Melatonin is an established hormone supplement and has been well recognized for its effect on the circadian cycle to improve sleep, REM (rapid eye movement), and aiding in jetlag recovery. The utility of melatonin extends beyond sleep aid, however. This hormone also possesses less well-known antioxidant action and even robust anticancer activity. Melatonin may be a key supplement for addressing age-related neurologic decline while serving as a valuable adjunctive cancer treatment that reduces drug resistance in tumors and downregulates angiogenesis. In immunotherapy, melatonin activates Natural Killer (NK) cells nested within tumoral tissue and does not have the side effect profile of other immunoreactive agents used for chemotherapy. Since melatonin is found in high concentrations in the brain and other hormone-linked tissues, the relevance of melatonin is increased for the treatment of estrogen-linked cancers. The immunomodulatory effect of melatonin may also help with chronic inflammation seen in patients with autoimmune disorders. All of these effects together represent a unique and versatile therapeutic agent for integrative medicine. No other commercially available drug possesses all of these therapeutic mechanisms while having a very minimal side effect profile and being considered overall to be safe to use. Currently, melatonin is underutilized in medicine, especially in the field of integrative oncology and represents a crucial supportive adjuvant to improve the lives of patients.