The dataset extraction can be restricted to only include literature sources. This changes some of the values in the pChEMBL columns and in columns which depend on them, i.e., the ligand efficiency metrics. Values in columns related to the first appearance of the compound or compound-target pairs change as well. Since this restriction changes values in several columns, limiting the dataset to literature sources is not available as a filtering column. Instead, it is a parameter that is set before extracting the dataset. By default, the dataset is limited to include only literature sources to ensure consistency. ChEMBL is based on a variety of different sources, some of which have not been added on a regular basis. One of these sources is BindingDB 10 . BindingDB curated patent data from 2013 onwards and data from BindingDB was included into ChEMBL until 2016. Therefore, there is a large amount of patent data for the years 2013-2016 in ChEMBL in comparison to all other years. The number of compounds from BindingDB compared to the number of compounds from literature sources can be seen in Figure . When including all sources, the percentage of compounds first published in 2015 and 2016 is more than double the percentage of compounds in the years 2012 and before and after 2016 (Figure ). In the years from 2014 to 2016, kinases are overrepresented compared to all other years before and after (Figure (c)). These effects are not seen when the dataset is limited to literature sources (Figure and (e)). To exclude any effects from this skewed distribution, the default option is set to include only literature data. The option can be changed to include data from all sources in ChEMBL, but we advise caution when using the resulting dataset.