Loopy

"The anti nausea medication may cause him to be loopy."

Loopy = Balmy, barmy, bats, batty, bonkers, buggy, cracked, crackers, daft, dotty, fruity, haywire, kooky, kookie, loco, loony, nuts, nutty, round the bend, around the bend, wacky, whacky -- (informal or slang terms for mentally irregular)