Enemas containing the anti-inflammatory drug mesalamine are an effective treatment for a distal form of inflammatory bowel disease (IBD). An IBD patient discovered that a generic mesalamine enema was more difficult and painful to use than the proprietary version. A study was initiated to determine whether these differences were measurable in the laboratory using conventional mechanical test equipment. Differences among three bottle types (the proprietary brand and two generic versions) were quantified by mechanical testing. The compressive force required to squeeze the drug from each bottle was measured, tensile testing was performed on the bottle wall, and stiffness of the nozzle tips was studied via bend testing. The thickness of the bottle walls and the inner diameter (ID) of the nozzles were also recorded. The work required to expel the drug from the generic versions during bottle compression was significantly greater than for the proprietary . This was likely due to the wall thickness being greater in the generics; the elastic moduli of the three bottles were similar. The ID of the nozzles was smaller for the generic bottles, suggesting additional resistance to flow. Increased flow resistance was also observed for bottles in which lubricant obstructed the nozzle opening. The work required to bend the nozzle was greater in the generics than in the proprietary . These differences between the generic and proprietary bottles are consistent with the patient’s subjective experience. Poor bottle performance may adversely affect patient compliance with this treatment. Improved bottle design (such as tighter tolerances for wall thickness, nozzle ID, and nozzle stiffness) and manufacturing controls (e.g., preventing the nozzle lubricant from impeding delivery of the drug) could be achieved through the development of a standard specification for enema bottles. An optimal bottle design is suggested.