Their persistence and wide consumption identify pharmaceuticals as "emerging pollutants". The complexation of pharmaceuticals containing adamantine ring structures and their model substances with humic acids (HA) of different origins was compared using fluorescence spectroscopy as a function of pH, humic acid concentration, ionic strength, and molecular mass of HA. Binding constants between the studied pharmaceuticals and humic acids were calculated. A combination of dynamic and static quenching processes as indicated by nonlinear Stern-Volmer plots and high K(d) values were positively correlated with the concentration of carboxyl groups in the studied humic acids. For basic functional group-containing pharmaceuticals, the complexation was driven by cation exchange and hydrophobic interactions depending on the properties of the interacting compounds.