Mineral scale deposition and pipeline corrosion are two of the most common challenges that require chemical treatment in oil wells. Combination products including scale inhibitor (SI), corrosion inhibitor (CI) packages, surfactants, and other chemical additives are well accepted as an integrated solution to flow assurance and asset integrity problems. In this work, a case study in the Permian Basin field demonstrates a certain type of combination product exhibiting lower performance than expected. The raw material interference on the scale inhibitors was investigated and presented with detailed laboratory data. A series of laboratory tests were conducted to investigate the impacts on performance from the chemicals in the combination product. In the dynamic tube blocking test, the phosphonate-based SI shows much weaker performance in the presence of certain active CI components, while other raw materials (surfactants and quaternary amine) had a minor effect. Further bottle tests revealed a calcite inhibition drop from complete inhibition to 30% and 40% inhibition in the two phosphonate-based SI chemistries in the presence of the active component, respectively. In the additional barite inhibition tests, no significant impact on the SI performance was observed. Contrary to the previous literature reports about common CI chemicals, this active component expressed significantly adverse impacts on the SI performance for calcite prevention. This study demonstrates a root cause analysis for the adverse effect of certain active CI components on the scale prevention and suggests the impact of the CI package on SI should be carefully investigated in the product selection. A thorough evaluation of combination product performance is recommended before the field application.