Medical cannabis treatments for mast cell activation syndrome (MCAS)

Mast cell activation syndrome (MCAS) is a complex immunological condition where abnormal mast cells release chemical mediators that trigger widespread symptoms throughout the body. Medical cannabis may help eligible patients manage associated symptoms, including pain, anxiety and sleep disruption.

What is mast cell activation syndrome (MCAS)?

Mast cell activation syndrome (MCAS) is a rare immunological condition where mast cells become overly reactive, causing allergy-related symptoms that can affect multiple areas of the body.

While we still don’t know a huge amount about the condition, MCAS is thought to be brought on when mast cells function abnormally. But what exactly are mast cells? 

Mast cells are an important part of the immune system that help us all fight against infections. Produced in the bone marrow, these cells kick into action when they detect a potential allergen, releasing histamine and several other chemical mediators to combat the ‘threat’. 

It’s the release of these chemicals that then causes the whole host of symptoms associated with having an allergic reaction, everything from having a blocked or runny nose to the skin becoming itchy and swollen.

When the function of these mast cells becomes abnormal, this can result in the symptoms of a specific mast cell disorder, such as MCAS. 

Are there different types of mast cell disorders? 

Yes, there are two main types of mast cell disorders: mastocytosis and MCAS. 

Mastocytosis occurs when the body produces too many mast cells, causing them to build up in the skin, bone marrow or organs around the body.

MCAS is slightly different. MCAS patients typically have a normal number of mast cells, but those cells release chemical mediators inappropriately, resulting in various symptoms.

Who does MCAS affect in the UK?

In the UK, you may have an increased risk of MCAS if you: 

• are a woman (65 to 70% of MCAS patients are women)

• have been diagnosed with a connective tissue disease, an autoimmune disorder or inflammatory condition

• have a history of allergies, asthma or eczema 

• have a family member already diagnosed with a mast cell disorder

Environmental factors like recurrent viral infections may also play a role, with some research suggesting MCAS symptoms can be triggered or worsened by infections like COVID-19.

What conditions commonly co-occur with MCAS?

MCAS is particularly difficult to diagnose due to its symptoms overlapping with several other conditions. This is partly because the condition commonly co-occurs alongside several other conditions, including: 

• fibromyalgia

• chronic fatigue syndrome 

• irritable bowel syndrome

• sickle cell disease

• endometriosis

• migraines

• depression and anxiety disorders

Having this symptom overlap often means many patients are misdiagnosed or treated for individual symptoms before MCAS is identified as the underlying cause.

In fact, certain studies have indicated that it can take some patients up to 30 years to get a formal MCAS diagnosis. 

How does MCAS interact with co-occurring conditions like hEDS and PoTS?

MCAS is often associated as part of a “triad” alongside certain other conditions like Postural Orthostatic Tachycardia Syndrome (PoTS) and hypermobile Ehlers-Danlos Syndrome (hEDS). 

PoTS and hEDS were already known to commonly co-occur together, but researchers have since found that approximately 66% of patients report symptoms consistent with MCAS too. 

While researchers are still working to understand the link between these three conditions, some studies suggest that mast cell mediators may contribute to the overlapping symptoms they each cause.

What symptoms does mast cell activation syndrome cause?

Since mast cells are found throughout the body, MCAS-associated symptoms typically affect multiple areas at the same time. They also vary widely from patient to patient, so there’s no hard and fast rule about which symptoms you’ll develop. 

That said, over 50% of MCAS patients report experiencing symptoms like: 

• fatigue

• widespread body pain

• itching, hives or nettle rash (urticaria)

• skin swelling that moves around the body

• chills and tingling sensations

• headache

• breathlessness or wheezing

• feeling faint or fainting

• eye irritation

In addition to these symptoms, MCAS may also lead to the development of several others. This includes: 

• abdominal cramps and diarrhoea

• red skin (flushing)

• blocked nose

• rapid heart rate (tachycardia)

• variable blood pressure

• sleep disturbances

• anaphylaxis (in severe cases)

If you’re experiencing any of these symptoms, make sure to speak to a medical professional for tailored advice and support.

What treatments are currently available for mast cell activation syndrome?

The treatments available for MCAS are typically built around two main goals: blocking the effects of histamine and stabilising the mast cells. 

Most MCAS patients will be given a treatment plan that involves a combination of approaches to help both manage and reduce the onset of associated symptoms. 

Here's a quick overview of the main treatment options available for MCAS:

 

 

For patients who experience severe reactions or anaphylaxis, an emergency adrenaline auto-injector may also be prescribed.

Many MCAS patients find that managing the condition requires a layered approach, trying different treatments to help control individual symptoms. 

To learn more about the treatments that have helped our existing MCAS patients, take a look at our patient stories.

Can medical cannabis treatment help with mast cell activation syndrome symptoms?

Having a medical cannabis prescription for MCAS may help to alleviate certain symptoms of the condition, particularly in terms of the chronic pain, anxiety and sleep disruption it can cause.

That said, medical cannabis isn't a cure for MCAS, and it should never replace targeted conventional medications like antihistamines or mast cell stabilisers. 

What it may help to do is ease some of the day-to-day symptoms that can persist alongside conventional treatments. This may include symptoms like 

• persistent or widespread pain

• anxiety and low mood

• sleep disturbances

• general fatigue

How does medical cannabis work for MCAS? 

Medical cannabis contains two main active compounds, known as tetrahydrocannabinol (THC) and cannabidiol (CBD).

• THC is psychoactive and is associated with offering pain relief, improved sleep and reduced anxiety

• CBD is non-intoxicating and is better known for its potential anti-inflammatory effects, alongside its ability to support mood, sleep and overall wellbeing

For MCAS patients, finding the right balance between THC and CBD is particularly important, due to how reactive mast cells can be when new substances are introduced. This is why taking a personalised, clinician-led approach is so critical.

How does the endocannabinoid system relate to mast cell activation syndrome?

The endocannabinoid system (ECS) is a complex cell-signalling network that helps regulate many of our body’s processes. 

The system relies on two main receptors, CB1 and CB2. 

• CB1 receptors are mostly found in the brain and central nervous system

• CB2 receptors sit largely within immune cells

• Both receptors respond to the cannabinoids contained in medical cannabis, such as THC and CBD

What makes the ECS particularly relevant to MCAS is that mast cells themselves have CB1 and CB2 receptors on their surface. This gives cannabinoids a potential direct line of communication with the abnormal mast cells associated with MCAS, potentially influencing whether they release the chemical mediators they contain. 

While research is still ongoing, preclinical studies suggest that cannabinoid receptor activation may help to calm overactive mast cells, reducing the release of histamine and other inflammatory chemicals. 

But the picture isn't entirely straightforward. 

Some research suggests certain cannabinoids may have variable effects on mast cells depending on the dose and delivery method. 

That's why MCAS patients typically benefit from starting treatment at a very low dose, adjusting it slowly under clinical guidance.

What does research say about medical cannabis and MCAS?

With MCAS being such a poorly understood condition, it’ll come as no surprise to hear that specific research into medical cannabis as a potential treatment for the condition remains very limited. 

That said, a growing body of evidence has explored how cannabinoids may help with the related symptoms and co-occurring conditions that many MCAS patients experience.

Here’s a quick overview of what the key studies have found over recent years: 

 

 

The results from our UK medical cannabis 2025 patient survey are also worth mentioning, as 97% of respondents reported experiencing an improved quality of life from taking prescribed medical cannabis. 

Am I eligible for UK medical cannabis treatment for mast cell activation syndrome?

Following the UK government’s decision to update the law in November 2018, MCAS is recognised as one of the many conditions that qualify for prescribed medical cannabis treatment. 

However, it’s important to note that eligibility is always assessed on an individual basis. 

Here's a quick overview of what you'll need to meet our MCAS eligibility criteria at Releaf:

 

How is Releaf medical cannabis prescribed for mast cell activation syndrome?

To find out if you qualify for an MCAS medical cannabis prescription, use our medical cannabis eligibility checker. It's free, takes around 30 seconds to complete and may be your first step towards finding effective relief.

If you’re deemed eligible, you’ll be offered the opportunity to book an initial consultation with a member of our world-class clinical team. 

They will then discuss your condition, symptoms and medical history with you in more detail to see whether medical cannabis may be suitable for your condition. 

Our knowledge hub also contains a ton of useful information about how our prescription process works, including a full step-by-step breakdown. 

FAQs on medical cannabis for mast cell activation syndrome

With MCAS being a relatively poorly understood condition, we’re here to help answer any questions you might have. Here are some of the questions we get asked about most often. 

Can medical cannabis trigger a mast cell reaction in MCAS?

In rare cases, yes. Since MCAS can be brought on by certain triggers, some patients may react to ingredients contained within medical cannabis products. That’s why adopting a careful, clinician-led approach is so important. 

Can medical cannabis help with the anxiety related to MCAS?

Yes, some patients report experiencing improvements in anxiety when taking prescribed medical cannabis. 

While individual responses can vary, medical cannabis treatments can also be tailored to help with specific symptoms, such as anxiety.

Can medical cannabis help with MCAS-related cognitive fog?

There is currently limited research on medical cannabis and cognitive fog specifically. 

However, some MCAS patients report improvements in mental clarity when their underlying symptoms like pain, anxiety and poor sleep are better managed. 

How is medical cannabis monitored for MCAS patients at Releaf?

If you're deemed eligible for a medical cannabis prescription, your consultant will typically start you on a very low dose and review your progress regularly at each of your follow-up appointments. 

Given how reactive mast cells can be in terms of triggers, adopting a cautious approach is very important. Your dose will then be adjusted carefully over time, depending on how your symptoms respond.

Releaf - let's rethink healthcare