The drug will have pernicious effect on your health.

Solution (By Examveda Team)

Pernicious : having a harmful effect, especially in a gradual or subtle way.
Beneficial : resulting in good; favourable or advantageous.
Prolonged : continuing for a long time or longer than usual; lengthy.
Ruinous : disastrous or destructive.
Pornographic : constituting or resembling pornography; obscene.

Antonym of Pernicious is Beneficial