Medical Asthma is a chronic respiratory disease that currently affects up to 300 million people worldwide, and was responsible for approximately 250,000 deaths in 2011. Cannabis has been used as a means of treating the symptoms of asthma for millennia, in various medicinal traditions including those of ancient India and China.
Although pain is not necessarily considered to be a primary symptom of an acute episode of asthma, studies have shown that up to 76% of patients experience chest pain during an attack. Generally, asthma-related pain is characterized by a deep ache or sharp stabbing sensation that develops gradually over the first few hours of the attack, and slowly dissipates as the attack recedes.
While there are no studies that specifically investigate the ability of cannabis to treat asthma-related pain, several studies into the general effect of cannabis on asthma have noted subjective improvements in pain. The known bronchodilatory and analgesic effects of certain cannabinoids suggest that they could be useful in managing asthma-related pain both by reducing pressure and constriction in the lungs, and by acting directly at the nociceptors (pain-sensing nerve cells) themselves.
Although asthma is generally thought to have some genetic basis, there is increasing evidence for the fact that the disease may be triggered or caused by bacterial or viral infections in early childhood, which due to their effect on the immune system, leave sufferers susceptible to various allergens and irritants.
An emerging body of research is currently looking into the potential for antibiotics to treat both the short- and long-term symptoms of asthma, and thus far, several studies have pointed to the potential for common antibiotics such as erythromycin and azithromycin to ease the acute symptoms of asthma.
Cannabinoids including THC, CBD, and CBG have been shown to have a broad-spectrum bactericidal effect against many common and infectious pathogens. One group of bacterial agents suspected of being a potential underlying cause of asthma is the Streptococcus genus, which includes S. pneumoniae and S. aureae, has been shown in several studies to succumb to the bactericidal effect of cannabinoids.
Asthma is considered to be a chronic inflammatory condition, as persistent, low-level inflammation has been found to occur in the bronchi and bronchioles even during non-attack circumstances. During an attack, levels of inflammation increase, exacerbating the levels of constriction caused by muscular contractions of the bronchial tissue. Asthma-related inflammation is generally thought to be an immune response to the presence of allergens, although the immune response has not been definitively ascertained and may differ greatly between individuals.
Generally, acute episodes of asthma are treated using bronchodilators as a first line of defence, but in severe cases it is also likely that some form of anti-inflammatory drugs such as steroids or NSAIDs (non-steroidal anti-inflammatory drugs) will be administered.
Cannabinoids are well-known for their anti-inflammatory effects, and while most studies thus far into cannabis and asthma have focused primarily on the bronchodilatory effect, some have also observed a reduction in bronchial inflammation. Furthermore, cannabis is currently being investigated for its ability to produce targeted therapies for immune-modulated inflammatory diseases.
Cannabinoid receptors have been found in human lung tissue, although in relatively low concentrations, and are thought to play a vital role in the regulation of inflammation, muscular contractions and dilations, and various metabolic processes. However, research into the immune-modulated inflammatory response (and how cannabis may assist it) is in its infancy.
The ability of cannabis to act as a bronchodilator is perhaps its most significant property in terms of the treatment of asthma. During an asthma attack, the bronchioles (the branching network of tubes that carry oxygen to the alveoli) become constricted, causing the rate of oxygen flow to drastically reduce.
Generally, the extent of bronchoconstriction during an attack is determined by peak expiratory flow measurements, which are taken from patients and compared to readings taken in normal circumstances. The difference between the normal rate of airflow and the limited airflow during an attack can thus be determined.
Several studies have shown that administration of cannabis in various forms can significantly improve bronchoconstriction both during an asthma attack and in normal circumstances (sufferers of severe asthma often have lower-than-average airflow compared to non-asthmatics even when an attack is not occurring).
In the early 1970s, a spate of studies were published investigating the bronchodilatory effects of cannabis for asthmatics. A study in 1973 observed that cannabis smoke—unlike that of tobacco—caused a bronchodilatory effect; a 1974 study found that while the bronchodilatory effect of cannabis was weaker than that of isoproterenol, its effects lasted longer, and a 1976 study found that cannabis was as equally effective as salbutamol, although the latter achieved maximal bronchodilation somewhat more rapidly.
As with much of cannabinoid science, there are complicating factors. For example, a recent study found that the endogenous cannabinoid anandamide could actually exert a biphasic (two-stage) effect on lung tissue: it strongly inhibits bronchial constriction in the presence of an allergen or irritant (in this case capsaicin) but causes bronchial constriction in normal circumstances, i.e. when no irritant is present. Indeed, some patients administered with THC have reported experiencing bronchial constriction. Thus, further research is needed to determine exactly how cannabinoid treatments should be used across the board.
It is thought that cannabis can exert a bronchodilatory effect mostly through its ability to reduce inflammation. However, it is also thought that cannabis’ ability to reduce muscular spasms (involuntary contractions) plays a significant role in the management of bronchoconstriction during an asthma attack. The bronchi and bronchioles are composed of smooth muscle, and during an attack, they contract and narrow as well as becoming inflamed.
In a study published in 2014, researchers took bronchial lung tissue from 88 human patients and subjected it to electrical field stimulation to cause the muscle tissue to contract. They then administered THC, the endogenous cannabinoid 2-AG, and various synthetic agonists of CB-receptors type I & II. They found that certain agonists of the CB1-receptor, including THC, reduced muscle contractions in a dose-dependent manner. Furthermore, it was observed that the endogenous cannabinoid 2-AG had no effect.
The ability of cannabis to act as an expectorant is somewhat controversial. It has been used as such for thousands of years, and appears in the ancient pharmacopoeiae of China and India, but modern research has been sparse and has thus far yielded only ambiguous results.
Countless people throughout the world report an expectorant effect after smoking or vaporizing cannabis. If it were noted only in smokers of cannabis, it could easily be dismissed as a result of the irritation caused by smoke particles ; the fact that an effect is experienced even when inhaling vapour suggests that an active substance in cannabis is causing it.
However, most existing research actually points to the propensity of cannabis to cause production of mucus. For example, a study published in 2014 observed increased mucus secretions in habitual cannabis smokers, along with damage to the tissues of the airways. Thus, further research into the expectorant and decongestant effects of cannabis could be advantageous.