Active pharmaceutical ingredient (APIs) are frequently delivered to the patient in the solid-state as part of an approved dosage form (e.g., tablets, capsules, etc.). Drug compounds tend to crystallise into different crystal forms, some of which incorporate solvent (water). We are investigating the factors leading to water incorporation. Cimetidine (CIM) exists in four polymorphs and a monohydrate, and our preliminary data shows interaction between the guanidine NH group and water at high concentrations, which is potentially critical for the formation of the monohydrate. We thus propose to measure neutron total scattering on SANDALS for CIM in neat DMSO solution and in the presence of 5 equivalence of water to elucidate the molecular interaction in solution.