The overall objective of this study was to develop an analytical method to contribute to the assessment of the exposure of humans to plastic additives based on the use of a new polydimethylsiloxane-based stir bar extraction method. The method focuses on a list of 21 contaminants, including 18 plastic additives and 3 degradation products. They are analysed by ultra-high performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) after a stir bar sorptive extraction from urine using a home-made stir bar. Thus, the paper focuses on the optimisation of the extraction method. The limits of quantification are variable from one substance to another, but they fall between 0.1 and 305 ng mL−1. The sample preparations lead to recoveries of up to 90% in water and 80% in urine. The method was successfully applied to 15 human urine samples. Among the targeted plastic additives and their degradation products, 7 compounds were quantified in samples at concentrations ranging from 0.3 ng mL−1 to 42.7 ng mL−1.