Ivermectin: Uses, Dosage, Side Effects, and Everything You Need to Know (UK Guide)

what is ivermectin used for in the UK?

Ivermectin is an antiparasitic medicine used to treat infections caused by certain worms and mites. In the United Kingdom, only one ivermectin product holds a UK marketing authorisation: Soolantra 10 mg/g cream, a topical treatment for the inflammatory spots of rosacea. Ivermectin tablets are not licensed in the UK — they can only be obtained on prescription as an unlicensed imported medicine, usually arranged by a hospital specialist for conditions such as strongyloidiasis, onchocerciasis, or crusted scabies.

Key takeaways

• Ivermectin is a macrocyclic lactone antiparasitic derived from soil bacteria, discovered in the 1970s and awarded a share of the 2015 Nobel Prize in Physiology or Medicine.
• It paralyses parasites by acting on nerve and muscle channels that mammals largely do not have — which is why it can be safe for people and lethal for worms and mites.
• In the UK, the topical cream (Soolantra) is licensed for papulopustular rosacea. Oral tablets are unlicensed and specialist-initiated.
• Typical oral dosing is weight-based, around 200 micrograms per kilogram, but regimens vary considerably by condition.
• Most side effects are mild and short-lived. The serious risks are concentrated in specific populations — particularly people who may be co-infected with Loa loa.
• For scabies in the UK, first-line treatment is topical permethrin or malathion, not ivermectin.
• Large randomised trials, including the UK's own PRINCIPLE trial, found no clinically meaningful benefit for COVID-19.

What exactly is ivermectin?

Ivermectin belongs to a family of compounds called the avermectins. Its origin story is one of the more remarkable in modern pharmacology.

In the 1970s, the Japanese microbiologist Satoshi Ōmura was systematically screening soil bacteria for useful compounds. From a sample collected near a golf course in Kawana, Japan, he isolated a previously unknown organism, Streptomyces avermitilis. Working with William C. Campbell at Merck in the United States, the team found that the compounds it produced were devastatingly effective against parasitic worms. Chemical modification produced ivermectin — more potent and better tolerated than the parent compound.

The impact was extraordinary. Ivermectin became the backbone of mass drug administration programmes against river blindness (onchocerciasis) and lymphatic filariasis across sub-Saharan Africa and Latin America. Merck's Mectizan Donation Programme, launched in 1987, has distributed billions of treatments free of charge. In 2015, Ōmura and Campbell shared the Nobel Prize in Physiology or Medicine for the discovery, alongside Tu Youyou for artemisinin.

Ivermectin sits on the World Health Organization's Model List of Essential Medicines. It is, by any reasonable measure, one of the most consequential medicines of the twentieth century — which is precisely why the misinformation attached to it since 2020 has been so frustrating for the clinicians and researchers who use it properly.

How does ivermectin work?

Understanding the mechanism explains both why it works and where its risks lie.

Invertebrates — worms, mites, insects — have glutamate-gated chloride channels (GluCl) in their nerve and muscle cells. Ivermectin binds to these channels with high affinity and holds them open. Chloride ions flood in, the cell hyperpolarises, and the parasite is paralysed. It can no longer feed, move, or reproduce, and it dies. Ivermectin also interacts with GABA-gated chloride channels in some organisms, contributing to the same effect.

Mammals do not have glutamate-gated chloride channels of this type. We do have GABA-gated chloride channels — but they sit almost entirely within the central nervous system, behind the blood–brain barrier. A transporter protein called P-glycoprotein actively pumps ivermectin back out of the brain, keeping central nervous system concentrations very low.

This is the entire basis of ivermectin's safety margin in humans. It is also why two situations raise concern:

1. Very high doses, which can overwhelm P-glycoprotein transport.

2. Drugs or genetic variants that impair P-glycoprotein function, potentially allowing more ivermectin into the brain. (This is well documented in certain collie dog breeds with an MDR1 gene mutation, which is why ivermectin-containing veterinary products carry breed warnings.)

There is a third, separate mechanism relevant to the cream: in rosacea, ivermectin appears to work both by killing Demodex folliculorum mites — present in higher densities in rosacea-affected skin — and through a direct anti-inflammatory effect on the skin.

Licensed and unlicensed uses of ivermectin in the UK

This is where UK readers often get confused, because most online information about ivermectin is written for a US audience where oral tablets are FDA-approved and widely stocked. The UK situation is different.

The one licensed product: Soolantra (topical)

Soolantra 10 mg/g cream (ivermectin 1%) is licensed by the MHRA for the topical treatment of inflammatory lesions of papulopustular rosacea in adults. It is prescription-only. Local NHS formularies generally position it as an option for the spots and pustules of rosacea, with treatment reviewed after three months and typically not continued beyond four months in a single course.

It is worth being clear about what it does and does not treat: Soolantra targets the papules and pustules of rosacea. It is not a treatment for the persistent facial redness (erythema) or visible thread veins, which are managed differently — with topical brimonidine, laser or intense pulsed light therapy, and trigger avoidance.

Unlicensed oral use: how it actually works in practice

Ivermectin tablets — sold in France and elsewhere as Stromectol 3 mg — have never held a UK marketing authorisation. The MHRA has confirmed that no manufacturer has applied for one.

This does not mean UK patients cannot access it. UK prescribers may lawfully prescribe an unlicensed medicine, or import one on a "named-patient" basis, where in their clinical judgement no suitable licensed alternative meets a patient's needs. In practice, oral ivermectin in the UK is usually:

• Initiated by a specialist : most often in infectious diseases, tropical medicine, or dermatology.
• Sourced through a specialist importer or a hospital pharmacy.
• Accompanied by explicit counselling that the medicine is unlicensed in the UK.

Major centres such as the Hospital for Tropical Diseases in London and the Liverpool School of Tropical Medicine handle a large share of these cases.

Conditions oral ivermectin is used for :

Important: scabies treatment in the UK

If you have been diagnosed with ordinary scabies, your GP will almost certainly prescribe permethrin 5% cream first, or malathion 0.5% aqueous liquid if permethrin is unsuitable. These are the UK first-line treatments. Ivermectin tablets tend to be reserved for crusted scabies, institutional outbreaks (care homes, for example), people who cannot apply topical treatment properly, or repeated treatment failure.

Recent UK supply problems with permethrin have increased interest in oral ivermectin, but the decision remains a clinical one made by your prescriber.

Ivermectin dosage: what the regimens look like

Read this section as background, not as instructions. Ivermectin dosing is weight-based and condition-specific, and getting it wrong matters. Follow the regimen your prescriber gives you.

 Oral dosing principles

Oral ivermectin is dosed in micrograms per kilogram of body weight, most commonly 200 micrograms/kg. For a 70 kg adult that works out at roughly 14 mg — around four or five 3 mg tablets. Doses are rounded to whole tablets, which is why tablet counts step up in bands rather than smoothly.

Approximate regimens used internationally:

The repeat dose in scabies matters. Ivermectin kills mites but has limited effect on unhatched eggs. A second dose about a week later kills mites that hatched after the first.

How to take the tablets

The French Stromectol summary of product characteristics advises taking tablets with water on an empty stomach, at least one hour before food. Some clinicians deliberately give it with a fatty meal to increase absorption, since food substantially increases bioavailability — but that is a specialist judgement, not something to improvise.

Do not drink alcohol around the time of dosing. Alcohol may increase plasma concentrations and worsen dizziness.

Topical dosing (Soolantra)

Apply a pea-sized amount to each of five areas — forehead, chin, nose, and each cheek — then spread as a thin layer across the whole face, once daily, avoiding eyes, lips, and mucous membranes. Wash and dry the face first, and let it dry before applying make-up. Improvement is usually gradual over several weeks. If there has been no improvement after three months, treatment is normally stopped.

If you miss a dose

For the cream, apply the next dose as normal — do not double up. For a course of tablets, contact your prescriber for advice rather than guessing, particularly for multi-day regimens in crusted scabies.

Ivermectin side effects

Most people who take ivermectin at standard doses tolerate it well. Side effects fall into distinct categories.

Common side effects (oral)

These are usually mild and settle within a day or two:

• Dizziness or light-headedness
• Nausea, vomiting, diarrhoea, or abdominal discomfort
• Loss of appetite
• Headache and tiredness
• Muscle aches or joint pain
• Itching or mild rash

Because dizziness and drowsiness are possible, do not drive or operate machinery until you know how it affects you.

Common side effects (Soolantra cream)

• Burning or stinging sensation on application.
• Skin irritation, dryness, or flaking.
• Itching.
• Temporary worsening of rosacea in the first few weeks.

The last of these catches people out. A transient flare early in treatment is recognised and usually settles. If it is severe or persists, speak to your prescriber.

The Mazzotti reaction

When ivermectin is used to treat onchocerciasis, the dying microfilariae release antigens that trigger an inflammatory response — the Mazzotti reaction. Symptoms include fever, intense itching, rash, swollen and tender lymph nodes, joint pain, headache, and occasionally low blood pressure. It typically appears within a day or two of dosing and is more severe with heavier parasite loads.

This is a reaction to parasite death, not an allergy to the drug. It is anticipated and managed by treating clinicians, sometimes with antihistamines or corticosteroids.

The serious risk: Loa loa co-infection

The most important safety issue with ivermectin is severe encephalopathy in people co-infected with Loa loa (African eye worm), particularly those with very high microfilarial loads in the blood. Rapid killing of large numbers of microfilariae can cause a serious, occasionally fatal neurological reaction.

This is why anyone who has lived in or travelled extensively through the loiasis belt of Central and West Africa should be screened for Loa loa microfilaraemia before receiving ivermectin. It is one of several reasons oral ivermectin is a specialist medicine rather than a repeat-prescription item.

Rare but serious reactions

Seek urgent medical attention for:

• Signs of a severe allergic reaction — swelling of the face, lips, tongue, or throat; difficulty breathing; widespread hives
• Severe blistering or peeling of the skin or mucous membranes (possible Stevens–Johnson syndrome or toxic epidermal necrolysis)
• Yellowing of the skin or eyes, dark urine, or severe upper abdominal pain (possible liver injury)
• Seizures, confusion, or marked unsteadiness

Who should avoid ivermectin?

• Known hypersensitivity to ivermectin or any excipient
• Children weighing under 15 kg, where safety data are limited
• Pregnancy — data are limited and treatment is usually deferred where possible; the WHO has historically excluded pregnant women from mass drug administration
• Breastfeeding — small amounts pass into breast milk; discuss with your clinician
• Significant liver impairment, since ivermectin is metabolised hepatically
• Possible Loa loa exposure, until screening is complete

Interactions worth flagging

• Warfarin  — cases of altered anticoagulation have been reported; INR monitoring is sensible
• Strong P-glycoprotein inhibitors (for example ciclosporin, verapamil, some antivirals) — theoretically increase brain penetration
• CYP3A4 inhibitors — may raise plasma levels
• Sedatives, benzodiazepines, sodium oxybate — potential additive central nervous system effects
• Alcohol — may increase plasma concentrations

Always give your prescriber and pharmacist a full list of your medicines, including supplements and anything bought over the counter.

The veterinary ivermectin warning

This needs stating plainly. Do not take ivermectin products intended for animals.

Veterinary formulations — horse wormer pastes, cattle pour-on solutions, sheep drenches — are dosed for animals weighing several hundred kilograms. They are far more concentrated than human preparations, and they contain excipients that have never been assessed for human ingestion.

Reported consequences of taking veterinary ivermectin include vomiting, diarrhoea, low blood pressure, confusion, ataxia, hallucinations, seizures, and coma. Poison centres in several countries recorded sharp increases in ivermectin-related calls during 2021.

Equally, be cautious about unregulated online sellers. A number of websites advertise ivermectin tablets to UK customers "without prescription". Buying prescription medicines this way means no clinical oversight, no Loa loa screening, no interaction check — and no guarantee that the tablets contain what the label claims. Counterfeit and substandard products are a documented problem. If you buy from a UK online pharmacy, check that it is registered with the General Pharmaceutical Council and displays the appropriate registration logo.

Storage and practical points

• Store both tablets and cream below 25–30°C, away from direct sunlight and moisture. Do not keep medicines in a steamy bathroom.
• Keep out of sight and reach of children.
• Return unused or expired medicine to a pharmacy for disposal — do not flush it or put it in household waste.
• For scabies, treat all household members and close contacts simultaneously, even if they have no symptoms, and wash bedding, towels, and clothing at 60°C. Treating one person alone almost guarantees reinfestation.