About 20% of Americans in the last 30 days have had an episode of heavy drinking.
Now, a new study is calling into question the term "functional alcoholic" and taking a closer look at alcohol's real physical and emotional impact.
For one young woman, that impact has become all too personal.
Heavy drinking was part of Gillian Ruez' childhood.
"My dad was an alcoholic," Ruez said.
One time as a teenager, Ruez drank two tall cans of beer and didn't think twice before getting behind the wheel.
"Blasted my music, sped off and I hit railroad tracks," she said.
"My car literally did a 360 flip to the point where it landed on a light pole."
Now 22, she says her drinking still continued.
During the pandemic, high school classes went online and she turned to more alcohol. Gillian thought she could carry on without people noticing.
"I was buying about two liters of vodka a day and consuming it, for about a year," she said.
Dr. Timothy Fong with UCLA health, a specialist in addiction psychiatry, says this became more common during the pandemic.
"During the pandemic we saw more people drinking to cope with the stress," Fong said. "We also saw alcohol being delivered to homes."
He says a new study about heavy drinkers reveals what experts have suspected all along.
"You can still get impaired at four or five drinks throughout the day or evening. Just because someone can take in 'a lot of alcohol' in a short period of time and not appear intoxicated or passed out, that doesn't mean alcohol is not harming their body, their brain or their mind," he said.
Fong says binge drinking - consuming five or more drinks for a man or four or more for a woman - and high intensity drinking, which is about double that, is on the rise.
And experts say no matter how tolerant you think you are, it's not sustainable.
Even mild drinking can escalate.
"If you're drinking, and it creates some kind of problem in your life, and it continues to happen over and over, that is a sign of alcohol-use disorder," Fong said.
The National Institutes of Health says only about 10% of people with alcohol use disorder go into treatment.
Gillian sought rehab at Action Family Counseling in Santa Clarita.
She wears an alcohol monitor on her ankle.
"It takes my sweat glands every 30 minutes," she said.
She's still in the tender stages of recovery, but with the support of the program, Gillian finally feels at peace with herself.
"If I can make it through today without drinking, I can do the same thing tomorrow," she said.
"It's just a one-day-at-a-time program."