Skip to product information
1 of 1

  • Images are for illustration purposes only

Derbac M Liquid -150ml

Derbac M Liquid -150ml

  • 1. Ozempic®️-equivalent therapy now available for weight management
  • 2. Average weight loss of 17%, with 1 in 3 patients achieving over 20%
  • 3. May help reduce osteoarthritis-related pain
  • 4. Wegovy®️ is not expected to impact the effectiveness of oral contraceptives
  • 5. Supports cardiovascular risk reduction
  • 6. Over 22 million patients treated with semaglutide-based therapies since 2018

  • ✔️ Kills both live head lice and eggs with one course
  • ✔️ Contains malathion 0.5% — clinically proven pediculicide
  • ✔️ Suitable for adults and children aged 6 months and over
  • ✔️ 150ml bottle — enough to treat the whole family
  • ✔️ Two-application course clears infestations in 14 days

Price Checker

Regular price £19.49
Sale price £19.49
Sale Sold out
  • Lowest price guarantee
  • Includes FREE private prescription
View full details

 

What Is Derbac M Liquid Head Lice Treatment?

 

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 — an itchy scalp, tiny eggs clinging to hair shafts, or live lice — you'll want something that actually works. Derbac M liquid head lice treatment is a well-established, clinically proven option available over the counter, containing malathion 0.5% w/v as its active ingredient. It's been used in the UK for decades and remains a recommended choice by NHS guidance for treating both head lice and pubic lice.

Derbac M Liquid comes in a 150ml bottle, giving you enough product to treat the whole family if needed. It's suitable for adults and children aged 6 months and over, making it a practical choice for households dealing with a lice outbreak. You can browse our full range of head lice treatments if you'd like to compare options before purchasing.

 

How Does Derbac M Liquid Work Against Lice?

 

Malathion, the active ingredient in Derbac M Liquid, belongs to a class of compounds called organophosphates. It works by disrupting the nervous system of head lice and their eggs. Here's what happens at a biological level:

  • Malathion inhibits the enzyme acetylcholinesterase in lice, which is essential for normal nerve function.
  • Without this enzyme, nerve signals cannot be properly terminated, causing continuous nerve firing.
  • This leads to paralysis and death of both live lice and, importantly, their eggs (nits).
  • The lotion formulation ensures good contact with the scalp and hair shaft, where lice and eggs are found.

Because Derbac M Liquid is pediculicidal (kills lice) and ovicidal (kills eggs), a single course of two applications — seven days apart — is usually sufficient to break the lice life cycle.

 

Who Should Use Derbac M Liquid?

 

This treatment is appropriate for a wide range of people. It's particularly useful when wet combing alone hasn't cleared the infestation, or when a quick, reliable solution is needed. Derbac M Liquid is suitable for:

  • Adults and children aged 6 months and over with confirmed head lice.
  • People who have tried wet combing without success.
  • Households where multiple family members need treatment simultaneously.
  • Individuals with pubic lice (crabs), as directed by a healthcare professional.

It is not recommended for infants under 6 months without medical supervision. People with known sensitivity to malathion or any other ingredient should avoid this product.

 

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

 

Feature Derbac M Liquid Dimeticone (e.g. Hedrin)
Active ingredient Malathion 0.5% Dimeticone 4% or 92%
Mechanism Neurotoxic — inhibits acetylcholinesterase Physical — coats and suffocates lice
Ovicidal (kills eggs)? Yes Partial — varies by product
Suitable age 6 months and over Varies — check individual product

 

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 — the lotion contains alcohol — so you must keep it away from naked flames, cigarettes, and other heat sources during application and while the hair is drying. Never use a hairdryer after applying it. Store the bottle below 25°C, in a cool dry place, and always keep it out of reach of children.

If you're managing other skin conditions alongside a lice infestation, it's worth exploring our skin care range for complementary products. Always check the expiry date before use, and do not use the product if the seal has been broken prior to purchase.

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 pubic lice
Active ingredient Malathion 0.5% w/v
Mechanism of action Organophosphate — inhibits acetylcholinesterase in lice
Effective against Head lice (Pediculus humanus capitis), pubic lice (Phthirus pubis), eggs (nits)
Suitable for Adults and children aged 6 months and over
Pack size 150ml
UK classification P (Pharmacy medicine)
Drug class Organophosphate insecticide / pediculicide
Preparation Topical lotion
Route of administration Topical (applied to hair and scalp)

Specifications of Derbac M Liquid 150ml

 

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

 

Derbac M Liquid is a topical lotion containing malathion 0.5% w/v, used to treat infestations of head lice (Pediculus humanus capitis) and pubic lice (Phthirus pubis). Head lice are tiny insects that live on the scalp and feed on blood. They spread easily through direct head-to-head contact, which is why outbreaks are so common in schools and nurseries. The NHS confirms that head lice are very common in children and do not indicate poor hygiene.

Derbac M Liquid kills both live lice and their eggs, helping to clear an infestation with two applications spaced seven days apart. It is available over the counter as a Pharmacy (P) medicine and does not require a prescription.

 

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

 

Before applying this treatment, read the following carefully. There are certain situations where you should not use Derbac M Liquid or should seek advice first.

Do not use Derbac M Liquid if you:

  • Are allergic to malathion or any other ingredient in the product.
  • Have broken, infected, or severely inflamed skin on the scalp.
  • Are treating an infant under 6 months of age without medical supervision.
  • Have a known sensitivity to organophosphate compounds.

Speak to your pharmacist or doctor before use if you:

  • Are pregnant or breastfeeding.
  • Have asthma — some people with asthma may be sensitive to the lotion.
  • Are using any other topical scalp treatments at the same time.

Drug interactions:

  • No clinically significant interactions are known at topical doses.
  • Avoid using other insecticide-based products on the scalp at the same time.

 

How Should You Use Derbac M Liquid?

 

Correct application is essential for the treatment to work. Follow these steps carefully to get the best result:

  1. Confirm the presence of live lice using a fine-toothed detection comb on wet hair before starting treatment.
  2. Apply Derbac M Liquid to dry hair. Part the hair into sections and apply the lotion directly to the scalp, working outwards to the ends of the hair.
  3. Rub the lotion thoroughly into the scalp and all of the hair, ensuring complete coverage.
  4. Allow the hair to dry naturally in a well-ventilated room. Do not use a hairdryer — the lotion is flammable.
  5. Leave the lotion on for at least 12 hours, or overnight if possible.
  6. Wash the hair with your normal shampoo and rinse thoroughly.
  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 all hair and scalp Two applications, 7 days apart
Pubic lice Adults Apply to affected area as directed Two applications, 7 days apart
Children under 6 months Infants Only under medical supervision As directed by a doctor

If you're also looking for products to support your child's general wellbeing during a lice outbreak, our baby and toddler range includes a variety of gentle, age-appropriate options.

 

What Are the Possible Side Effects of Derbac M Liquid?

 

Like all medicines, Derbac M Liquid can cause side effects, although not everyone experiences them. Most reactions are mild and localised to the scalp.

Common side effects:

  • Mild scalp irritation or itching after application.
  • Temporary redness of the skin at the application site.
  • A slight stinging or burning sensation on the scalp.

Less common side effects:

  • Skin rash or contact dermatitis in people with sensitive skin.
  • Eye irritation if the product accidentally contacts the eyes — rinse immediately with water.
  • Allergic reactions, including swelling, hives, or difficulty breathing — seek emergency medical help immediately if this occurs.

It's worth noting that some itching after treatment can simply be a reaction to dead lice and eggs rather than a side effect of the lotion itself. If irritation persists beyond 48 hours, consult your pharmacist.

 

How Should You Store Derbac M Liquid?

 

Proper storage keeps the product safe and effective. Follow these guidelines:

  • Store below 25°C in a cool, dry place away from direct sunlight.
  • Keep the bottle tightly closed when not in use.
  • Keep out of the reach and sight of children at all times.
  • Do not store near naked flames, heat sources, or electrical equipment — the lotion 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.

If you're managing a broader range of family health needs, our hair care collection includes products to support scalp and hair health after treatment.

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 without a prescription as an over-the-counter Pharmacy (P) medicine. Browse our full head lice treatments collection to compare available options before ordering.

How does Derbac M Liquid work in the body?

Derbac M Liquid contains malathion 0.5%, an organophosphate insecticide that inhibits the enzyme acetylcholinesterase in head lice. This disrupts normal nerve signal transmission, causing paralysis and death of both live lice and their eggs. Because it acts on the lice's nervous system, it is effective even against eggs that other treatments may miss.

How do I use Derbac M Liquid step by step?

Apply the lotion to dry hair, working it thoroughly into the scalp and all hair from root to tip. Allow the hair to dry naturally — never use a hairdryer as the product is flammable — and leave it on for at least 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 — overnight application is ideal. This extended contact time is necessary to ensure the malathion has sufficient time to kill both live lice and any viable eggs. Washing it off too early may reduce the effectiveness of the treatment.

Is Derbac M Liquid safe for children?

Yes, Derbac M Liquid is suitable for children aged 6 months and over when used as directed. For infants under 6 months, treatment should only be carried out under medical supervision. Always keep the lotion away from children's eyes, mouth, and broken skin during application.

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. While systemic absorption from topical application is considered minimal, professional guidance is recommended to ensure the treatment is appropriate for your individual circumstances. Your pharmacist can advise on suitable alternatives if needed.

What are the side effects of Derbac M Liquid?

Most people tolerate Derbac M Liquid well, but some may experience mild scalp irritation, redness, or a temporary stinging sensation after application. Less commonly, skin rash or eye irritation can occur — rinse eyes immediately with water if contact happens. If you develop signs of a serious allergic reaction such as swelling or difficulty breathing, seek emergency medical help straight away.

How many times do I need to apply Derbac M Liquid?

The standard course is two applications, with the second treatment applied exactly 7 days after the first. This two-dose approach is important because the first application kills live lice and most eggs, while the second targets any lice that may have hatched from surviving eggs in the intervening week. Skipping the second application increases the risk of re-infestation.

What are the alternatives to Derbac M Liquid?

Alternatives include dimeticone-based products such as Hedrin, which work by physically coating and suffocating lice rather than using a chemical insecticide. Permethrin-based treatments such as Lyclear are also available. The NHS recommends rotating between different active ingredients if one treatment does not appear to be working, as resistance can develop with repeated use of the same product.

Can Derbac M Liquid be used for pubic lice?

Yes, Derbac M Liquid can be used to treat pubic lice (Phthirus pubis) as well as head lice. For pubic lice, the lotion is applied to the affected area and left on for the recommended contact time before washing off. It is advisable to speak to a pharmacist or sexual health clinic for guidance on treating pubic lice, as sexual partners may also need treatment.

Why is Derbac M Liquid flammable and what precautions should I take?

Derbac M Liquid contains alcohol as part of its formulation, which makes it flammable. You must keep the treated hair away from naked flames, lit cigarettes, and other ignition sources until the hair is completely dry. Never use a hairdryer, electric straighteners, or curling tongs while the lotion is still on the hair or while the hair is drying.

Does Derbac M Liquid kill nits (eggs) as well as live lice?

Yes — malathion is both pediculicidal (kills live lice) and ovicidal (kills eggs), which is one of its key advantages over some physical treatments. However, because not all eggs may be killed by the first application, the second treatment after 7 days is essential to catch any newly hatched lice before they can mature and lay new eggs.

What should I do if Derbac M Liquid does not work?

If live lice are still present after completing both applications correctly, it is possible that the lice in your area have developed resistance to malathion. In this case, the NHS recommends switching to a product with a different active ingredient, such as a dimeticone-based lotion. Speak to your pharmacist for personalised advice on the next steps.

How long does a head lice infestation last without treatment?

Without treatment, a head lice infestation will not resolve on its own — lice will continue to breed and spread. A single female louse can lay up to 8 eggs per day, so an untreated infestation can grow quickly. Early treatment with a product like Derbac M Liquid, combined with checking and treating all household contacts, is the most effective way to clear an infestation.

Are there any latest studies or research on malathion for head lice?

Malathion has been used as a head lice treatment for several decades and remains included in NHS and BNF guidance as an effective option. Research has highlighted the emergence of resistance to some insecticides in certain regions, which is why the NHS advises rotating treatments if one product fails. Your pharmacist can advise on current local resistance patterns and the most appropriate treatment choice for your situation.

How Should You Use Derbac M Liquid?

Before you start, confirm the infestation by combing through wet hair with a fine-toothed detection comb. Treatment should only be applied when live lice are found — treating as a precaution is not recommended.

Follow these steps for correct application:

What Is the Correct Dose of Derbac M Liquid?

The amount of lotion needed will vary depending on hair length and thickness. Use enough to thoroughly wet all of the hair and scalp — this may be more than you expect for long or thick hair. Do not dilute the lotion before use.

When Is the Best Time to Use Derbac M Liquid?

Evening application is ideal, as it allows the lotion to remain on the hair overnight — giving the full 12-hour contact time needed for maximum effectiveness. Applying before bed also means the treated hair is less likely to come into contact with open flames or heat sources during the treatment period.

Make sure the room is well ventilated during application and while the hair is drying. Avoid applying the lotion near gas hobs, candles, or any other ignition source.

How Long Can You Use Derbac M Liquid For?

Derbac M Liquid is intended for short-term use only — a single course consists of two applications, seven days apart. If live lice are still present after completing both applications correctly, do not simply repeat the same treatment. Instead, speak to your pharmacist, as resistance to malathion may have developed and a different active ingredient may be needed.

Routine or preventative use is not recommended. Only treat when a confirmed infestation is present, and check all household contacts at the same time to prevent re-infestation.

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

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 limited to the area of application. It is also worth remembering that some scalp itching after treatment may simply be a response to dead lice and eggs rather than a reaction to the lotion itself.

  • Mild scalp itching or irritation after application.
  • Temporary redness or warmth of the skin on the scalp.
  • A slight stinging or burning sensation, particularly on sensitive skin.

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

A small number of people may experience more noticeable reactions, particularly those with sensitive or eczema-prone skin. If any of the following occur and do not settle within 48 hours, stop using the product and speak to your pharmacist.

  • Contact dermatitis — a red, itchy, or blistering rash on the scalp or surrounding skin.
  • Eye irritation if the lotion accidentally contacts the eyes — rinse immediately and thoroughly with clean water.
  • Dryness or flaking of the scalp following treatment.
  • Hair texture changes — some people notice temporary dryness or brittleness of the hair after use.

What Are the Serious Side Effects of Derbac M Liquid?

Serious side effects are rare with topical malathion at the concentrations used in Derbac M Liquid. However, you should be aware of the signs of a serious allergic reaction (anaphylaxis), which requires immediate emergency medical attention.

Seek emergency help immediately if you experience any of the following after using this product:

  • Swelling of the face, lips, tongue, or throat.
  • Difficulty breathing or swallowing.
  • A widespread skin rash, hives, or severe flushing.
  • Dizziness, rapid heartbeat, or feeling faint.

What Should You Do If You Experience Side Effects?

For mild reactions such as scalp irritation or redness, you can usually manage these by rinsing the area with cool water and avoiding further application until the skin has settled. Do not apply the lotion to broken or inflamed skin.

If you are concerned about a reaction, or if symptoms persist or worsen, contact your pharmacist or GP for advice. You can also report suspected side effects directly to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.

Can Derbac M Liquid Interact With Other Medicines?

No clinically significant drug interactions are known with topical malathion at the doses used in Derbac M Liquid. However, you should avoid using other insecticide-based scalp treatments at the same time, as this may increase the risk of skin irritation. If you are using any prescription scalp treatments or have a skin condition affecting the scalp, speak to your pharmacist before using this product.

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

📖 Find out more about our team of medical content authors and how we ensure the accuracy of our content with our content guidelines.

Content last updated: 31 Mar 2025

We’re a safe and
regulated UK service

Registered Pharmacy Badge

Lowest Price Guarantee

We're convinced you won't find your treatment cheaper, but if you do we'll refund the difference.

Find out more

100% discreet packaging

We're convinced you won't find your treatment cheaper, but if you do we'll refund the difference.

Find out more

Agent

Need help?
Talk to our friendly experts now

How our service works

Service Setup

Service setup

Discreet Packaging

Discreet packaging

Express Delivery

Express delivery