Abstract: Nicotinamide (NAM) is the amide form of niacin and one of the precursors of nicotinamide adenine dinucleotide (NAD⁺). NAM can be used as a dietary supplement or clinical therapeutic drug to replenish NAD⁺ levels in the human body and participate in key bodily functions such as cellular metabolism and DNA repair. NAM has the advantage of low cost, wide availability, and sound biosafety. It also has multiple biological functions, including antibacterial effect, anti-inflammatory effect, and modulation of cellular immunity, producing significant ameliorative effects on skin and neurodegenerative diseases. However, most studies on NAM are still at the laboratory stage. Herein we reviewed the role and mechanism of NAM in the prevention and treatment of oral and systemic diseases, explored its potential as clinical therapeutic medication, provided some basis and references for the clinical application of nicotinamide in the prevention and treatment of various diseases, and discussed its prospects for future research and application.