Introduction

Migraines are recurrent neurological disorders often associated with aura, nausea, photophobia, and phonophobia. Such headaches are detrimental to a person’s quality of life and work, leading to decreased work output and increased health expenditure.

As a crucial part of the central nervous system, the endocannabinoid system (ECS) modulates different functions, including pain, inflammation and neuroprotection. The ECS includes the endocannabinoids, their receptors, and metabolic enzymes, which promote a sense of internal equilibrium. Emerging research suggests that ECG dysfunction may contribute to migraine pathology. A deeper understanding of this relationship could pave the way for novel therapeutic approaches to migraine management. 

Overview of the Endocannabinoid System

The endocannabinoid system (ECS) comprises a complex cell-signalling system, performing crucial functions such as maintenance of homeostasis in the body. The ECS comprises 3 main components: endocannabinoids, receptors and enzymes

Endocannabinoids

• The anandamide (AEA) and 2-arachidonoyglycerol (2-AG) are lipid-based neurotransmitters produced by the body on demand. These molecules interact with the cannabinoid receptors (CB1 and CB2) to regulate physiological processes

Receptors

• CB1 receptors: they are commonly highly concentrated in the brain and the central nervous system and play a prominent role in influencing neural signalling, mood, appetite, pain perception and other similar processes
• CB2 receptors: they are found in the immune system and peripheral tissues and play a role in inflammation and immune responses

Enzymes

3. Fatty acid amide hydrolase (FAAH) and monoacylglycerol lipase (MAGL) degrade the endocannabinoids AEA and 2-AG, ensuring their activity is thoroughly regulated¹

By playing a role in the aforementioned physiological functions, the ECS thus influences pain modulation, neural signalling (enhancing of the synaptic plasticity and neuroprotective capabilities), and vascular regulation (regulation of blood flow and cardiovascular health).² Understanding the physiological perspective of the ECS, provides insights for therapeutic potential and disease management in conditions such as chronic pain, migraines, mood disorders and neurodegeneration.

Migraine pathophysiology

Migraines are extremely complex and debilitating neurological disorders, characterised by recurring episodes of severe headaches, often with sensory disturbances. An understanding of migraine pathophysiology is crucial for diagnosing and treating the condition.

A key feature of migraine is the experience of neurological hypersensitivity, which refers to the heightened excitability of the central nervous system. This process triggers the activation of the trigemino-vascular system, a critical pathway in migraine pathophysiology, causing an abnormal processing of sensory inputs. This activation further results in the release of inflammatory neuropeptides, such as the Calcitonin gene-related peptide (CGRP), responsible for throbbing pain experience and vasodilation.³

Another hallmark event in the physiology of migraine is cortical spreading depression (CSD), a wave of neuronal depolarisation that is followed by inhibition across the cerebral cortex. CSD further activates the trigeminal neurones, promoting inflammation and sensitisation of cranial pathways. Several other neurotransmitters, such as serotonin (5-HT), regulate the vascular tone in pain pathways, and decreased serotonin levels can trigger migraines. Glutamate, an excitatory neurotransmitter, enhances neuronal hyperactivity and facilitates cortical spreading depression.⁴

These highly interconnected processes paint a picture of the complexities in migraine physiology and open up an avenue of therapeutic targets for intervention.

Associations between ECS and migraine

Recent research highlights the role of ECS dysfunction in migraine pathophysiology, providing new avenues for intervention.

Various clinical studies have shown that individuals with migraines often present with low levels of anandamide (AEA), an endocannabinoid crucial for pain modulation and neuroprotection. Low levels of AEA impair the endocannabinoid system’s ability to regulate pain and inflammation, thereby exacerbating migraine symptoms and pain. Moreover, genetic polymorphisms in ECS-related genes, such as those responsible for breaking down AEA and encoding the enzyme fatty acid amide hydrolase (FAAH), are associated with higher susceptibility to migraines.⁵

Pre-clinical studies highlight the therapeutic potential of ECS modulation in migraine management. Inhibiting FAAH increases AEA levels, reducing migraine-associated pain and inflammation.

The role of CGRP in triggering cranial vasodilation and neurogenic inflammation results in the amplification of pain perception and makes this a critical target for therapeutic intervention. Currently explored interventions include CGRP receptor antagonists and monoclonal antibodies, which show effectiveness in triggering migraine frequency and severity.

The endocannabinoid system suppresses the release of CGTP by interacting with CB1 and CB2 receptors on trigeminal neurones and immune cells, thus modulating downstream effects. This helps alleviate vasodilation, decrease inflammatory mediators and stabilise vascular tone. The ECS also exerts anti-inflammatory effects, mitigating the release of pro-inflammatory cytokines to sensitise cranial pain pathways.⁶

The ECS plays a role in maintaining homeostasis within the brain, affecting regions such as the hypothalamus and brainstem. These regions regulate pain perception, autonomic responses and circadian rhythms, often disrupted in migraine pathophysiology. The hypothalamus, responsible for controlling appetite, stress and circadian rhythms, is affected by migraine attacks, leading to hormonal fluctuations and irregular sleep patterns. Dysregulation of ECS activity in the hypothalamus may be addressed by AEA acting on CB1 receptors to bring back homeostasis. Similarly, brainstem centres such as the periaqueductal Gray and the trigeminal nucleus caudalis are critical in pain processing and modulation. ECS dysregulation weakens the ability of these areas to suppress pain, leading to chronic pain and migraines. The ECS also influences autonomic responses such as heart rate, blood pressure and gastrointestinal motility, which alter during migraine episodes.⁷

Therapeutic potential of targeting the ECS in migraines

Cannabinoids, both Phytocannabinoids (those derived from the cannabis plant) and synthetic cannabinoids, exhibit therapeutic effects to alleviate migraine symptoms by interacting with the ECS.

Phytocannabinoids 

Such as tetrahydrocannabinol (THC) and cannabidiol (CBD), demonstrate unique mechanisms of action within pathways in the central nervous system. 

• THC: a partial agonist of CB1 and CB2 receptors, influences these pathways by reducing the release of neurotransmitters such as glutamate and calcitonin gene-related peptide (CGRP). THC also reduces cortical spreading depression and promotes regular vasodilation. However, its psychoactive side effects raise concerns about dependence and widespread use as a therapeutic agent⁸
• CBD: unlike THC, CBD lacks psychoactive effects and exerts anti-inflammatory, analgesic and neuroprotective effects. CBD indirectly supports ECS function by inhibiting the breakdown of AEA, enhancing its availability. CBD also interacts with serotonin receptors, thereby reducing migraine-associated pain and nausea

Synthetic cannabinoids and ECS modulators

They provide alternatives in migraine management.

• FAAH inhibitors: increase endogenous AEA levels, enhancing the pain-relieving and anti-inflammatory properties without any psychoactive side effects
• MAGL inhibitors: boost 2-arachidonoylglycerol (2-AG) levels, regulating neurotransmitter release and providing precise management of migraine⁹ 
• CGRP antagonists and monoclonal antibodies: are not directly related to the ECS but cause suppression and inflammation reduction and offer targeted relief, focusing on modulating migraine and pain specific pathways

Further clinical trials are needed to better understand the molecular mechanisms underlying cannabinoids and ECS modulators as innovative treatment options.

Limitations and controversies

While targeting the ECS provides many therapeutic opportunities for migraine, there remain many challenges in research.^10,11

Complexity of the endocannabinoid system

The ECS regulates many physiological processes, such as pain, mood, appetite and immune responses. The role of ECS in systems beyond migraines creates challenges in developing targeted treatments without side effects; for example, modulated ECS may affect a patient’s mood and cognition, further complicating their clinical condition.

Regulatory barriers

Legal restrictions on cannabinoid use vary globally, limiting research and clinical applications. Researchers and clinicians also raise ethical concerns pertaining to dosage levels as well as widespread unregulated access to such cannabinoids.

Need for more robust clinical trials

More large-scale, evidence-based therapies supporting the use of cannabinoids in migraine treatment are needed, with standardised protocols to establish safety, efficacy and dosing. Personalised treatment approaches must also be explored to account for individual variations in ECS function and take.

Summary

The endocannabinoid system is a crucial modulator of the migraine pathophysiology and is involved in pain perception, inflammation, and vascular regulation. Dysfunction in the ECS cause disturbances resulting in neurological hypersensitivity and pain amplification commonly associated with migraines, making it an attractive target for therapeutic intervention.

While the implications for clinical practice are significant, since ECS-targeted therapies show promise in the treatment of migraine, more comprehensive research is required to fully utilise the potential of the ECS in migraine management. More substantial clinical trials, standardised protocols, and a greater understanding of mechanisms underlying the ECS will be critical to fully unlocking its therapeutic potential.