Hi Friend
At Mend Clinic, we are always looking for treatments that go beyond simply managing symptoms and instead address the underlying mechanisms driving chronic illness. One of the most exciting tools in our clinical toolkit right now is Low Dose Naltrexone — or LDN — and I wanted to take some time to explain what it is, how it works, and why I have been increasingly recommending it for patients with Mast Cell Activation Syndrome.
First, What Is Naltrexone?
Naltrexone has actually been around for decades. At its standard dose of 50mg, it has been used for many years in addiction medicine to block the effects of opioids and alcohol. But something interesting was discovered — that at a much, much lower dose, typically between 0.5mg and 4.5mg daily, it appears to have a completely different and remarkable set of effects on the immune system and nervous system. This low-dose application is what we call Low Dose Naltrexone, or LDN.
It is important to note that LDN is used off-licence in the UK, meaning it is not yet officially approved for the conditions we use it for. However, the growing body of clinical evidence and patient experience supporting its use is significant, and it is being used by an increasing number of specialist clinicians both here and internationally.
How Does LDN Actually Work?
This is where it gets fascinating. LDN works through two main mechanisms:
1. The Endorphin Rebound Effect
When you take a low dose of naltrexone — typically at night — it briefly and temporarily blocks your opioid receptors for a few hours. Your brain senses this blockade and responds by producing a surge of natural endorphins to compensate. By the time you wake up in the morning, the naltrexone has worn off and your endorphin levels are significantly elevated compared to baseline. These endorphins play a crucial role in regulating immune function, modulating pain, and supporting mood and wellbeing. This is why we always advise taking LDN at night on an empty stomach — to maximise this rebound effect.
2. Microglial Modulation and Neuroinflammation
The brain contains immune cells called microglia. In conditions like MCAS, fibromyalgia, ME/CFS, and chronic pain, these microglial cells become chronically activated and drive a state of persistent neuroinflammation — essentially, the brain's own immune system is stuck in an "on" position. LDN appears to directly calm this microglial activation, reducing neuroinflammation and helping to break the cycle of central sensitisation that makes pain feel amplified and overwhelming. This is a fundamentally different mechanism to anything conventional pain management offers, and it is one of the reasons LDN can reach symptoms that other treatments simply cannot touch.
Why Is LDN Particularly Relevant in MCAS?
Mast Cell Activation Syndrome is, at its core, a condition of immune dysregulation — mast cells firing inappropriately and flooding the body with inflammatory mediators. But MCAS does not just affect the body. The mast cells that line the gut, the nervous system, and the brain are also involved, contributing to brain fog, fatigue, anxiety, pain amplification, and autonomic dysfunction.
This is where LDN becomes particularly powerful in the MCAS context:
Neuroinflammation is a significant driver of the brain fog, cognitive difficulties, and fatigue that so many of our patients describe. By calming microglial activation, LDN directly targets this mechanism in a way that antihistamines alone cannot.
Central sensitisation — where the nervous system becomes hypersensitised to pain signals — is common in MCAS patients, particularly those with co-existing fibromyalgia or hypermobility. LDN helps to dial down this hypersensitivity.
Autonomic nervous system dysregulation — the persistent fight-or-flight state that drives so many MCAS symptoms — appears to be positively influenced by LDN through its effects on endorphin levels and immune modulation.
Fatigue and post-exertional malaise — for patients who also have features of ME/CFS alongside MCAS, LDN has shown particular promise in reducing the severity and frequency of energy crashes.
Mast cell stabilisation — there is emerging evidence to suggest that LDN may have a direct mast cell stabilising effect in addition to its neurological benefits, making it a genuinely complementary addition to the antihistamine and ketotifen framework we use as our first-line MCAS treatment.
How We Use LDN at Mend Clinic
We introduce LDN carefully and gradually. Starting at a very low dose — typically 0.5mg — and titrating up slowly over several weeks is essential to minimise side effects, the most common of which are vivid dreams and mild sleep disturbance in the first few weeks of treatment. These almost always settle with time.
We typically start with capsules for the first month to allow precise dose titration, before transitioning to a liquid formulation for those who require more flexibility in their dosing. LDN is sourced through specialist compounding pharmacies and costs approximately £35 per month — making it one of the most cost-effective treatments available for these complex chronic conditions.
One important safety point — LDN cannot be taken alongside opioid-based medications such as codeine, tramadol, or morphine, as it will block their effect and can cause withdrawal. This is something we always review carefully before prescribing.
LDN typically takes four to six weeks to reach its full therapeutic effect, so patience is important. We ask our patients to continue with their existing MCAS medication regime whilst LDN builds up, and we monitor progress carefully through our weekly check-in system.
Why the Type of LDN You Take Matters — A Lot
This is something I feel very strongly about and do not think gets spoken about enough, particularly in the MCAS community.
Not all LDN is created equal. If you have ever looked into sourcing LDN independently, you may have come across preparations that are brightly coloured — vivid pinks, blues, yellows — or that contain a long list of ingredients including bulking agents, fillers, preservatives, sweeteners, and artificial flavourings. For most people, these additives are unremarkable. But for a patient with MCAS, whose mast cells are primed to react to almost anything foreign or chemical, these ingredients can be a significant and entirely avoidable source of reactions and flares.
I have seen patients who have tried LDN elsewhere and reported feeling worse — experiencing increased symptoms, flushing, gut reactions, or heightened sensitivity — and in a number of cases I believe the culprit was not the LDN itself but the additional ingredients in the preparation they were taking.
This is why at Mend Clinic we are extremely particular about the LDN formulation we prescribe. The liquid preparation we use contains just two ingredients — naltrexone and olive oil. Nothing else. No colours, no fillers, no bulking agents, no preservatives, no sweeteners. Just the active ingredient in a clean, simple, well-tolerated base.
For our MCAS patients, this is not a minor detail — it is a clinically important distinction. The whole point of treatment is to calm mast cell reactivity, and introducing a preparation full of potential chemical triggers is working directly against that goal. A clean formulation gives the LDN the best possible chance of doing its job without adding fuel to the fire.
What Have I Seen in Practice?
I want to be honest that LDN is not a cure, and it does not work for everyone. But what I have seen in my MCAS patients has genuinely impressed me.
The improvements I have observed most consistently are in fatigue and energy levels, cognitive function and brain fog, pain — particularly the widespread, hard-to-treat pain that does not respond well to conventional analgesia — sleep quality, and overall sense of wellbeing and resilience to flares.
Several of my patients who had reached a plateau on antihistamines and ketotifen alone have experienced a meaningful step change in their quality of life after introducing LDN. For some, it has been the piece of the puzzle that allowed them to return to work, reconnect with family life, or simply get through a day without ending up in bed.
That, for me, is what makes it worth talking about.
Is LDN Right for You?
If you are already on our MCAS programme and feel your fatigue, brain fog, or pain are not sufficiently controlled on your current regime, LDN may well be the next step in your treatment plan. Please do raise this at your next consultation or via your dashboard messaging, and we can discuss whether it is appropriate for you.
If you are not yet on our programme and recognise yourself in what you have read today, please do get in touch. The combination of mast cell-directed treatment and LDN is offering real hope to people who have spent years being told nothing is wrong.
You can book a initial consultation here. You will get sent a very detailed intake form prior to your important which will be reviewed so we know you very well before we have even met, this has really help make the appts more productive.
Stay Well
Dr Ahmed
The information in this newsletter is intended for general educational purposes only and does not constitute individual medical advice. LDN is a prescription medication and must only be started under the supervision of a qualified clinician. If you think LDN may be appropriate for you, please book a consultation before taking any action.
