SLC18A1 encodes the vesicular monoamine transporter 1 (VMAT1), a presynaptic transporter that packages monoamine neurotransmitters including dopamine, noradrenaline, serotonin, and histamine into synaptic vesicles for controlled release 1. The protein functions through proton antiport mechanism, enriching monoamines approximately 10,000-fold within vesicles 1. Structural studies reveal VMAT1 adopts different conformational states during transport, with a lumenal-open conformation facilitating monoamine accumulation and a cytoplasmic-open state triggered by protonation 1. A functionally significant polymorphism (Thr136Ile, rs1390938) affects transport activity, with the 136-Thr variant showing 20-50% lower transport activity compared to 136-Ile 2. This polymorphism has been associated with various psychiatric conditions including bipolar disorder, schizophrenia, and methamphetamine use disorder 345. The variant also correlates with alcohol withdrawal severity, suggesting a role in addiction pathways 6. Additionally, germline deletions in SLC18A1 increase colorectal cancer risk, with reduced expression observed in tumor tissues 7. These findings establish SLC18A1 as a critical component of monoaminergic neurotransmission with implications for neuropsychiatric disorders and potentially cancer.