ivy's desk does not hand out a 'dewormer' the way a feed store hands out paste. The ivermectin monograph is a short list: intestinal Strongyloides, Onchocerca volvulus, and - off the US oral label but in daily clinic - Sarcoptes mites when cream is a poor fit. Each of those organisms carries glutamate-gated chloride channels. Hold the channel open and the parasite's nerve and muscle cells flood with chloride. It stops moving. It stops feeding. That is the whole trick.
You do not have those channels parked on your own nerves the way a worm does. P-glycoprotein at the blood-brain barrier also keeps labeled human levels out of the one place we do have related gates. So a correctly counted 3 mg stack can paralyze a roundworm and barely register in the person swallowing it. That gap is the reason mass programs could give this drug for decades.
A virus has no channel to jam. A strep throat has none either. If someone wants a chip 'just in case,' the answer is a test and a named organism, not a standing bottle. The kilogram arithmetic lives in the Stromectol 3 mg chart. The COVID detour has its own file.
Strongyloides can sit quiet for decades
Soil-acquired Strongyloides can autoinfect one host for years.
People pick this worm up from warm, damp soil, often long before anyone writes a script. The ugly talent is autoinfection: larvae can complete the cycle inside one person, so the infection smolders without a new trip to the beach. Mild gut fuss, a creeping rash, or nothing. Then steroids or chemotherapy drop the immune brake, and the same worm can explode into hyperinfection. That is why we screen and treat before immunity is planned to fall.
The usual human plan is a weight-based oral course near 200 mcg/kg, built from 3 mg chips, then a later stool or serology check. Feeling fine after day one is not clearance. A hidden survivor is exactly the worm that becomes an ICU problem six months later when the prednisone starts.
If the only 'exposure' is a winter cough, Strongyloides is the wrong story. If the story is decades in a tropical childhood plus a new steroid taper, it is the right one. Name the worm. Then count chips.
Onchocerca needs larval shutdown, not one miracle
River-blindness programs count on 150 mcg per kilogram.
Onchocerca volvulus lives in skin nodules and sheds microfilariae that crawl through skin and eyes. The itch and the blindness come from those larvae, not from a single dramatic adult kill. Ivermectin clears the microfilariae and pauses new production for months. Adults keep living. So the public-health rhythm is repeat doses, community after community, until transmission breaks.
That is a different job from a one-day Strongyloides clear. Same 3 mg chip, different mcg/kg target, different calendar. Donation programs ran on this distinction for decades. A traveler who never lived along a blackfly river does not need that calendar. Someone from an endemic belt might.
Ivermectin is not a tonic you take because a Nobel medal hangs on the molecule. Omura and Campbell earned that medal for parasitic disease, not for a respiratory virus. Keep the medal on the worm it was won for.
Mites in skin still need a human tablet
Household scabies plans often pair cream with oral chips.
Sarcoptes burrows in the top of the skin and drives an itch that makes people miserable and contagious. Permethrin cream is still the first reach in a lot of households. Oral ivermectin earns a seat when cream is impractical, when a care home is passing mites down a hallway, or when crusted scabies sits on a weakened host. Same 3 mg human tablet. Same weight math. Not a farm syringe.
Eggs survive the first pass. A second dose about a week or two later catches what hatched. Treat the whole house on the same days or the mites commute. Hot laundry is not folklore. And the itch can last two to four weeks after the mites are dead, because skin is still arguing with leftover debris. New burrows are the failure signal. Old itch is not.
Topical ivermectin for rosacea is a different product on a different shelf. Do not eat the cream. Do not crush a Stromectol chip onto a cheek. If the question is lice or cutaneous larva migrans, that is still a parasite conversation - still not a cough conversation.
Fat, water, and where the chip travels
Classic labeling wants water on an empty stomach.
Stromectol's older US directions still say take the tablets with water, nothing in the gut. That is the clock the labeled milligram target was built around. A fatty meal raises how much of the 3 mg chip you absorb, so a home decision to 'take it with dinner to be nicer' quietly changes the dose. Follow the instruction on the slip you were given, not a forum tip.
Once absorbed, the molecule is fat-loving and stays mostly out of the brain at human levels. Liver CYP3A4 handles most of the breakdown. Most of the dose leaves in feces. None of that ADME picture invents a viral target. It only tells you why food, other CYP3A4 drugs, and a leaky blood-brain barrier in overdose change the safety margin.
If you want the stack numbers rather than the map of bugs, switch to the kilogram chart. If someone is waving a livestock tube because a headline mentioned COVID, read why the trials left the chip on the worm list.
Geography that can turn a good chip dangerous
Central African Loa loa loads can trigger encephalopathy.
In parts of Central and West Africa, Loa loa can pack the blood with microfilariae. Give ivermectin into that load and the sudden die-off can swell tissue and, rarely, inflame the brain. Programs there screen first. This is not a reason to fear a scabies course in Ohio. It is a reason to say if you lived or worked in that belt before anyone counts chips.
The same honesty applies to veterinary paste. A tube built for a 500 kg horse is not a cheaper 3 mg human chip. Fillers were chosen for livestock. The concentration is wrong by design. People guess a ribbon and land in an emergency bay. That is a product error, not a 'stronger brand.'
Ivy will write a human 3 mg script for a named worm or mite. She will not write one for a cough, a 'detox,' or a farm aisle bargain. If your story is travel plus steroids, bring the map. If your story is a winter virus, leave the blister in the drawer.
What this desk will not write a chip for
Coughs, colds, and viral swabs sit outside this molecule.
Ivermectin is a superb antiparasitic and a useless antiviral. That is not a political sentence. It is the channel story plus the trial story. Keep the 3 mg chip on Strongyloides, onchocerciasis, and the mite jobs that earned it. Send the COVID claim to the trial file, and send the stack math to the chart.
The parent label notes sit on the ivermectin page. Dr. Ivy Chukwu answers the mailbag below. None of this is your personal prescription.
Talk with the clinician who knows your weight, your travel, and your other drugs before anyone changes a dose. The legal floor is the desk disclaimer.
Consultation
Reader questions, answered
Answered by Dr. Ivy Chukwu, MD · Infectious disease & internal medicine
Readers who finished the parasite map asked Ivy these.
Nia Okonkwo asksIf I have a cough and I once walked barefoot in a wet climate, does that earn a 3 mg chip?
No. A cough is a respiratory story until someone proves a parasite. Barefoot time in wet soil can matter for Strongyloides, but it earns a test and a history, not a blister because you also have a cold. Ivermectin jams invertebrate chloride channels. A virus has none. If the real worry is a hidden worm before steroids or chemotherapy, say that plainly and we screen. If the real worry is this week's cough, the chip stays in the drawer. The map of who actually earns a script is on this page, and the parent notes sit on the ivermectin monograph. Bring travel years and immune-suppressing plans to the visit. Do not self-start a 3 mg stack on a hunch.
Rafael Mendes asksDad was told he caught Strongyloides as a child. How can a worm wait that long?
Strongyloides can finish its life cycle inside one person. Larvae reinfect the same gut and skin without a new patch of mud. That is why a childhood in a warm, damp place can still be relevant at sixty. Most years it is quiet - a little belly noise, a rash, or nothing. The danger is a later immune drop. Steroids, chemo, or another hit can turn a smolder into hyperinfection, which is an emergency. That is why we treat even when someone feels well, then recheck. Feeling fine after one day of chips is not proof the worm is gone. CDC pages on strongyloidiasis are a clean public summary if you want a second plain-language pass at the CDC.
June Holloway asksWhy do river-blindness programs keep dosing for years if the chip works?
Because the chip clears microfilariae and pauses new larvae. It does not reliably kill the long-lived adults sitting in skin nodules. Adults restart production once the drug wanes, so a single 150 mcg/kg day calms the load and then the clock starts again. Community programs repeat the dose so eyes and skin stay protected and transmission slowly breaks. That is control on the way to elimination, not a one-tablet cure. A person who never lived along a blackfly river does not inherit that calendar. Someone from an endemic belt might. The distinction matters so nobody treats a Nobel medal like a forever vitamin. WHO onchocerciasis pages at WHO sketch the program logic without the forum noise.
Kenji Sato asksWe treated the house for scabies and I still itch. Did the chips fail?
Usually no. Dead mites leave debris, and skin keeps arguing with that debris for two to four weeks. Night antihistamine and a bland moisturizer get most people through it. Failure looks like new burrows, not leftover itch. The second dose a week or two later exists because eggs hatch after the first pass. Treat every close contact on the same days and do the hot laundry, or mites change beds. Oral ivermectin is a human 3 mg tablet counted to weight, not a livestock ribbon. New burrows after both doses are a clinic revisit, not a reason to add farm paste. MedlinePlus scabies notes at MedlinePlus match what we tell households.
Bridget Vaughn asksMy dermatologist gave ivermectin cream for rosacea. Is that the same script?
Same INN, different product, different job. The cream sits on facial skin for rosacea bumps. The 3 mg Stromectol chip is swallowed so a systemic level can reach worms or mites inside you. You cannot swap them. Do not eat the cream. Do not mash a tablet onto a cheek. If the cream is helping the face, keep using it as written. That success says nothing about gut parasites or a cough. Later oral ivermectin for a named worm is a new weight-based plan, not more of the rosacea stuff. FDA labeling for the two forms lives in separate files at the FDA. Ask before you mix shelves.
Omar Farouk asksI worked two years in Cameroon. Does that change a scabies chip?
It can. Loa loa lives in parts of Central and West Africa. A very high blood load plus ivermectin can trigger a severe reaction, including encephalopathy, because larvae die in a crowd. Programs in those belts screen first. A routine scabies course in someone who never left the Midwest does not carry that map. Your work years do. Tell the prescriber before anyone counts 3 mg chips, even if you feel well. Screening is a blood question, not a vibe. This does not make the drug poison. It makes geography part of the history. Bring the country list. The ivermectin page flags the same caution so it is not buried.
Lila Chen asksA coworker takes a chip every month as a cleanse. Should I copy that?
Do not. Ivermectin is not a monthly cleanser or a wellness habit. Without a named parasite it has nothing to bind, so you only buy side-effect risk. The idea that every city household needs a standing 3 mg ritual is not how this desk works. Real risk looks like a specific exposure, a test, a short weight-based course, then a stop. If the monthly supply is livestock paste, the risk is worse, because that concentration was built for a horse. Ask what problem the ritual is solving. If the answer is just in case, stop. If the answer is a real endemic history, go to clinic, not a shared bottle.
General education from a clinician, not personal medical advice. Bring your own history to your own prescriber.