Someone who's intoxicated has had too much to drink. Visit an Irish pub on St. Patrick's Day and you're sure to see at least one intoxicated person.
When you describe someone as intoxicated, you usually mean that he's been drinking alcoholic beverages until he feels dizzy and sick. You can also use the word to talk about someone who's really excited or happy about something: "She was intoxicated by Paris the minute she stepped off the airplane." Before intoxicated was first used to mean "drunk" in the 1570's, it meant "poisoned," which especially makes sense when you know the Latin root word, intoxicare, "to poison."