IPA: /ˈoʊvərˌdoʊsɪdʒ/
KK: /ˈoʊvərˌdoʊsɪdʒ/
Taking more of a medicine than is safe or recommended.
The doctor warned about the dangers of overdosage when using painkillers.
Overdosage → It is formed from "over-" (meaning excessively) and "dosage" (from the French "dosage", meaning the amount of a medicine or drug). The word refers to the excessive amount of a drug or medicine taken.
Think of taking an 'excessive' amount ('over-') of a 'medicine amount' ('dosage') — that's why overdosage means taking too much of a drug.
No commonly confused words.