Are people more honest when they're drunk?

The old Latin adage "In vino veritas" — meaning "In wine, there is truth" — is just one of a litany of sayings perpetuating the idea that alcohol is a sort of truth serum. The phrase is attributed to Pliny the Elder, a Roman scientist, historian and soldier, though similar aphorisms can be traced back even further, to ancient Greece.

But does alcohol really make people more honest? The answer is both yes and no, experts told Live Science.

Alcohol "makes us more likely to say whatever's on our minds," said Aaron White, leader of the National Institute on Alcohol Abuse and Alcoholism's Epidemiology and Biometry Branch. "In some cases, that could be the truth. In some cases, it could be what you think is the truth in your intoxicated state."

So there's definitely a higher likelihood that someone will speak their mind after a few drinks. But there's also a chance that they will say something that feels real while drunk but that they wouldn't take seriously while sober. For example, a drunk friend might make bold promises they're going to move cities or quit their job only to take them back the next morning.

While an extensive online search didn't turn up any direct results for research on how alcohol influences honesty, studies about alcohol's impact on personality, emotion and cognition help support this idea.

For example, a 2017 study in the journal Clinical Psychological Science explored how participants' personalities changed after they'd consumed enough vodka lemonades to bring them to 0.09% blood alcohol concentration — just over the federal legal driving limit in the U.S. and England. Outside observers remarked that the biggest change in participants' personalities after drinking was that they became much more extroverted. Though the study didn't investigate whether alcohol was a truth serum, it makes sense that someone who feels more at ease in a social setting is also more likely to be candid.

Alcohol's ability to help people come out of their shell may help them say what's on their minds, but White says its effects on emotions can make those thoughts more mercurial.

Related: How a hangover affects your brain the next day

"We generally find that drinking alcohol tends to intensify our emotions," Michael Sayette, a professor of psychology at the University of Pittsburgh, told Live Science in an email. "We may find ourselves smiling more and speaking more loudly in pleasant interactions, but perhaps, as the researcher [professor emeritus at Stanford University] Claude Steele put it, we might also be more likely to cry in our beer in less-pleasant situations."

Those heightened emotions might lead people to say what's on their sober mind, but they can also put someone in a volatile state where they say something they don't really mean or deeply regret later. It's similar to how drinking makes some people more likely to become violent or to gamble — actions that may cross their sober minds, but they would have the wherewithal to avoid.

"Because alcohol can change our thoughts and feelings, it's unsurprising that behaviors can also change," Sayette said. "Alcohol can lead our behaviors to become more extreme."

These effects stem from alcohol's ability to cause disinhibition, which means a person is more likely to act on their impulses. This happens because alcohol dampens signals in the prefrontal cortex, a region of the brain that regulates behavior and controls impulses, White explained.

What's more, alcohol also suppresses the amygdala, a structure deep in the brain known for sparking feelings of fear and anxiety. While a person is sober, the amygdala generally sends out warning signals that can stop a person from saying or doing things that could lead to a social faux paus, but those signals quiet down after a few drinks.

So is there really "veritas in vino"?

Sure, people might be more likely to divulge secrets after a few glasses of wine — but they're also likely to blurt out something they don't really mean and will regret the next morning. The effects of alcohol on the mind are simply too complex to have a black-and-white effect on honesty.

"Alcohol is not a truth serum," White said. "That's for certain."