5-Amino-1-methylquinolinium (5-Amino-1MQ), with the molecular formula C10H11N2+, is a small molecule and selective inhibitor of nicotinamide N-methyltransferase (NNMT), an enzyme involved in the methylation of nicotinamide and other pyridines, which plays a critical role in cellular metabolism and epigenetic regulation. By inhibiting NNMT, 5-Amino-1MQ increases intracellular levels of nicotinamide adenine dinucleotide (NAD+), a vital coenzyme in metabolic processes, thereby enhancing energy expenditure, fat oxidation, and mitochondrial function. This mechanism has been studied for its potential therapeutic applications, including the reduction of fat cell size and body weight, improvement of insulin sensitivity in metabolic disorders such as type 2 diabetes, and promotion of muscle regeneration by supporting stem cell activity. Additionally, 5-Amino-1MQ has shown promise in preclinical studies for its anti-aging effects, as elevated NAD+ levels are associated with improved cellular repair and longevity, and for its selective inhibition of cancer cell proliferation by disrupting tumor metabolic pathways. Research continues to explore its pharmacokinetic profile, safety, and efficacy in clinical settings for these diverse applications.