Studies of the interactions between paracetamol, chosen as model active ingredient, and PEG 1500, a pharmaceutical carrier, are conducted in the solid state. Solid dispersions of PEG 1500 and paracetamol were prepared in different mass ratios. Two temperature cycles are then applied and the characterization is carried out by DSC and X-ray powder diffraction. Following this, a phase diagram is established for each cycle. On second heating, the metastable Form II of paracetamol is obtained within the PEG-based matrix. However, on the second heating, for paracetamol contents higher than 65%, Form I or form II is obtained randomly.