Question

A drug used to counteract the effect of an excessive drug toxicity level is called a/an

Answer 1

The term drug overdose (or simply overdose or OD) describes the ingestion or application of a drug or other substance in quantities greater than are recommended or generally practiced.[2] An overdose may result in a toxic state or death. The word "overdose" implies that there is a common safe dosage and usage for the drug; therefore, the term is commonly only applied to drugs, not poisons, though even poisons are harmless at a low enough dosage.

Answer 2

the answer would be antidote