Temperature influence (20-40 ºC) on the acetaminophen adsorption onto activated carbons with different textures was studied. Different temperature dependences, not explained by kinetic effects, were observed for carbons with different micropore size distributions patterns: adsorption capacity increases for samples Pi-fa/800 and Pi-fa/900, and decreases for carbon S/700. No significant variation was seen for carbon CP. The 1H NMR spectroscopic analysis of the adsorbed phase proved that during the adsorption process exist the conditions required to promote the formation of acetaminophen oligomers which have constrained access to the narrow microporosity. The rotation energy of the dihedral angle between monomers (estimated by electronic DFT methods) showed that conformations in the planar form are less stable than the non-planar conformation (energy barrier of 70 and 23 kJ mol-1), but have critical dimensions similar to the monomer and can access most of the micropore volume. The enthalpy change of the overall process showed that the energy gain of the system (endothermic) for Pi-fa samples ( 40 kJ mol-1) was enough to allow a change in the dimer, or even larger oligomers, conformation to the planar form. This will permit adsorption in the narrow micropores, thus explaining the uptake increase with temperature. Non-continuous micropore size distributions centered at pore widths close to the critical dimensions of planar form seem to be crucial to a positive evolution of the adsorption capacity with temperature.