Start with the organism, then count tablets
Clinics do not open Stromectol because someone forwarded a thread. They open it when a stool, a skin scrap, a serology, or a travel history names an invertebrate the 3 mg tablet is built to hit.
That is the triage. Name first. Dose second. The human product is one strength - 3 mg - so the milligram total is a tablet count from body weight, not a menu of 6 mg or 12 mg pills. Those strengths are folklore. The label never printed them.
Two US-labeled organisms sit at the top of the map: Strongyloides stercoralis in the gut, and Onchocerca volvulus in skin and eye. Different mcg-per-kilogram anchors. Different follow-up. Same tablet. If the consult cannot point at one of those - or at a mite plan a clinician is willing to own - the drawer stays shut.
Readers often want a third lane: 'I feel off, I read it helps.' Feeling off is not an organism. A viral season is not an organism. A tube meant for a 500 kg horse is not a human dosing tool. The map is short on purpose. Short maps are easier to defend at the desk.
Intestinal Strongyloides is the US tablet's main ticket
Soil-acquired Strongyloides stercoralis can sit quiet for years. That is why a US clinic sees this worm more often than river blindness, even though both names are on the label.
The labeled job is intestinal - nondisseminated - strongyloidiasis. One oral dose aimed at about 200 mcg per kilogram, empty stomach, water. A 70 kg adult is not a 50 kg adult. The 3 mg chips add up. After the dose, stool checks still matter. The tablet is not a certificate of clearance.
The worm's trick is autoinfection. Larvae can complete a loop inside one person, so a beach holiday from a decade ago still counts. Mild gut complaints, a creeping rash, or nothing at all. The danger is not the quiet years. The danger is the moment steroids, chemotherapy, or another immune hit turns a smolder into hyperinfection - larvae in lungs, gut, bloodstream. That is a ward problem, not a wellness problem.
So the script is often earned before the immune hit, not after the crash. Screen people with the right travel or birth-country story. Treat a confirmed or high-probability load. Recheck. Do not call a single 3 mg chip a lifetime vaccine. And do not skip the conversation because the person 'feels fine.' Fine is how this worm prefers to travel.
Disseminated disease is a different intensity. The outpatient 200 mcg/kg line is written for the intestinal form. Complicated hosts need a specialist plan, sometimes repeated doses, always follow-up. That still lives on the parasite map. It is not a reason to hand the same strip to a coworker with a cough.
River blindness still owns the public-health lane
Onchocerca volvulus earned the donation campaigns and the Nobel, not a pandemic subplot. In a US exam room it is less common. On the map it still owns its own row.
Blackflies along certain rivers deliver the worm. Adults live in skin nodules. Microfilariae wander through skin and eye. Itch, skin damage, and blindness are the bill. The tablet's labeled aim is about 150 mcg per kilogram - not the 200 used for Strongyloides. Same 3 mg chips. Different arithmetic. Empty stomach again.
One swallow does not kill the long-lived adults. It knocks down the larvae and quiets adult output for months. Mass programs often return yearly. An individual patient may be retreated as soon as three months if the clinician is chasing a load, not running a village campaign. That is control, then elimination pressure - not a one-pill cure story.
If the person has never been in an endemic belt, this row is usually closed. If they have, the question is not 'should everyone take ivermectin in spring.' The question is whether skin, eye, and exposure line up, and whether Loa loa risk (below) has been thought through. Public-health success is not a license to reuse the brand for whatever is trending.
Scabies lives in a gray clinic drawer
Permethrin cream still leads most ordinary mite cases. Oral ivermectin enters when cream is impractical, crusted disease is on the table, or a whole house or ward has to be treated on the same night.
In the United States that oral use is a clinic call, not the Stromectol indication sentence. The usual borrowed plan is still weight-based - about 200 mcg/kg - and a second swallow a week or two later, because eggs hatch after the first pass. Treat close contacts together. Hot laundry is part of the prescription, not a lifestyle tip.
Itch that lingers two to four weeks after mites die is common. Dead-mite debris, not a live city. Moisturizer and an antihistamine buy time. New burrows are the retreat signal. People confuse those two and ask for a third bottle of paste they bought for a horse. Wrong product. Wrong species. Wrong dose.
Crusted (Norwegian) scabies is a different density of mites and a different intensity of plan - often more than one oral dose plus topical, plus infection-control. Immunosuppressed hosts land here. That still earns a human tablet counted from kilograms. It does not earn a livestock syringe.
Head lice and cutaneous larva migrans show up in the same gray drawer in some desks. Rosacea cream and lice lotion are other ivermectin products with other labels - surface jobs, not the systemic 3 mg map. Swallowing cream or rubbing tablets on a face is not clever compounding. It is a category error. Ask Dr. Noor Haddad if the product in the bag does not match the organism on the note.
Viruses, bacteria, and livestock paste never earn the chip
Dish experiments that looked antiviral needed concentrations a human tablet cannot safely reach. Large COVID trials did not turn that hint into a clinical win. The map stops there.
A virion has no glutamate-gated chloride channel to jam. A streptococcus does not either. So colds, flu, COVID, sinus pain, and 'immune support' are not near-misses. They are the wrong kingdom. Stocking Stromectol for the next respiratory season is leftover-pandemic habit, not prophylaxis.
Veterinary paste exists because a horse weighs hundreds of kilograms and the paste is concentrated for that body. Eyeballing a strip of livestock product is how people land in emergency bays with tremor, confusion, or worse. The human 3 mg tablet looks modest because the human target dose is in micrograms per kilogram. Modest is the point. Guessing up from a barn tube is the opposite of modest.
Wellness accounts like to blur 'used in billions of doses' with 'safe for whatever I want.' Billions of supervised doses were for parasites on a program schedule. That safety record does not transfer to a virus, a bacterial UTI, or a monthly 'cleanse.' No organism, no benefit - only exposure. If a friend is already swallowing paste, the next step is a clinician and a human product conversation, not a second tube.
Weight math and the Loa loa hold
Human tablets come only as 3 mg. The labeled Strongyloides line is about 200 mcg/kg. The onchocerciasis line is about 150 mcg/kg. Those two numbers are why a scale belongs in the consult, not a 'one tablet for everyone' story.
A 60 kg adult and a 90 kg adult do not share a chip count. Children do not share an adult count. The label prints weight bands for a reason. Empty stomach, water - that is the administration line, not folklore. Food is not the star of this brief. Weight is.
The safety record that people quote is real for labeled hosts at labeled doses. The loud exception is Loa loa in parts of Central Africa. A very high blood microfilarial load plus ivermectin can trigger a severe neurologic reaction. Mass programs in those belts screen or quantify before they dose. That does not make the drug globally reckless. It makes a travel and birth-country question mandatory before anyone treats onchocerciasis - or hands out a 'just in case' strip after a Central African trip.
For ordinary scabies or Strongyloides far from Loa belts, that hold is usually closed. For a person with the right map, it is the first sentence, not a footnote. Mention the countries. Mention the eye-worm stories. Then decide. The ivermectin medication page keeps the channel story and the tablet PK. This page keeps the hold on the map, where it belongs.
How a 'maybe ivermectin' consult should read
Bring a travel map, a stool or skin result if you have one, a full drug list, and the actual product in the house - human tablet or barn tube. That packet decides faster than a symptom list.
A clean ask sounds like: 'I have a positive Strongyloides antibody and prednisone starts in three weeks.' Or: 'The ward has crusted scabies and we need a same-night oral plan.' Or: 'I lived on a river in an onchocerciasis belt and my skin and eyes are in the note.' Those sentences name an organism or a mite density. They earn a weight, a mcg/kg line, and a follow-up date.
A muddy ask sounds like: 'Can I keep some for COVID?' 'My cousin uses horse paste monthly.' 'I itch and I already tried a leftover chip.' Those sentences name a rumor or a product. They earn a no, a redirect, or a proper mite exam - not a casual 3 mg strip. If the itch is scabies, treat the household and schedule the second dose. If it is not, stop shopping in the antiparasitic aisle.
If the real question is an erection tablet, you are in the wrong brief. Daily 2.5 versus Cialis 10 mg is a schedule fork, answered by Dr. Grant Whitfield. This page stays with organisms. Named reader questions sit with Dr. Noor Haddad below. Change a dose or start a tablet only after your own clinician owns the organism and the kilograms.
Consultation
Reader questions, answered
Answered by Dr. Noor Haddad, MD · Infectious disease & internal medicine
Inbox after this map: people want a tablet for a rumor. Named questions below - organism first, then the 3 mg count.
Leila Ortiz asksMy Strongyloides antibody came back positive but I feel fine. Does that alone earn Stromectol 3 mg?
Often it starts the workup, not the swallow. Antibody can linger after an old exposure, and labs vary. I still want the exposure story - birth country, soil, walking barefoot - plus stool if we can get it, and a look at whether steroids or chemo are coming. A high-probability host who will be immunosuppressed may earn treatment even when the gut is quiet, because hyperinfection is the bill we are trying not to pay. A low-probability host with a lonely antibody and no upcoming immune hit may need a second test, not an automatic chip count. Either way the product is the human 3 mg tablet at about 200 mcg/kg, empty stomach, then stool follow-up. Feeling fine is how this worm prefers to travel - it is not a reason to skip the conversation, and it is not a reason to self-dose from a leftover strip. Walk the result in with CDC parasite pages open and the ivermectin medication page for the weight bands.
Kenji Morita asksWhy does river blindness use about 150 mcg/kg when Strongyloides uses 200? Can I just take the higher number for both?
Those two numbers are labeled anchors for two organisms, not a 'more is safer' slider. Onchocerciasis is about 150 mcg/kg. Intestinal strongyloidiasis is about 200 mcg/kg. Same 3 mg tablet, different chip counts, both on an empty stomach with water. Using the Strongyloides number on an onchocerciasis plan is not clever rounding - it is off-label arithmetic unless your clinician has a reason. Using a random higher number because a forum said 'load the dose' is how people leave the human-tablet lane. If both parasites are in play, that is a specialist map, not a kitchen conversion. I write the organism on the line first, then the mcg/kg, then the tablet count from today's weight. I do not let patients average the two figures 'to be sure.'
Sabine Roux asksCan I give my leftover 3 mg tablets to my child for lice instead of buying the lotion?
Not as a home recipe. Oral ivermectin for lice is a clinician call, weight-based, and it is not the same product as the lice lotion that already has its own label. Children are not small adults with a halved chip. The 3 mg tablet is counted from kilograms, and many kids sit in the lowest weight bands - or below the chart. Leftovers also age, split badly, and travel between households without the second-dose and combing plan that actually clears nits. If the school note says lice, start with the labeled topical and the comb, not a purse tablet. If cream failed or the case is ugly, bring the child in and let someone own the arithmetic. Swallowing a leftover adult chip 'to be done with it' is how we get the wrong milligram in the wrong body.
Omar Farouk asksI have a work trip to West Africa next month. Should I take a preventive Stromectol 3 mg now?
A calendar is not an organism. West Africa is a large map - some belts matter for onchocerciasis, some for other parasites, some for none of this tablet's jobs. I do not hand out a spring 'just in case' swallow because a ticket was purchased. I ask which country, which river or rural work, how long, and whether Loa loa geography is in the mix. Preventive tourism dosing is how people invent a third indication the label never wrote. Travel medicine may recommend other prophylactics for other pathogens. That is a different drawer. If you return with skin, eye, or gut findings, we name those and then we count 3 mg chips. Before you fly, pack the usual travel clinic list - not a livestock tube and not a leftover Stromectol blister 'for luck.'
Greta Lind asksThe dermatologist said crusted scabies. Is that the same two-dose plan as ordinary itch?
Crusted disease is a mite city, not a few burrows. Ordinary classic scabies often still starts with permethrin, with oral ivermectin as a clinic add when cream is a bad fit or a household has to move together. Crusted cases usually need a thicker plan: more than one oral weight-based dose, topical treatment, and real infection-control - bedding, contacts, sometimes a ward protocol. Immunosuppression is a frequent roommate. So no, I do not photocopy the 'two swallows a week apart' note and call it done. I also do not let anyone substitute horse paste because 'it is the same molecule.' Same INN, wrong concentration, wrong species, no chip count. Human 3 mg tablets, kilograms on the scale, a calendar for repeats, and a check for new burrows versus the dead-mite itch that can last weeks. CDC scabies pages are the public map I send with the after-visit summary.
Pavel Horak asksA coworker swears livestock paste cleared his cold in a day. Why is that not evidence?
A cold ends in a day a lot of the time with tea and sleep. That is not a trial. Paste is built for a horse's kilograms. The human labeled dose is in micrograms per kilogram from a 3 mg tablet. Those are not interchangeable containers. Viral syndromes also have no chloride-channel target for this drug to jam, which is why COVID-era dish experiments that needed huge concentrations did not become a reason to treat respiratory season. Large randomized studies did not show a clinical win. Your coworker's story is a timing coincidence plus a dangerous product. If he is still using paste, he needs a human clinician, not a second tube. If he wants a cough plan, that is fluids, rest, and the usual respiratory drawer - not an antiparasitic. I will not bless a barn product because an anecdote was loud.
Yasmin Adeyemi asksPrednisone starts in four weeks for a flare. Should we clear Strongyloides first even without symptoms?
That is one of the few 'maybe treat the quiet worm' consults I take seriously. Autoinfection means a person can carry Strongyloides for years and look well. Steroids are a classic tripwire for hyperinfection. So I want the exposure history - tropics, subtropics, soil, older immigration story - and whatever serology or stool we can get before the first steroid dose. A plausible carrier may earn ivermectin at the Strongyloides 200 mcg/kg line now, with a plan to confirm clearance, rather than waiting for larvae in the lungs later. A person with no exposure story and negative workup does not earn a ritual tablet. The mistake I see is either ignoring the worm until the ICU or handing 3 mg to every incoming steroid script as a superstition. Name the risk, test what you can, treat when the probability is real. MedlinePlus is fine for the patient-facing worm summary; the timing call stays with the prescriber who owns the steroid.
Colin Briggs asksIs the rosacea cream my dermatologist gave me the same script as Stromectol 3 mg?
Same active ingredient, different job, different label, different way into the body. The cream is a skin-surface product for rosacea. Stromectol 3 mg is a systemic tablet counted from kilograms for named worms. You do not eat the cream to treat Strongyloides. You do not crush tablets onto a face to treat redness. If both are in the house, keep them in separate sentences: 'this is for my face' and 'this is for a documented parasite.' Mixing those sentences is how leftover chips get swallowed for a complexion, or cream gets treated like a cheap oral. Ask the dermatologist which product is which, and keep the tablet conversation on the organism map. I will not convert a rosacea tube into a travel-medicine plan.
Marisol Vega asksAfter the Strongyloides dose, how do I know the organism is actually gone?
The swallow is the start of clearance, not the certificate. The label still wants follow-up stool exams for intestinal disease. Antibody can lag and confuse people who want a single blood test to say 'done.' I schedule stool, I ask about gut and skin symptoms, and I keep the steroid or chemo calendar in view - because a missed load plus immunosuppression is the expensive miss. If stools stay positive, we do not shrug and buy paste. We rethink dose, timing, adherence, and whether the host is more complicated than the outpatient line. If you feel better the next morning, that is nice and it proves little. Worms this quiet do not send a thank-you note. Bring the lab slips back. That is how the map closes.
General education from a clinician, not personal medical advice. Bring your own history to your own prescriber.