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Derbac M Liquid - 150ml

Derbac M Liquid - 150ml

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  • ✔️ Kills both live head lice and eggs with one treatment
  • ✔️ Contains malathion 0.5% — clinically proven insecticide
  • ✔️ Treats head lice and scabies in a single product
  • ✔️ Suitable for adults and children aged 6 months and over
  • ✔️ 150ml bottle provides enough for multiple applications

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Is Derbac M Liquid Head Lice Treatment Right for You?

 

Head lice are one of the most common childhood complaints in the UK, affecting millions of families every year. If you've spotted the telltale signs — persistent scalp itching, tiny white eggs (nits) clinging to hair shafts, or live lice moving through the hair — you'll want something that actually works. Derbac M liquid head lice treatment is a clinically established, malathion-based lotion that kills both live lice and their eggs in a single overnight application. You can find it alongside other head lice treatments at Cured Pharmacy, available without a prescription.

Derbac M Liquid contains malathion 0.5% w/v as its active ingredient. It comes in a 150ml bottle — enough to treat the whole family if needed. It's been used in the UK for decades and remains one of the recommended insecticide-based options for head lice management.

 

How Does Derbac M Liquid Work Against Lice and Scabies?

 

Malathion is an organophosphate compound. It works by inhibiting acetylcholinesterase, an enzyme that lice and mites depend on for normal nerve function. When this enzyme is blocked, the parasite's nervous system is overwhelmed, leading to paralysis and death. Crucially, malathion is effective against both live lice and their eggs (nits), which is why a second application is still recommended after seven days — to catch any eggs that may have hatched in the interim.

  • Inhibits acetylcholinesterase in lice and scabies mites
  • Causes neuromuscular paralysis in the parasite
  • Active against both adult lice and viable eggs
  • Absorbed through the parasite's exoskeleton on contact

 

Who Should Use Derbac M Liquid?

 

Derbac M Liquid is suitable for most adults and children aged 6 months and over. It's particularly useful when wet combing alone hasn't cleared an infestation, or when a chemical treatment is preferred. It can also be used to treat scabies — a separate skin condition caused by the Sarcoptes scabiei mite — under appropriate guidance.

  • Adults and children aged 6 months and over with confirmed head lice
  • Individuals with scabies (under pharmacist or GP guidance)
  • Households where multiple family members need treatment simultaneously
  • Those who have not responded to physical (dimeticone-based) treatments

 

How Does Derbac M Liquid Compare to Alternative Head Lice Treatments?

 

Feature Derbac M Liquid Hedrin (Dimeticone)
Active ingredient Malathion 0.5% Dimeticone 4% or 92%
Mechanism Chemical (insecticide) Physical (suffocation)
Kills eggs? Yes Yes (with repeat application)
Application time 12 hours (overnight) 8 hours or 15 minutes (varies by product)
Suitable for scabies? Yes No

 

Is Derbac M Liquid Safe to Store at Home?

 

Yes — but there are a few important points to keep in mind. Derbac M liquid head lice treatment is flammable, so you must keep it away from naked flames, cigarettes, and heat sources during application and while the hair is drying. Never use a hairdryer after applying it. Store the bottle below 25°C, away from direct sunlight, and always keep it out of reach of children. If you're looking for other topical treatments for skin conditions, you might also want to browse our range of creams and ointments.

This product is a medicine. Speak to your doctor or pharmacist before using if you have an underlying medical condition or are taking other medicines.

Derbac M Liquid 150ml specifications
Treatment category Head lice and scabies
Active ingredient Malathion 0.5% w/v
Mechanism of action Acetylcholinesterase inhibitor (organophosphate insecticide)
Effective against Head lice (Pediculus humanus capitis), scabies mites (Sarcoptes scabiei)
Suitable for Adults and children aged 6 months and over
Pack size 150ml
UK classification Pharmacy (P) medicine
Drug class Organophosphate insecticide
Preparation Aqueous lotion
Route of administration Topical (cutaneous)

Specifications of Derbac M Liquid 150ml

 

What Is Derbac M Liquid and What Is It Used For?

 

Derbac M Liquid is a topical aqueous lotion containing malathion 0.5% w/v. It is used to treat two parasitic conditions: head lice infestations (pediculosis capitis) and scabies. Head lice are tiny insects that live on the scalp and feed on blood; scabies is caused by a microscopic mite that burrows into the skin, causing intense itching. Both conditions are common in the UK and are not a sign of poor hygiene. The NHS recommends treating head lice as soon as they are detected to prevent spread to others.

Derbac M Liquid is classified as a Pharmacy (P) medicine in the UK, meaning it is available without a prescription but should be purchased from a registered pharmacy. It is suitable for adults and children aged 6 months and over. If you're managing other skin-related conditions alongside head lice, our skin care range may also be of interest.

 

What Do You Need to Know Before Using Derbac M Liquid?

 

Before applying Derbac M Liquid, read the following contraindications and warnings carefully:

  • Do not use if you are allergic to malathion or any other ingredient in the product
  • Do not apply to broken, infected, or inflamed skin
  • Avoid contact with eyes — rinse immediately with water if contact occurs
  • Do not use on children under 6 months without medical supervision
  • Do not use near naked flames or heat sources — the lotion is flammable
  • Do not use a hairdryer to dry hair after application
  • Consult your doctor or pharmacist if you are pregnant or breastfeeding before use
  • People with asthma may be more sensitive to the product — seek advice before use

Drug interactions with topical malathion are not clinically significant in normal use. However, you should inform your pharmacist of any other medicines you are using, particularly other topical treatments applied to the same area.

  • No significant interactions with oral medicines are expected at topical doses
  • Avoid concurrent use of other scalp treatments unless advised by a healthcare professional

 

How Should You Use Derbac M Liquid?

 

Follow these steps carefully to ensure the treatment is as effective as possible. All members of the household with confirmed lice should be treated at the same time to prevent re-infestation.

  1. Check the hair and scalp carefully using a fine-toothed detection comb to confirm live lice are present
  2. Apply Derbac M Liquid to dry hair — part the hair into sections and work the lotion into the scalp and along the full length of the hair
  3. Pay particular attention to the nape of the neck and behind the ears, where lice tend to congregate
  4. Allow the hair to dry naturally in a well-ventilated room — do not use a hairdryer
  5. Leave the lotion on for 12 hours (overnight is ideal)
  6. Wash the hair thoroughly with a normal shampoo and rinse well
  7. Use a fine-toothed nit comb to remove dead lice and eggs from the hair
  8. Repeat the entire process after 7 days to kill any lice that may have hatched from eggs since the first treatment
Indication Age Group Dose Frequency
Head lice Adults and children ≥6 months Sufficient to cover scalp and hair Two applications, 7 days apart
Scabies Adults and children ≥6 months Apply to whole body below neck (and face/scalp in children) As directed by a healthcare professional
Children under 6 months Under 6 months Only under medical supervision As directed by a doctor

 

What Are the Possible Side Effects of Derbac M Liquid?

 

Side effects with Derbac M Liquid are uncommon when used as directed. Most people tolerate it well. However, as with any medicine, some individuals may experience unwanted effects.

Common side effects:

  • Mild stinging or burning sensation on the scalp
  • Temporary skin redness at the application site
  • Scalp irritation or dryness

Less common side effects:

  • Contact dermatitis (skin rash or inflammation)
  • Allergic skin reactions such as itching or hives
  • Eye irritation if the product accidentally contacts the eyes

Serious allergic reactions (anaphylaxis) are rare but possible. Seek immediate medical attention if you experience swelling of the face, lips, or throat, difficulty breathing, or a severe rash. If you're also dealing with itching from other causes, our hair care range includes products that may help soothe the scalp after treatment.

 

How Should You Store Derbac M Liquid?

 

  • Store below 25°C in a cool, dry place
  • Keep away from direct sunlight and heat sources
  • Keep the bottle tightly closed when not in use
  • Keep out of reach and sight of children
  • Do not store near naked flames — the product is flammable
  • Do not use after the expiry date printed on the bottle
  • Do not dispose of medicines via wastewater or household waste — return unused product to your pharmacy

Written and reviewed by our qualified team

Your safety and success are our highest priorities. Our medical team rigorously evaluates every product and piece of advice we provide, ensuring you receive only the most effective, science-backed solutions available.

Frequently Asked Questions

Where can I buy Derbac M Liquid online in the UK?

You can buy Derbac M Liquid 150ml directly from Cured Pharmacy, a GPhC-registered online pharmacy. It is available over the counter without a prescription. Simply add it to your basket and choose your preferred UK delivery option at checkout.

How does Derbac M Liquid work against head lice?

Derbac M Liquid contains malathion 0.5%, an organophosphate insecticide that inhibits acetylcholinesterase — an enzyme essential to the nervous system of lice and mites. This causes paralysis and death of both adult lice and their eggs. It is one of the insecticide-based options recommended by the NHS for treating head lice infestations.

How do I use Derbac M Liquid step by step?

Apply the lotion to dry hair, working it thoroughly into the scalp and along the full length of the hair. Allow it to dry naturally — never use a hairdryer — and leave it on for 12 hours or overnight. Wash off with normal shampoo, comb through with a nit comb, and repeat the whole process after 7 days.

How long do I leave Derbac M Liquid on my hair?

You should leave Derbac M Liquid on the hair and scalp for a minimum of 12 hours. Most people find it easiest to apply it in the evening and wash it off the following morning. Leaving it on for the full duration gives the malathion enough contact time to kill both live lice and eggs effectively.

Is Derbac M Liquid safe for children?

Yes — Derbac M Liquid is suitable for adults and children aged 6 months and over. For children under 6 months, treatment should only be carried out under the supervision of a doctor. Always keep the lotion away from a child's eyes and mouth during application, and ensure the room is well ventilated.

Can I use Derbac M Liquid if I am pregnant or breastfeeding?

If you are pregnant or breastfeeding, you should speak to your doctor or pharmacist before using Derbac M Liquid. Topical malathion is absorbed through the skin in small amounts, and while the risk is considered low, professional guidance is always recommended during pregnancy and lactation. Your pharmacist can help you weigh up the options.

What are the side effects of Derbac M Liquid?

Side effects are uncommon but can include mild scalp stinging, redness, or skin irritation at the application site. Allergic reactions such as a rash or hives are rare. If you experience swelling of the face or throat, or difficulty breathing, stop using the product and seek urgent medical attention.

What is the difference between Derbac M Liquid and Hedrin?

Derbac M Liquid uses malathion, a chemical insecticide that kills lice by disrupting their nervous system. Hedrin uses dimeticone, a silicone-based oil that physically coats and suffocates lice without using a chemical insecticide. Both are effective treatments; the choice often depends on personal preference or whether lice in your area have developed resistance to insecticides. You can browse our full range of head lice treatments to compare options.

Can Derbac M Liquid be used to treat scabies?

Yes — malathion, the active ingredient in Derbac M Liquid, can be used to treat scabies as well as head lice. For scabies, the lotion is applied to the whole body below the neck (and to the face and scalp in young children), left on for the recommended period, and then washed off. Always follow the guidance of your pharmacist or GP for scabies treatment, as the application method differs from head lice treatment.

Why do I need to apply Derbac M Liquid twice?

The first application kills live lice and most eggs. However, some eggs may survive and hatch within the following week. The second application, carried out exactly 7 days after the first, targets any newly hatched lice before they have a chance to mature and lay new eggs. Skipping the second treatment significantly increases the risk of re-infestation.

Is Derbac M Liquid flammable?

Yes — Derbac M Liquid is flammable. You must keep it away from naked flames, lit cigarettes, and any heat sources during application and while the hair is drying. Never use a hairdryer after applying the lotion. Allow the hair to dry completely in a well-ventilated room before going near any open flame.

How do I know if the head lice treatment has worked?

After completing both applications (7 days apart), check the hair carefully using a fine-toothed detection comb. If you find no live lice 2–3 days after the second treatment, the infestation has likely been cleared. Dead lice and empty egg cases (nits) may still be visible in the hair but are harmless. If live lice are still present, consult your pharmacist about alternative treatments.

Who is eligible to use Derbac M Liquid?

Derbac M Liquid is suitable for most adults and children aged 6 months and over who have a confirmed head lice infestation or scabies. It is not suitable for people with a known allergy to malathion or any other ingredient in the product. Those with asthma, broken skin on the scalp, or who are pregnant should seek pharmacist advice before use. If you're also looking for products for younger children, our baby and toddler range may be helpful.

What are the alternatives to Derbac M Liquid for head lice?

Alternatives include dimeticone-based products (such as Hedrin), wet combing with a fine-toothed comb (the Bug Busting method), and other insecticide-based treatments such as permethrin. The NHS recommends rotating between different types of treatment if one does not appear to be working, as resistance to insecticides can develop. Speak to your pharmacist for personalised advice.

What are the latest recommendations on head lice treatment in the UK?

The NHS currently recommends either wet combing or a medicated lotion as the two main approaches to treating head lice. Malathion-based treatments like Derbac M Liquid remain on the NHS recommended list, alongside dimeticone products. The NHS advises treating only confirmed live infestations — not as a preventive measure — and treating all affected household members at the same time to avoid re-infestation.

How Should You Use Derbac M Liquid?

Always apply Derbac M Liquid to dry hair — not damp or wet hair — as water can reduce the effectiveness of the lotion. Make sure you are in a well-ventilated room throughout the process, and keep the product away from the eyes and mouth at all times.

What Is the Correct Dose of Derbac M Liquid?

There is no fixed volume dose — you should use enough lotion to cover the entire scalp and hair thoroughly. For longer or thicker hair, more product will be needed. The 150ml bottle is generally sufficient for multiple applications or for treating more than one person.

When Is the Best Time to Use Derbac M Liquid?

Evening application is strongly recommended, as the lotion needs to remain on the hair for 12 hours. Applying it before bed means you can wash it off the following morning without disrupting your daily routine. Ensure the hair is completely dry before sleeping to avoid transferring the product to pillowcases unnecessarily.

Treat all affected household members on the same day to prevent lice passing back and forth between people. Check other family members' hair with a detection comb before deciding whether they also need treatment.

How Long Can You Use Derbac M Liquid For?

A standard course of treatment consists of two applications, seven days apart. You should not use Derbac M Liquid more frequently than this without pharmacist or GP guidance. If live lice are still present after completing both applications, consult your pharmacist — they may recommend switching to a different type of treatment, such as a dimeticone-based product, to address potential insecticide resistance.

Derbac M Liquid is intended for short-term use to treat an active infestation. It should not be used as a preventive measure or applied routinely. If infestations recur frequently, speak to your GP or pharmacist about the best management strategy for your household.

Do not exceed the recommended dose. If in doubt, speak to your pharmacist.

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What Are the Most Common Side Effects of Derbac M Liquid?

Most people who use Derbac M Liquid do not experience significant side effects. When reactions do occur, they are usually mild and localised to the area of application. The most frequently reported effects relate to the scalp and skin.

  • Mild stinging or burning sensation on the scalp during or after application
  • Temporary redness or warmth of the skin at the application site
  • Scalp dryness or a feeling of tightness after washing off the lotion

What Are the Less Common Side Effects of Derbac M Liquid?

Less commonly, some individuals may develop a more pronounced skin reaction. These effects are still generally mild but should be monitored. If they persist or worsen, stop using the product and seek pharmacist advice.

  • Contact dermatitis — a red, itchy, or inflamed skin rash at the site of application
  • Urticaria (hives) — raised, itchy welts on the skin
  • Eye irritation if the lotion accidentally contacts the eyes — rinse immediately with plenty of water
  • Hair or scalp discomfort lasting beyond the treatment period

What Are the Serious Side Effects of Derbac M Liquid?

Serious side effects are rare with topical malathion used as directed. However, a severe allergic reaction (anaphylaxis) is possible in individuals with a hypersensitivity to malathion or any other ingredient in the product. Symptoms of a serious allergic reaction include swelling of the face, lips, tongue, or throat, difficulty breathing or swallowing, a rapid heartbeat, or a sudden drop in blood pressure. This is a medical emergency — call 999 or go to your nearest A&E immediately if you experience these symptoms.

What Should You Do If You Experience Side Effects?

For mild side effects such as scalp stinging or redness, these usually resolve on their own once the product is washed off. Avoid scratching the affected area, as this can worsen irritation. If you develop a skin rash or persistent irritation, stop using the product and consult your pharmacist or GP. Always report unexpected or severe reactions to your healthcare provider.

You can also report suspected side effects directly to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk. This helps improve the safety monitoring of medicines available in the UK.

Can Derbac M Liquid Interact With Other Medicines?

Clinically significant drug interactions with topical malathion are not expected at the doses used for head lice or scabies treatment. The amount of malathion absorbed through the skin is very small. However, you should inform your pharmacist if you are using any other topical treatments on the same area of skin, as combining products may increase the risk of irritation. People with a history of sensitivity to organophosphate compounds should exercise caution and seek professional advice before use.

If you are concerned about any side effects, contact your pharmacist or GP immediately.

Patient Information Leaflet

Important - Before taking any medication, it is always important to read the Patient Information Leaflet (PIL)

Written and reviewed by our qualified team

GPhC Number: 2233073
Tarun Kumar

Reviewed by:

Tarun Kumar

Superintendent/ Clinical Lead

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Content last updated: 31 Mar 2025

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