In our paper ‘Do initial concentration and activated sludge seasonality affect pharmaceutical biodegradation rate constants?’ we evaluated potential relationships between first-order biodegradation rate constants (kb) of nine pharmaceuticals and initial concentration of the selected compounds, and sampling season of the used activated sludge inocula. Four-day bottle experiments were performed with activated sludge from wastewater treatment plant (WWTP) Groesbeek, the Netherlands, of two different seasons, summer and winter, spiked with two environmentally relevant concentrations (3 and 30 nM) of pharmaceuticals. Concentrations of the compounds were measured by LC-MS/MS, microbial community composition was assessed by 16S rRNA gene amplicon sequencing and kb values were calculated. Wastewater measurements during the experiment included: dissolved inorganic matter, total suspended solids, pH, ammonium, nitrate and nitrite concentrations. At the start of the experiment, WWTP conditions were collected on: ammonium and nitrate concentrations, total suspended solids, oxygen and temperature. The biodegradable pharmaceuticals, ranked from high to low biodegradation rates, were acetaminophen, metformin, metoprolol, terbutaline, and phenazone. Carbamazepine, diatrizoic acid, diclofenac and fluoxetine were not converted. Summer and winter inocula did not show significant differences in microbial community composition, but resulted in a slightly different kb for some pharmaceuticals. Likely microbial activity was responsible instead of community composition. In the same inoculum different kb values were measured, depending on initial concentration. In general, biodegradable compounds had a higher kb when the initial concentration was higher. This demonstrates that Michealis-Menten kinetics theory has shortcomings for some pharmaceuticals at low, environmentally relevant concentrations and that the pharmaceutical concentration should be taken into account when measuring the kb in order to reliably predict the fate of pharmaceuticals in the WWTP.The data can be found in the following files, containing primary data:i) Van_Bergen_etal_experimental_wastewater_conditions (.xlsx, .csv or .ods), with data of dissolved inorganic matter, total suspended solids, pH, ammonium, nitrate and nitrite concentrations during the experiment.ii) Van_Bergen_etal_WWTP_conditions (.xlsx, .csv or .ods), with data of ammonium and nitrate concentrations, total suspended solids, oxygen and temperature at the time of sampling at WWTP Groesbeek.iii) Van_Bergen_etal_pharmaceutical_concentration (.xlsx, .csv or .ods), with data of the concentrations over time of the following pharmaceuticals: acetaminophen, carbamazepine, diatrizoic acid, diclofenac, fluoxetine, metformin, metoprolol, phenazone and terbutaline.