Depression is a mental illness that affects nearly 320 million people around the world. It is the second-highest cause of work disability, and some projection analyses predict it could become the first by 2020. Depression is a devastating condition for the person who suffers from it and also for the people around them.
Although there are several medications for depression, ~30% of patients have little response to these treatments. Moreover, all the medications for depression have undesirable side effects to some degree. Thus, the search for new and more efficient treatments for this disease is highly desirable.
In this respect, researchers from Mexico’s universities have recently found that capsaicin, the pungent ingredient of chili peppers, exhibits antidepressant-like properties. As is commonly known, chili is a fruit widely used in the gastronomy of many countries in the world, among which Mexico is one of the main consumers.
Using an animal model broadly employed for the screening of potential antidepressant drugs, a forced swimming test in rats, the researchers discovered that low doses (50 to 250 µg/kg) of capsaicin reduced the immobility time (the index of antidepressant-like behavior) of the rats subjected to this test. These low doses of capsaicin were as effective as a saturating dose of amitriptyline, which is a tricyclic antidepressant drug used for the treatment of depression. Moreover, ineffective low doses of capsaicin (1 pg/kg, and 1 ng/kg) were indeed effective when they were combined with a small dose of amitriptyline.
Capsaicin is a physiological agonist of the transient receptor potential cation channel subfamily V member 1 (TRPV1). This type of cell membrane receptors was discovered not long ago, and they were almost exclusively attributable to the transmission of noxious information. However, TRPV1 channels were found to be extensively expressed in many areas of the brain, especially in those structures involved in the control of emotions (limbic system).
In the study performed by the Mexican researchers, a non-pungent agonist for the TRPV1 channels, named palvanil, showed similar antidepressant-like properties as the pungent compound, capsaicin. This result could be potentially relevant for people who not tolerate the pungent flavor of capsaicin. Likewise, the researchers found that capsaicin did not have stimulating effects on the muscle, and the general locomotor activity, suggesting that its antidepressant-like effects were exclusively on the nervous system, where antidepressant drugs act.
Finally, unlike many antidepressant drugs used nowadays, capsaicin did not induce anxiogenic-like behaviors. It is certainly premature to consider capsaicin as an antidepressant treatment; however, this investigation offers promising results. More investigation is needed to determine if capsaicin is as effective in humans as it was in rodents. Assuming that capsaicin has antidepressant properties in humans, it would be a favorable improvement in the treatment of depression because the low doses employed in this compound envision much lesser collateral side effects than those provoked by antidepressant drugs currently used. Perhaps the good mood of Mexican people is in part a result of the ingestion of chili.
The results of this investigation were published in the article entitled Capsaicin produces antidepressant-like effects in the forced swimming test and enhances the response of a sub-effective dose of amitriptyline in rats, published in the journal Physiology & Behavior. The research was conducted by Miriam E. Reyes-Mendez, Luis A. Castro-Sánchez, Adán Dagnino-Acosta, Irving Aguilar-Martínez, Azucena Pérez-Burgos, Clemente Vázquez-Jiménez, Eloy G. Moreno-Galindo, from the University of Colima, Fernando J. Álvarez-Cervera, José L. Góngora-Alfaro, from University of Yucatan; Ricardo A. Navarro-Polanco, and the leading author Javier Alamilla, from CONACYT–University of Colima.