Fatally overdosing on opium is more difficult than overdosing on acetaminophen, or many other OTC drugs you can pick up from your local pharmacy.

The alkaloids in opium are STRONG emetics. While it is certainly possible to fatally overdose, it is far more likely one would vomit for a few hours and be fine, assuming they did not consume far above a 'normal' amount for their bodyweight.

Which, by the way, is true of alcohol as well.