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

Answer: 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