High Quality Content by WIKIPEDIA articles! An enzyme inhibitor is a molecule that binds to enzymes and decreases their activity. Since blocking an enzyme`s activity can kill a pathogen or correct a metabolic imbalance, many drugs are enzyme inhibitors. They are also used as herbicides and pesticides. Not all molecules that bind to enzymes are inhibitors; enzyme activators bind to enzymes and increase their enzymatic activity, while enzyme substrates bind and are converted to products in the normal catalytic cycle of the enzyme.