IntroductionCancer is a disease caused by genetic changes and disordered cell growth with high incidences over the years. Conventional treatments such as chemotherapy act on cells that are in constant cell division, however, frequently they are not selective to cancer cells and can damage healthy cells. For this reason, side effects such as nausea, dizziness, hair loss, weight loss, and fatigue are reported by patients. Moreover, some cancers present resistance to chemotherapy treatment. Therefore, studies focus on functional and natural products, especially those rich in bioactive compounds, such as capsaicin, could be used as chemotherapy adjuvant to improve treatment response and decrease side effects. MethodsIn this scenario, we conducted a review with 75 articles regarding the anticancer activity and chemotherapy response improvement of capsaicin via cancer hallmark modulation. Results/DiscussionIn this scenario, we reviewed the anticancer activity and chemotherapy response improvement of capsaicin via cancer hallmark modulation. This natural bioactive molecule ameliorates chemotherapy response by several cancer pathway regulations. ConclusionsThis review was able to show that capsaicin has a remarkable effect as an adjuvant to improve chemotherapy and reduce side effects.