in vino veritas
Definition from Wiktionary, the free dictionary
From Latin: in (“in”) + vīnō, the ablative singular of vīnum (“wine”) + vēritās (“truth”). Thus, “in wine there is truth”. First attested, as volgoque veritas iam attributa vino est, in the Naturalis Historia (XIV, 141) of Pliny the Elder.
- drunken folks speak truth, one tells the truth under the influence of alcohol
Usage notes 
- Used to refer to the effect of alcohol on reducing inhibitions, allowing someone to say what they truly think.
- Secondarily, used to suggest that one's perceptions and emotions when drunk are more real than when sober.
one tells the truth under the influence of alcohol