On this page you can find a summary of the last news and researches from scientist publications sources. Most of these reasearches are pre-clinical conclusions on small groups of people or observations on animals, this article or our products are absolutely not intended to diagnose, treat, cure or prevent any disease. Consult your professional healthcare for any specific condition.

What is Cough and How Does it Occur?

Cough is known as the reflex that leads to the expulsion of the content of the respiratory tract, including mucus, irritants, dust, liquids, or foods. This reflex prevents the entry of harmful material inside the lungs, which can cause severe complications, including lung inflammation, pneumonia, irritation, or sudden shortness of breath. Cough is the main reason for presentation in clinics, accounting for up to 40% of daily clinic visits.

Under normal conditions, cough acts as a protective mechanism. However, in some conditions, it might become frequent, severe, and harmful to the airway. This type of cough needs medical attention because of the presence of an underlying medical problem. Cough is normally initiated by the irritation of cough receptors inside the trachea by foreign bodies. This irritation leads to the activation of these receptors, leading to activation of the cough center in the brain, which sends an impulse to the respiratory muscles and the muscles of the pharynx to contract to expel the foreign material. 

Therefore, the cough reflex is mediated by the following pathways:

  1. Afferent pathway: This consists of the nerve fibers that are located in the epithelial covering of the upper airways (trachea, pharynx, and larynx).
  2. Central pathway (cough center): The impulse that is generated by the nerve fibers in the upper airways travel to the cough center in the brain in a region called the medulla.
  3. Efferent pathway: The cough center sends impulses that travel through other nervous tracts to stimulate the contraction of the diaphragm, the abdominal wall muscles, and the respiratory muscles. 

Cough can be classified into acute and chronic

Acute cough occurs suddenly within a period of 2 days, with no prior medical illness. However, chronic cough is defined as the presence of cough for more than 2 weeks. It is often associated with chronic respiratory conditions, particularly chronic obstructive pulmonary disease (COPD).

Pathways of Cough

The Endocannabinoid System and Cough Reflex

Many phytocannabinoids exist in the hemp plant, including tetrahydrocannabinol (THC) and CBD. However, CBD has gained much attention for its therapeutic roles in various medical problems, including pain, inflammation, and many others. Cannabinoids don’t exist in marijuana alone; however, they also exist in our body in the form of endocannabinoids. These endocannabinoids interact with target receptors known as cannabinoid receptors type 1 (CB1) and type 2 (CB2). The system that regulates the activity of these endocannabinoids along with their attachment to cannabinoid receptors is known as the Endocannabinoid system (ECS). This system is known to regulate many physiological processes in humans, such as sleep, pain perception, mood, and the immune response towards various infections. 

CB1 receptors are found mainly in the central nervous system (brain and spinal cord), while CB2 receptors are found mainly in the peripheral tissues as well as the immune system. Unfortunately, there is no solid evidence to suggest that cannabinoid receptors are found in the airways of humans. However, these receptors are well expressed in the immune cells that line the airways of the lungs. For example, CB2 receptors are predominantly expressed on eosinophils and monocytes (immune cells), both of which also express CB1 receptors but to a lesser extent. Eosinophils are well known for their role in promoting chronic inflammation, particularly in patients with allergic asthma. This highlights the potential role of CBD in treating chronic cough.

Cough is known as a symptom of many inflammatory conditions of the airways. Opioids are known as the only prescription-based drugs for the treatment of cough in the United Kingdom. Unfortunately, their efficacy is limited, and they are often associated with many undesired side effects, such as dependence, sedation, and respiratory depression (limited breathing). Based on that, other drugs were studied for their efficacy in treating chronic cough in patients with respiratory illnesses, such as cannabidiol (CBD).

Can Cannabinoids Suppress Cough?

With the lack of effective and safe drugs for the treatment of chronic cough, many novel therapeutic options have been investigated. Recent research indicates that various cannabinoids inhibit the sensory nerve-mediated responses that lead to the activation of the cough reflex. A group of researchers studied the effects of some non-selective cannabinoid receptor agonists (CP 55940 and JWH) on the cough reflex. Both drugs were used for the activation of CB1 and CB2 receptors. It was noted that the CB2 receptor agonist was able to inhibit the transmission of nerve impulses that normally initiate the cough reflex. However, the other CB1 receptor agonist resulted in an opposite effect. These data highlight the promising effects of CB2 receptor agonists in treating chronic cough by suppressing the nerve impulses that normally initiate the cough reflex. So, it was suggested that drugs that lead to the activation of CB2 receptors while inhibiting CB1 receptors would be beneficial in this matter. 

That being said, it should be noted that these findings are based on studies conducted on guinea pigs with chronic cough and not on humans. Therefore, clinical trials on humans are still needed to confirm these actions.

What Are the Effects of Various Cannabinoids (THC, CBD, and others) on Airway Hyperresponsiveness, Inflammation, and Cough?

Cannabis, which constitutes various cannabinoids (THC, CBD, and many others), has been shown to cause bronchodilation (widening of the airways), anti-inflammation, and cough suppression. However, data on the effects of certain cannabinoids (THC or CBD), the interaction between these cannabinoids and cannabinoid receptors, and the underlying mechanism of their actions are still lacking. 

In a recent animal study, a group of researchers compared the effects of a wide variety of cannabinoids (THC, CBD, cannabigerol, cannabichromene, and tetrahydrocannabivarin) on airway inflammation, hyperresponsiveness, and cough. Unfortunately, CBD did not result in a significant effect on the inflammatory cell-mediated immune response. Despite the fact that the frequency of cough was lower in pigs treated with CBD, THC was demonstrated to be the only drug that is effective in preventing airway hyperresponsiveness, alleviating inflammation, and reducing cough frequency. 

To date, there are no data to support the use of CBD in treating both chronic and acute cough in patients with respiratory diseases, particularly chronic obstructive pulmonary disease. Therefore, it is suggested not to use CBD for cough without consulting a physician first.

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