6484. The newly found drug on the epidemic was not at all deleterious.

✅ The correct answer is option C.
Effective : successful in producing a desired or intended result.

Intoxicating : (of alcoholic drink or a drug) liable to cause someone to lose control of their faculties or behaviour.

Noxious : harmful, poisonous, or very unpleasant.

Successful : accomplishing a desired aim or result.

Deleterious : causing harm or damage.

Synonym of Deleterious is Noxious