User blog comment:Omega natsu2/Chapter 365: Fairy in the Jail!, Predictions./@comment-112.203.211.177-20131219235849/@comment-7418318-20131220200053

We never actually saw any of them take a sip.

In all the pictures Erza only sniffed it and while Mira had the cup at her lips, the angle of the cup wouldn't even allow the liquid to touch her lips. So maybe they really didn't drink any.

But maybe the steam alone was enough to induce sleep, who knows...