This is the consequence of one chemical (or a group of chemicals) interacting: the situation in which the combined effect of two or more chemicals is less than the simple sum of their independent effe [..]

This is the consequence of one chemical (or group of chemicals) counteracting the effects of another chemical, the opposing chemicals cancel out each other's effects. (09 Oct 1997)

  A response to a mixture of chemicals or combination of substances that is less than might be expected if the known effects of individual chemicals, seen at specific doses, were added together.