Diflunisal (Apollo Scientific Ltd, 98%), adenine (TCI, 98%), caffeine (TCI, 98%), theobromine (Sigma-Aldrich, 98%), xanthine (Sigma-Aldrich, 99%), rosmarinic acid (Thermo Scientific, >97%), and riboflavin (Sigma-Aldrich, 99%) were used as received. Acetone, ethanol, ethyl acetate and dichloromethane were selected as solvents for the liquidassisted grinding tests. Slurry experiments were conducted using 1 mL of ethanol, hexane or acetonitrile. Diflunisalcaffeine co-crystal in the form of a white microcrystalline powder was obtained by grinding 100 mg (0.4 mmol) of diflunisal and 78 mg (0.4 mmol) of caffeine for 20 minutes, after which drops of ethanol were added, continuing the liquid-assisted grinding for a further 20 minutes and repeating the adding of ethanol every 5 minutes. Diflunisaladenine was obtained by slurry in ethanol: 100 mg of diflunisal (0.4 mmol) and 54 mg (0.4 mmol) of adenine were mixed in a 10 mL beaker, adding 1 mL of ethanol. The suspension was left under stirring for two days at room temperature. After solvent evaporation, the sample was obtained in the form of a microcrystalline white powder. The powder samples were characterized by FT-IR ATR (Supporting Information, Figs. and) and solid-state NMR (Supporting Fig. and).