Thapsigargin is non-competitive inhibitor of the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA). Structurally, thapsigargin is classified as a sesquiterpene lactone, and is extracted from a plant, Thapsia garganica. It is a tumor promoter in mammalian cells. Thapsigargin treatment and the resulting ER calcium depletion inhibits autophagy independent of the UPR response. Thapsigargin is useful in experimentation examining the impacts of increasing cytosolic calcium concentrations and ER calcium depletion.