Thin polymer films are produced for pharmaceutical purposes from a solution in water and polar solvent. These coatings contain also a heavy solvent with the active substance as solute. A global analysis is presented here of the drying rate in terms of average content for each component, i.e. water, heavy solvent and active substance. The results are used to better the global drying process. The quality of the final product imposes to know the local distribution of the key products. The use of Laser Scanning Confocal Microscopy (LSCM) on two molecules is proposed here; the active substance and the heavy solvent. Combining the two set of results, one is able to determine the cases of maldistribution of the active substance and of eventual crystallisation which in turn will have consequences on storage and successful transdermal delivery of the drug.