Almost without exception this statement is true. In this context we can designate a desired effect and one or more toxic effects in relation to a drug.
Toxicity can occur in three different modalities, acute, sub-acute and chronic toxicity.
Acute toxicity is a toxic effect occurring within minutes or hours usually in response to a single dose or exposure to the toxic agent. Identification of this sort of toxicity is often difficult and the unequivocal identification of the cause even more complex. The observer can set quite precise criteria to determine whether the subject is verbose, or in a state of repose. This is a quantal response in that the subject either meets the standard to be included in the state, or they do not. A sort of binary response.