expression, godan verb (-ru)
go to extremes; go too far; go overboard
Used when someone takes an action or opinion to an unreasonable extreme, often with a negative connotation.
彼は節約に極端に走って、必要なものまで買わなくなった。
He went to extremes with saving money and stopped buying even necessities.
ダイエットで極端に走ると、健康を害するよ。
If you go overboard with dieting, you'll harm your health.