Marmin, a natural product isolated and purified from the herbs of Citrus maxima with potent anti-ulcer, antibacterial, fungicidal, and algicidal properties, can inhibit contraction of the guinea-pig tracheal smooth muscle, especially by interfering histamine receptor, inhibiting the histamine release from mast, inhibiting intracellular Ca2+ release from the intracellular store and the Ca2+ influx through voltage-dependent Ca2+ channels, is potential to develop as antihistamine agents, especially as histamine H1 receptor antagonists by interacting with amino acid residues, Asp107, Lys179, Lys191, Asn198, and Trp428 of histamine H1 receptor, shows a cell-growth inhibitory effect against L1210 and K562 in vitro.