Electrogenic antiporter that exchanges one cationic monoamine with two intravesicular protons across the membrane of secretory and synaptic vesicles. Uses the electrochemical proton gradient established by the V-type proton-pump ATPase to accumulate high concentrations of monoamines inside the vesicles prior to their release via exocytosis. Transports a variety of catecholamines such as dopamine, adrenaline and noradrenaline, histamine, and indolamines such as serotonin (PubMed:23363473, PubMed:37914936, PubMed:38081299, PubMed:38517752, PubMed:8643547). Regulates the transvesicular monoaminergic gradient that determines the quantal size. Mediates somatodendritic dopamine release in hippocampal neurons, likely as part of a regulated secretory pathway that integrates retrograde synaptic signals (By similarity). Acts as a primary transporter for striatal dopamine loading ensuring impulse-dependent release of dopamine at the synaptic cleft (By similarity). Responsible for histamine and serotonin storage and subsequent corelease from mast cell granules (PubMed:8860238). {ECO:0000250|UniProtKB:Q01827, ECO:0000250|UniProtKB:Q8BRU6, ECO:0000269|PubMed:23363473, ECO:0000269|PubMed:37914936, ECO:0000269|PubMed:38081299, ECO:0000269|PubMed:38517752, ECO:0000269|PubMed:8643547, ECO:0000269|PubMed:8860238}. This is the function of SLC18A2 (solute carrier family 18 member A2, Ensembl gene identifier ENSG00000165646).