The path of the contaminant from its discharge in the environment to the complete degradation to inorganic salts, water and carbon dioxide is rather long and complex. Although the state of knowledge on this subject is still insufficient, it has been demonstrated that some transformation products (TPs) may be as harmful as their parent compounds, in addition, they may be much more harmful in an environmental situation, where they occur in mixtures. In this study, two sampling techniques, passive and grab sampling, were compared for qualitative analysis of pharmaceutical TPs in urban WW effluents. Results demonstrated better suitability of passive sampling mainly due to the better quality of MS2 spectrum. The non-target screening revealed the occurrence of 13 TPs in secondary treated effluents (i.e., tramadol N-oxide, N,O-didesmethyltramadol, amisulpride N-oxide, O-desmethylvenlafaxine N-oxide, O-desmethylvenlafaxine, N-desmethylvenlafaxine, venlafaxine N-oxide, gabapentin lactam, O-desmetyltramadol, clarithromycin N-oxide, hydroxyclarithromycin, hydroxycarbazepine, and carbamazepine-10,11-epoxide). Retrospective analysis of the previously acquired data by high-resolution mass spectrometry was used to reveal the fate of these compounds during the treatment in constructed wetlands. Among identified compounds, N-oxides and carabamazepine-10,11-epoxide appeared to be the most recalcitrant, alongside amisulpride, gabapentin, and carbamazepine. The results obtained offer insight into the fate of pharmaceutical TPs and may serve as a guideline for the prioritization of contaminants TPs based on their persistence during the treatment and assist in the design of treatment systems.