Mariel Hemingway: 'I Want to Break the Stigma of Mental Illness'
08/04/2015 AT 04:35 PM EDT
"It's important to work towards erasing the stigma," she says. "Everybody knows somebody who suffered some mental illness, suicide, addiction or bipolar."
The 53-year-old granddaughter of author Ernest Hemingway has been outspoken about her family's dark past. And in this week's PEOPLE, she talks about her personal connection to the Ryan Licht Sang Bipolar Foundation, which is focused on finding a test for an early diagnosis of bipolar disorder.
Ryan Licht Sang, who was bipolar, was the only son of Joyce and Dusty Sang. One day in 2004, "he stopped taken his medication because he didn't like the side effects, and went into a manic episode," says Hemingway. "After being awake for days, he self-medicated and accidentally overdosed."
"It's tragic when it's misdiagnosed or when it's not diagnosed at all and you just think you have a horribly misbehaved and rebellious child who is actually suffering," Hemingway tells PEOPLE. "That's why this foundation is so important."
Hemingway's eldest sister Muffet, 65, is bipolar and schizophrenic. "My sister was in and out of hospitals for years," she says. "She wasn't diagnosed until she was 17 or 18. My WASPy parents would say she is going off for college and then we'd pick her up at a state hospital. I just wondered why there were bars on the window."
Hemingway also believes her late sister Margaux "suffered from bipolar disorder but was never properly diagnosed," she says. "She was diagnosed with addiction and had been drinking since she was 14." (In 1996, Margaux died from an apparent drug overdose.)
In 2014, Hemingway met Ryan Licht Sang's parents at a mental health forum in Chicago. They had been neighbors with Hemingway's father in Palm Beach, Florida, and the actress discovered she shared Ryan's birthday, furthering their strong bond. "[Hemingway's] passion to spread the word to reduce the stigma in the field of mental illness is well known, and the stories of our two families just clicked for all of us," Joyce Licht Sang tells PEOPLE.
Today, the actress, who recently wrote a book about her family's history, Out Came the Sun: Overcoming the Legacy of Mental Illness, Addiction, and Suicide in My Family, says, "If you can figure out what someone is suffering from earlier on, it would help so many families. Then you can figure out the right medication and a healthy lifestyle and hopefully save a life."