LDN and MCAS

LDN (Low Dose Naltrexone) is gaining attention as a promising option for people living with MCAS (Mast Cell Activation Syndrome). This guide explains what MCAS is, how LDN might help, the latest research, and practical tips for patients and pharmacy teams.

Key takeaways

• LDN and MCAS are closely linked in emerging research, with LDN showing promise for symptom control [1].
• MCAS is a complex condition that often overlaps with gut, immune, and allergy issues [2], [3].
• LDN is used “off-label” for MCAS and should only be started under specialist supervision [1].
• Managing MCAS involves more than just medication—diet, lifestyle, and stress management all play a role [3], [4].
• Courier Pharmacy offers both compounded LDN and mast cell stabilisers, such as ketotifen. These can be purchased online after completing a consultation form.

Who is this article for? How can it help? And why does it matter?

This article is for anyone living with MCAS, carers, healthcare professionals, or those curious about low-dose naltrexone or LDN as a treatment option. If you’re struggling with symptoms of mast cell activation syndrome and want new treatment options—or want to understand the science behind LDN and MCAS—you’ll find practical advice, clear explanations, and original insights here. We’ll answer the “who, how, and why” of LDN and MCAS so that you can make informed choices about your health.

What is MCAS, and why is it so complex?

Mast Cell Activation Syndrome (MCAS) is a condition where certain immune cells—mast cells—become overactive and release too many chemicals into the body [2], [3].

This can cause a wide range of symptoms—tiredness, digestive issues, skin rashes, headaches, and more [3], [4]. MCAS is tricky to diagnose and often goes unnoticed for years [2], [3].

What makes MCAS so complex?

• Symptoms can affect almost any part of the body, often changing over time [2], [3].
• It often overlaps with other conditions, like gut problems (such as SIBO), joint hypermobility (like Ehlers-Danlos syndrome), and even some forms of autoimmunity [4].
• Triggers can include foods, stress, infections, chemicals, and even temperature changes [3].

What are the symptoms and triggers of MCAS?

Symptoms vary a lot, but common ones include [2], [3]:

• Flushing or redness of the skin
• Hives or swelling
• Headaches
• Nausea, vomiting, or diarrhoea
• Tummy pain
• Wheezing or shortness of breath
• Brain fog or tiredness

These symptoms can come and go and might change over time. They can affect your skin, gut, breathing, heart, and even your brain [2], [3].

Everyone’s triggers are different, but common ones include certain foods, perfumes, stress, changes in temperature, or even just a tough day [3]. Sometimes, it’s one big trigger; other times, it’s a mix of little things that add up.

How is MCAS diagnosed and managed?

There’s no simple test. Doctors look for symptoms in different parts of your body, might try medications, and may check your blood or urine for high levels of mast cell chemicals, especially during a flare-up [2].

Management usually involves:

• Avoiding your triggers (like certain foods or stress) [3].
• Taking medicines like antihistamines or mast cell stabilisers (for example, ketotifen or Zaditen, available at Courier Pharmacy) [3].
• Carrying an adrenaline injector (like an EpiPen) if you’re at risk of severe reactions [3].

Other helpful steps include keeping a diary of your symptoms and triggers and working closely with a knowledgeable healthcare professional.

Why is MCAS tricky to spot?

• Symptoms can affect nearly any part of the body, often changing over time.
• It frequently overlaps with gut issues (like SIBO), joint hypermobility, and even autoimmune problems [4].
• Triggers include foods, stress, infections, chemicals, and temperature changes [3].

How does LDN fit into the picture?

Low Dose Naltrexone (LDN) is a medicine usually taken in small doses (1–5mg). It’s not officially licensed for MCAS, but some doctors prescribe it “off-label” because it may help calm the immune system and reduce inflammation [1].

What is Low Dose Naltrexone (LDN)?

Low Dose Naltrexone (LDN) is a medication that’s getting a lot of interest for its potential to help with a range of long-term health problems, including chronic pain, immune issues, and conditions like Mast Cell Activation Syndrome (MCAS) [1].

But to really understand LDN, it helps to know where it started and how it works in the body.

Original use: treating addiction at higher doses

Naltrexone was first developed to help people struggling with opioid or alcohol addiction [6].

At much higher doses (usually around 50mg or more), it acts as a strong “blocker.” It completely covers the opioid receptors in the brain—these are like locks that your body’s natural painkillers, or endorphins, and drugs like morphine fit into [6].

When someone takes a high dose of naltrexone, it blocks these locks so that opioid drugs can’t get in, meaning they won’t have any effect. This helps people avoid relapse and lose the “reward” feeling from these drugs [6].

What’s different about Low Dose Naltrexone?

LDN is the same medicine, but used in much smaller amounts—usually between 1mg and 4.5mg. At this low dose, it works in a totally different way. Instead of completely blocking the opioid receptors all day, LDN only blocks them for a short time [6].

How does LDN work in the body?

When you take LDN, it temporarily sits in the opioid receptors (the “locks”), blocking your body’s natural painkillers (endorphins) from getting in. Your body quickly notices this and responds by making more endorphins to try to get around the block. Once the LDN wears off, you’re left with extra endorphins in your system. These natural chemicals are known to help with pain relief, boost mood, and can even support your immune system [6].

So, in simple terms:

• High-dose naltrexone: Completely blocks opioid receptors all day, stopping both drugs and natural painkillers from working. Used for addiction treatment.
• Low Dose Naltrexone: Briefly blocks receptors, then lets them go, which encourages your body to make more of its own natural painkillers. Used “off-label” for conditions like chronic pain, autoimmune diseases, and MCAS.

What is LDN used for today?

Doctors are now exploring LDN for a variety of conditions where the immune system is overactive, or where people have ongoing pain or inflammation [1],[6]. This includes things like MCAS, fibromyalgia, Crohn’s disease, and multiple sclerosis.

It’s not officially approved for these uses, so it’s called “off-label,” but many people find it helpful, often with fewer side effects than other medicines.

How does LDN work?

Low-dose naltrexone gently “nudges” both your immune and nervous systems, rather than just blocking opioid receptors. At low doses, LDN acts on special brain cells (glial cells) and toll-like receptors, helping to quiet inflammation.

LDN briefly blocks opioid receptors, prompting your body to make more of its own natural painkillers (endorphins). The unique “shape” of LDN’s molecules means it can target different pathways at once, explaining its wide-ranging effects [6].

When you take LDN at bedtime, it temporarily blocks your body’s opioid receptors. The brain notices this and responds by making more endorphins and other “feel-good” chemicals. When LDN wears off, your body is left with a higher supply of these natural painkillers, which can help with pain, mood, and even immune regulation [6].

Why is LDN called “pleiotropic”?

“Pleiotropic” means “having many different effects.” LDN isn’t just about pain relief—it’s being studied for its impact on mood, immune balance, inflammation, and even cell growth. Its broad action is why researchers are excited about its potential for so many different conditions [6].

Chirality and dual action

Low-dose naltrexone contains two mirror-image forms (like left and right hands) called “isomers.” One form (levo-naltrexone) helps boost endorphins and regulate the immune system [6].

The other (dextro-naltrexone) helps calm inflammation by blocking specific immune sensors in the brain. At low doses, though, LDN also calms special immune cells in the brain (microglia) by blocking toll-like receptor 4 (TLR4). This helps reduce inflammation, pain, and “brain fog,” especially in chronic conditions  [6].

Together, these forms allow LDN to support both pain relief and inflammation control [6].

What does the research say about LDN and MCAS?

The first published case showing how well low-dose naltrexone works for MCAS involved a patient who also had POTS (a condition where your heart races when you stand up) and SIBO (a gut problem with too many bacteria).

Along with antibiotics for her gut, she was given LDN and a special immune treatment called intravenous immunoglobulin (IVIg). The results were impressive: she had more than 40 tough symptoms from all three conditions, but after treatment, many of these symptoms got much better and stayed that way [7].

While IVIg is already used for some nerve and immune problems, there isn’t much research on how it helps with POTS or MCAS. In this patient’s story, IVIg and an antibiotic called rifaximin helped, but the real breakthrough came when she increased her dose of LDN from 2mg to 4.5mg—after that, her symptoms improved completely [7].

MCAS needs more than medicine

Because MCAS involves numerous chemicals and cell signals, no single medicine can fix everything. Doctors usually start by helping people avoid their triggers, and then might prescribe antihistamines, mast cell stabilisers, like ketotifen, vitamin C, vitamin D, or montelukast [3]. But lately, more doctors are adding LDN to this mix and are seeing even better results for their patients [1],[7].

While large-scale studies are still lacking, case reports and small trials suggest low-dose naltrexone can help people with MCAS, particularly if they also have gut symptoms.

For example, in a published case, a woman with MCAS, SIBO, and joint hypermobility saw significant improvements in her gut symptoms and overall well-being after starting LDN alongside other treatments [1].

What else helps with MCAS?

Managing MCAS usually involves a combination of approaches [3] :

• Antihistamines and mast cell stabilisers (like ketotifen) to calm symptoms.
• Dietary changes to avoid trigger foods.
• Supplements such as vitamin C and quercetin, which may help stabilise mast cells.
• Stress management and mental health support, since stress can worsen symptoms.

Is LDN safe for MCAS?

Low-dose naltrexone is generally well-tolerated. Side effects are usually mild, such as sleep changes or vivid dreams. However, because it’s “off-label” for MCAS, it should only be started under the care of a doctor who understands your health history and can monitor your progress [5].

Practical tips for living with MCAS (and using LDN)

• Work with a specialist: MCAS is complex—find a doctor or pharmacist who understands the condition, such as the specialist LDN team at Courier Pharmacy
• Keep a symptom diary: Track your triggers, symptoms, and responses to treatments like LDN.
• Be patient: Improvements with LDN can take weeks or months.
• Don’t go it alone: Join support groups or online communities for MCAS and LDN.
• Ask about compounding: Low-dose naltrexone or LDN needs to be specially compounded by specialist pharmacies. To simplify things, you can get your prescriptions and compounded LDN from Courier Pharmacy online after completing the online consultation form.

Frequently asked questions (FAQs)

What is MCAS?

Mast Cell Activation Syndrome (MCAS) is a condition where immune cells called mast cells become overactive, releasing chemicals that cause a range of symptoms from rashes to tummy pain.

What is LDN, and how does it help MCAS?

LDN is a low dose of the medicine naltrexone. It’s thought to calm the immune system and reduce inflammation, which can help manage MCAS symptoms.

Is LDN safe for everyone?

LDN is generally safe, but it should only be started under the care of a knowledgeable healthcare professional.

How long does it take for LDN to work in MCAS?

Some people notice improvements within weeks, but it can take several months for the full effects to take hold.

Can I get LDN from Courier Pharmacy?

Yes, Courier Pharmacy offers LDN with a prescription and expert support for people with MCAS after completing an online consultation form.

Summary

If you have MCAS and standard treatments aren’t giving relief, LDN may be worth discussing with your doctor.

While it’s not a cure, it could help reduce symptom flares and improve quality of life, especially for those with gut symptoms. Always seek expert advice before starting new treatments.

This information is for general guidance only. For medical advice, please consult your doctor or healthcare provider.

References:

1. Quinn, A.M. (2023) ‘Complex Presentations, Identification and Treatment of Mast Cell Activation Syndrome and Associated Conditions: A Case Report’, Cureus, 15(9), e44353. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC10519234/ (Accessed: 2 August 2025).

2. Molderings, G.J., Homann, J., Brettner, S., Raithel, M. and Frieling, T., 2014. Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options. Deutsche medizinische Wochenschrift (1946), 139(30), pp.1523-34. Available at: https://pubmed.ncbi.nlm.nih.gov/25099295/ (Accessed: 2 August 2025).

3. Courier Pharmacy (2025) What is mast cell activation syndrome? [Online] Available at: https://courierpharmacy.co.uk/what-is-mast-cell-activation-syndrome/ (Accessed: 3 August 2025).

4. Courier Pharmacy (2025) Mast Cell Activation Syndrome and gastrointestinal symptoms. [Online] Courier Pharmacy. Available at: https://courierpharmacy.co.uk/mast-cell-activation-syndrome-and-gastrointestinal-symptoms/ (Accessed: 4 August 2025).

5. Courier Pharmacy (2025) Low dose naltrexone (LDN) safety: Is it safe to use? [Online] Courier Pharmacy. Available at: https://courierpharmacy.co.uk/is-ldn-safe/ (Accessed: 4 August 2025).

6. Courier Pharmacy (2025) How low dose naltrexone (LDN) works in the body. [Online] Courier Pharmacy. Available at: https://courierpharmacy.co.uk/how-does-ldn-work/ (Accessed: 4 August 2025).

7. Weinstock, L.B., Brook, J.B., Myers, T.L. and Goodman, B., 2018. Successful treatment of postural orthostatic tachycardia and mast cell activation syndromes using naltrexone, immunoglobulin and antibiotic treatment. Case Reports, 2018, pp.bcr-2017