High-throughput screening is an important research tool in drug discovery, which allows rapid testing of a large number of compounds to identify target compounds, where the potent compounds can act precisely at specific protein binding sites to inhibit or activate protein function. However, some compounds were found in high-throughput screening experiments that were not based on the specific interaction between the compound and the protein and showed false positive results for "activity" in different types of target screenings. These compounds are called PAINS, the abbreviation for “Pan-assay interference compounds”. Common PAINS compounds include toxoflavin, isothiazolones, rhodanines, enones etc. Since first publication in 2010 by John Bell, PAINS filters have become widely recognized by the drug discovery industry.

For scientists who needed the PAINS filter, TargetMol created the L4020 NO-PAINS Compound Library that applied the PAINS filter, remaining 9384 small molecules that are suitable for new drug development, signaling pathway research, drug repurposing and other research.