Ivermectin
Is It Right for You?
A complete guide to Ivermectin — what it treats, how it works, dosages, side effects, and when a clinician may prescribe it following an online consultation.
What Is Ivermectin?
Ivermectin is a broad-spectrum antiparasitic medication that has been in clinical use since the 1980s. Derived from a compound produced by the soil bacterium Streptomyces avermitilis, it is one of the most important antiparasitic drugs ever developed and has been credited with dramatically reducing the global burden of several devastating parasitic diseases. Its discoverers were awarded the Nobel Prize in Physiology or Medicine in 2015 in recognition of its transformative impact on global health.
In the UK, ivermectin is used primarily to treat infestations of the skin mite Sarcoptes scabiei (scabies) -- both in individual patients and in institutional outbreaks -- as well as a range of parasitic worm (helminth) infections. It is highly effective against a wide variety of parasites, including nematodes (roundworms) and ectoparasites (external parasites such as mites and lice), though it has no activity against tapeworms or flukes.
Ivermectin is available as oral tablets and as a topical lotion. It is suitable for adults and children above a minimum weight threshold (typically 15 kg for oral use). It is available generically and under the brand name Stromectol (oral) and Sklice or Soolantra (topical formulations).
Oral ivermectin is a prescription-only medication in the UK. A licensed clinician must assess your symptoms and medical history before it can be prescribed -- which can now be done quickly and conveniently through a telehealth consultation.
Important: Ivermectin Is Not a Treatment for COVID-19 Despite widespread claims during the COVID-19 pandemic, ivermectin has not been shown to be effective for the prevention or treatment of COVID-19 in robust clinical trials. Major health authorities including the WHO, NHS, and MHRA do not recommend ivermectin for COVID-19 outside of clinical trials. Using ivermectin for this purpose -- particularly veterinary formulations -- carries serious risks. This page addresses ivermectin's licensed and evidence-based uses only.
What Conditions Is Ivermectin Used For?
Ivermectin is used to treat a range of parasitic infestations and infections:
the most common indication in the UK; oral ivermectin is used for the treatment of crusted (Norwegian) scabies, classical scabies where topical treatment has failed, and for mass treatment in institutional outbreaks (care homes, prisons, schools) where topical treatment is impractical; two doses are usually required 7--14 days apart.
topical ivermectin lotion is used for the treatment of head lice infestations, particularly where standard topical treatments (permethrin, malathion) have failed.
infection with the intestinal nematode Strongyloides stercoralis, which can cause a life-threatening hyperinfection syndrome in immunocompromised patients; ivermectin is the treatment of choice.
a parasitic infection caused by Onchocerca volvulus transmitted by blackflies; ivermectin is the cornerstone of global control programmes and the mainstay of individual treatment, preventing the progressive visual impairment caused by the parasite.
skin infestation caused by migrating hookworm larvae from soil contaminated with animal faeces; presents as intensely itchy, serpiginous (winding) tracks on the skin; ivermectin is highly effective.
For scabies and head lice, treating only the symptomatic individual is insufficient. All close contacts and household members must be treated at the same time -- regardless of whether they have symptoms -- to prevent reinfestation. Bedding, clothing, and towels used in the 72 hours before treatment should be washed at 60°C or above on the same day as treatment.
How Does Ivermectin Work?
Ivermectin works by selectively targeting ion channels that are found in invertebrates (parasites) but absent or structurally different in mammals, giving it a highly favourable therapeutic index -- effective against parasites at doses that are well tolerated by humans.
Ivermectin binds selectively and with very high affinity to glutamate-gated chloride ion channels (GluCl channels) -- a class of ion channel found exclusively in invertebrate nerve and muscle cells. These channels are not present in mammals, which explains ivermectin's selective toxicity to parasites. When ivermectin binds to these channels, it causes them to open irreversibly, allowing a sustained influx of chloride ions into the nerve and muscle cells of the parasite. This hyperpolarises the cell membrane, causing paralysis of the parasite's musculature and nervous system. The parasite becomes immobilised, cannot feed or reproduce, and dies or is expelled from the host.
Ivermectin also enhances the release of gamma-aminobutyric acid (GABA) at nerve junctions in parasites, further potentiating the paralytic effect. In mammals, GABA-mediated neurotransmission in the central nervous system is protected from ivermectin by the blood-brain barrier, which prevents the drug from reaching CNS GABA receptors at therapeutic doses. This is why ivermectin is safe for humans at standard doses but lethal to invertebrate parasites.
For rosacea, the mechanism is dual -- ivermectin's action against Demodex folliculorum mites (which are found in increased numbers on the skin of rosacea patients and may trigger inflammatory responses) combined with direct anti-inflammatory effects that reduce neutrophil activity and inflammatory cytokine release.
Dosages & Administration
The correct dose depends on the type and severity of infection, age, weight, and kidney function. Always follow your clinician's instructions. The table below is for general reference only.
Administration Tips
Oral ivermectin must be taken on an empty stomach, with water, at least 1 hour before food. Food -- particularly high-fat meals -- significantly increases ivermectin absorption and can raise blood levels to a degree that increases the risk of side effects. Consistent fasted administration is important for safe and predictable dosing.
Dosing is calculated by body weight. Your clinician will calculate the appropriate dose based on your weight. Tablets are available in fixed strengths (typically 3 mg), and doses are rounded to the nearest available tablet strength.
Both doses must be completed for scabies. A single dose of ivermectin for scabies kills the adult mites but does not reliably kill eggs. The second dose, given 7--14 days later, kills the newly hatched mites before they can mature and re-establish the infestation. Missing the second dose significantly increases the risk of treatment failure.
Topical ivermectin lotion (head lice): Apply to dry hair and scalp, leave for 10 minutes, then rinse thoroughly. A second application 7 days later is recommended to catch any hatching eggs. Do not use near eyes or on broken skin.
Environmental decontamination is essential for scabies. On the same day as treatment, wash all clothing, bed linen, and towels used in the past 72 hours at 60°C or above, and dry thoroughly. Items that cannot be washed should be sealed in a plastic bag for at least 72 hours (mites cannot survive off the human body for longer than this).
Side Effects of Ivermectin
Oral ivermectin is generally very well tolerated at the doses used for most indications. Side effects are typically mild and transient. Some reactions that occur following ivermectin treatment for filarial infections are caused not by the drug itself but by the immune response to dying parasites (Mazzotti reaction).
- Nausea
- Diarrhoea
- Dizziness or lightheadedness
- Headache
- Fatigue
- Pruritus (itching) -- can be a reaction to dying parasites rather than the drug itself
- Skin rash or urticaria
- Abdominal pain or discomfort
Mazzotti Reaction (Specific to Filarial Infections)
In patients being treated for onchocerciasis or lymphatic filariasis, the death of large numbers of microfilariae can trigger a systemic inflammatory response known as the Mazzotti reaction, characterised by:
- Fever
- Rash, intense itching, and skin oedema
- Lymph node swelling and tenderness
- Arthralgia and myalgia
- Hypotension (low blood pressure)
- Tachycardia
This reaction typically occurs within the first 24 hours of treatment and resolves spontaneously, but may require symptomatic treatment with antihistamines or corticosteroids in severe cases.
- Neurological toxicity -- confusion, ataxia (loss of coordination), tremor, encephalopathy; extremely rare at therapeutic doses in people with an intact blood-brain barrier; more likely in patients with very high parasite burdens (particularly Loa loa microfilaraemia), in patients with disrupted blood-brain barrier function, or with significant drug overdose
- Severe hypotension -- rare; more common in the context of heavy filarial parasite burden and Mazzotti reaction
- Severe allergic reaction -- urticaria, angioedema, difficulty breathing; rare but requires immediate emergency treatment
- Stevens-Johnson Syndrome -- very rare severe skin reaction; seek immediate care if blistering or widespread skin peeling develops
In regions where Loa loa (eye worm) is endemic (parts of central and west Africa), patients with very high Loa loa microfilaraemia (>30,000 microfilariae/mL) are at risk of serious and potentially fatal neurological reactions following ivermectin treatment. Pre-treatment testing for Loa loa microfilarial density is recommended in patients from endemic regions before ivermectin is administered for any indication.
Drug Interactions
Ivermectin has relatively few clinically significant drug interactions compared to many other medications. It is metabolised primarily by the liver enzyme CYP3A4 and is a substrate of the P-glycoprotein (P-gp) efflux transporter. Always disclose all medications to your clinician or pharmacist.
Ivermectin can enhance the anticoagulant effect of warfarin, increasing the risk of bleeding. INR should be monitored closely during and after ivermectin treatment in patients taking warfarin.
These drugs inhibit the metabolism of ivermectin, potentially raising blood levels significantly and increasing the risk of neurological side effects. Use with caution and inform your clinician of all medications.
P-gp normally limits ivermectin's penetration of the blood-brain barrier and controls its absorption. Inhibitors of P-gp can increase ivermectin blood levels and potentially enhance CNS penetration, increasing the risk of neurological toxicity.
These drugs accelerate ivermectin metabolism, reducing its blood levels and potentially decreasing its effectiveness. Dose adjustment or alternative treatment may be required.
Alcohol may enhance the CNS effects of ivermectin, including dizziness. Alcohol should be avoided or minimised during treatment.
Important Warnings
Although neurological toxicity is extremely rare at therapeutic doses in otherwise healthy patients, it can occur in patients with very high microfilarial burdens (particularly Loa loa), patients with compromised blood-brain barrier function (e.g. due to meningitis or head injury), and in significant overdose. Symptoms include confusion, ataxia, tremor, and encephalopathy. Any neurological symptoms following ivermectin treatment require immediate emergency medical evaluation.
Veterinary ivermectin products -- available for livestock and pets -- are not safe for human use. They are formulated at much higher concentrations than human preparations, are not quality-controlled for human consumption, and contain other ingredients not intended for human use. Serious poisoning and deaths have been reported following self-administration of veterinary ivermectin, including formulations promoted online as COVID-19 treatments. Always use only pharmaceutical-grade ivermectin prescribed by a licensed clinician.
A very common cause of apparent ivermectin treatment failure for scabies is reinfestation from untreated contacts rather than true drug failure. All household members and close physical contacts must be treated simultaneously on the same day, even if asymptomatic, and environmental decontamination must be carried out. Post-treatment itching can persist for up to 4 weeks after successful treatment due to the allergic response to dead mite proteins -- this does not indicate treatment failure and should not prompt immediate retreatment.
Oral ivermectin is not recommended for children weighing less than 15 kg, as safety data in this group are limited. For children below this weight threshold, alternative antiparasitic treatments should be used under medical guidance.
Ivermectin is not recommended during pregnancy, particularly in the first trimester, as animal studies have shown teratogenic effects at high doses and human safety data are limited. In global mass drug administration programmes, pregnant women are excluded from ivermectin treatment as a precaution. Ivermectin is excreted in breast milk in low concentrations; the WHO advises that breastfeeding mothers can be treated after the first week of the infant's life if the benefits outweigh the risks, but caution is warranted. Always consult your clinician.
Speak to a Clinician About Treatment
Getting advice no longer means sitting in a waiting room. Through The GP Service, you can consult with a licensed clinician in minutes — from home, on your lunch break, or wherever works for you. If treatment is clinically appropriate, your clinician can issue a prescription during the consultation. A consultation does not guarantee a prescription.
The treatment you need, when you need it.
Ivermectin FAQs
Yes. A licensed clinician can assess your symptoms and medical history via a telehealth consultation and prescribe ivermectin if clinically appropriate. For scabies, head lice, and other parasitic conditions, prescriptions are typically issued the same day. Your clinician will also advise on contact tracing, simultaneous treatment of household members, and environmental decontamination where relevant.
Ivermectin begins killing mites within hours of the first dose. However, itching can persist for up to 2--4 weeks after successful treatment, as the immune system continues to react to dead mite proteins and faeces in the skin. This does not mean treatment has failed. The second dose, given 7--14 days after the first, is essential to kill mites that have hatched from eggs since the initial treatment. If itching has not improved at all by 4 weeks after the second dose, consult your clinician.
The itching of scabies is primarily an allergic response to the mites, their eggs, and their faeces in the skin -- not simply a reaction to living mites. After successful treatment and death of the mites, the immune system continues to react to the remaining allergens until they are cleared from the skin, which takes 2--4 weeks. Antihistamines and emollients can help manage post-treatment itch. Do not assume the treatment has failed because itching continues in the weeks after treatment.
Yes -- this is one of the most important points in scabies management. Scabies mites can be transmitted by close and prolonged skin contact before symptoms appear. A person can carry and spread mites for 4--6 weeks before developing symptoms (primary infestation). If only the symptomatic person is treated, reinfestation from untreated contacts is very likely. All household members and close physical contacts must be treated simultaneously, regardless of whether they have symptoms.
No. Oral ivermectin is a prescription-only medication in the UK. Topical ivermectin lotion for head lice (Hedrin Once) is available over the counter, as is ivermectin cream for rosacea (Soolantra) -- though the latter typically requires a prescription. Oral ivermectin must only be obtained through a licensed clinician. Products sold online without prescription -- including many promoted for COVID-19 -- are not regulated pharmaceutical-grade medications and may be dangerous.
Oral ivermectin tablets are used for systemic parasitic infections including scabies (particularly where topical treatment has failed or in institutional outbreaks), strongyloidiasis, onchocerciasis, and other helminth infections. Topical ivermectin cream (Soolantra 1%) is used specifically for the inflammatory lesions of rosacea and works locally on the skin. Topical ivermectin lotion is used for head lice. The formulation your clinician prescribes will depend entirely on your specific condition.
Oral ivermectin is not recommended for children weighing less than 15 kg due to limited safety data in this weight group. For children above 15 kg, ivermectin can be prescribed with weight-based dosing. Topical ivermectin lotion for head lice is licensed for children aged 6 months and above. Your clinician will advise on the most appropriate treatment for children based on their age and weight.
Permethrin 5% cream is the standard first-line topical treatment for scabies in the UK. It is applied to the whole body from the neck down, left on for 8--12 hours, and repeated after 7 days. Oral ivermectin is used when topical treatment has failed, when the patient cannot apply topical treatment effectively (due to mobility or cognitive issues), in crusted scabies, or in institutional outbreaks where simultaneous topical treatment of many individuals is impractical. In crusted scabies, oral ivermectin and topical permethrin are used together, as either alone is insufficient to eradicate the very high mite burden.