Medicinal Applications of Capsaicin

Substance P is a neurotransmitter which is secreted by neurons in response to noxicous stimuli or capsaicin (Sicuteri et al, 1990). It binds to the NK receptors of primary sensory neurons which then sends pain signals to the brain (Sicuteri et al, 1990). Repeated application of capsaicin leads to substance P over-secretion and depletion (Sicuteri et al, 1990). NK receptors are left unbound and so the pain is no longer felt (Sicuteri et al, 1990).

With this in mind, the following studies investigated capsaicin’s efficacy to treat soft tissue and chronic back pain and rhinitis.

Study 1:

 

Chrubasik et al (2010) found that Finalgon® which contained capsaicin was effective at improving pain symptoms for chronic soft tissue pain and chronic back pain as seen in the figures. Application of the cream was 3/ day for 3 weeks. 

The only issue with the protocol designed by Chrubasik et al (2010) is that the study was conducted in Germany which may or may not affect the efficacy of the treatment if used for people of different backgrounds. Otherwise, the protocol was sound. The subjects were randomized, the study was double-blind and placebo-controlled. Several outpatient clinics (i.e. 23) were contacted ensuring that results are representative of the actual population in Germany. Strict exclusion criteria were applied to remove patients with psychiatric disorders as well as anything that was expected to reduce compliance (such as drug use). Patients were assured patients that itchiness symptoms were not indicative of efficacy thus maintaining the double-blind nature of the study. Lastly, patients were made to discontinue analgesic medications prior to the study so that the effects of the capsaicin were not confounded with that of the patients’ medications.

Study 2:

Ciabatti & D’Ascanio (2009) have shown capsaicin to be an effective treatment for rhinitis that is of unknown cause (IR). This condition can be induced by substance P secretion by nasal mucosal sensory neurons. Since capsaicin is known to deplete substance P stores, the efficacy of a capsaicin containing nasal spray on IR symptoms was investigated. 

This study showed that a minimum capsaicin dose of 4 micrograms/puff/nostril 3 times each day for three days in a row was required to have a statistically significant improvement in symptoms when compared to placebo.

The study had many strengths which includes but is not limited to strict patient inclusion and exclusion criteria, use of 4 week pre and post treatment observations, and the decision to use different nasal spray doses to see which one would be most effective, if effective at all. The biggest drawback in this experiment was that it was not explicitly described as double blind. Also, results were in the form of pain scores by the patients which are highly subjective. A physiological measurement in addition to the patient scores would have been a more objective means of measuring the efficacy of the treatment.

Conclusion:

Both studies were executed fairly well and so there is provide fairly good evidence that both treatments are efficacious.