stone sober
Completely sober; not intoxicated to any degree by drugs or alcohol. I'm stone sober, so I'll drive us home. No, I'm not high—I've been stone sober from the day I started working here!
stone(–cold) sober
and cold soberabsolutely sober. I am stone-cold sober, or I will be by morning anyway. I found the secret to waking up cold sober. Don't drink.