pernicious, baneful, noxious, deleterious, detrimental mean exceedingly harmful. pernicious implies irreparable harm done through evil or insidious corrupting or undermining.
// the claim that pornography has a pernicious effect on society baneful implies injury through poisoning or destroying.
// the baneful notion that discipline destroys creativity noxious applies to what is both offensive and injurious to the health of a body or mind.
//noxious chemical fumes deleterious applies to what has an often unsuspected harmful effect.
// a diet found to have deleterious effects detrimental implies obvious harmfulness to something specified.
// the detrimental effects of excessive drinking