Density, ultrasonic velocity and viscosity of four pharmaceutically significant drugs were measured in methanol at 25°C. The apparent molar volume (φ v ), apparent molar compressibility (φ K ) and the viscosity B-coefficient were calculated from the experimental data. The variation of φ v and φ K with a drug concentration is linear. Values of φ v o and φ K o are used to understand solute-solvent interactions. φ v o and B-coefficient show wide divergence depending on the size, shape and structure of a drug, while φ K o are close to each other for all the four molecules. The first two parameters show differential solute-solvent interactions, while φ K o show that the drugs compress the solvent to the same extent. This observation is supported by B/φ v o and solvation numbers (S n ) of the drugs.