This disclosure relates to amides, aryl sulphonamides, aryl ureas, and α,β-diketones derivatives useful as carboxylesterase esterase inhibitors. The disclosure is also directed to the use of these compounds as selective human intestinal carboxylesterase inhibitors and insect carboxylesterase inhibitors. The disclosure is also directed to pharmaceutical compositions and pesticide formulations containing these compounds, and to methods for treating or ameliorating the toxic effects following administration of drugs such as cancer therapy drugs, treating or ameliorating the effects of a drug overdose, and to the use of the compounds for increasing the effectiveness of insecticides and pesticides.