All virtual screenings were performed by docking program PLANTS (version 1.1)27 . PLANTS combines an ant colony optimization algorithm with an empirical scoring function30 (link) for the prediction and scoring of binding poses in a protein structure. For each compound, 25 poses were calculated and scored by the chemplp scoring function at speed setting 2. The binding pocket of H1R was defined by the coordinates of the center of co-crystallized doxepin in the 3RZE structure and a radius of 10.8 Å (which is the maximum distance from the center defined by a 5 Å radius around doxepin). All other options of PLANTS were left at their default setting.