Dreyfuss, 66, first spoke publicly about his disorder in the 2006 documentary The Secret Life of the Manic Depressive. Since then, he's been sharing his personal struggles at conferences around the country to elevate the discussion on depression.
"There's no shame in having depression," Dreyfuss told PEOPLE at Thursday's Hope for Depression Research Foundation luncheon in New York City. "By telling my own story, I hope to help remove the stigma. It never should be something to hide."
At the luncheon, the actor spoke candidly about his manic depression, which has tormented him for much of his life. One symptom he's battled with is anxiety.
"I trembled in fear. It's like the night before the test and you aren't really sure about the subject and this balloon of self-loathing starts to swell up fast in anticipation of failure," he said. "I lived that feeling everyday, every minute for my entire life."
Starting at the age of 14, Dreyfuss realized he was living with a roller coaster of emotions – he'd have lots of energy and feel great, then suddenly feel down or anxious. During his happy days, "I was thrilled with my life entirely too much," he said.
As an actor, Dreyfuss was on top. At the age of 30, he won the Best Actor Oscar for 1977's The Goodbye Girl. "I enjoyed turning down work as much as I enjoyed getting the job," he said. "I was living from thrill to thrill and nothing bad happened to me."
But the good times didn't last. While shooting the 1991 romantic comedy Once Around with Holly Hunter, his mood swings and lack of self-esteem started to affect his work. "Had I not been depressed, I would have given a very different performance," he said.
How Counseling HelpedThat was the beginning of his growing self-hatred. By 1995 his marriage to writer-producer Jeramie Rain ended in divorce. She took his three children and moved out.
"I needed help. I didn't want to lose my children," he said. "I felt divorce was a valid reason for being depressed, but I didn't know it would last as long as it lasted."
Despite his serious sadness, Dreyfuss chose not to end his life for the sake of his children: "I would have never committed suicide because my daughter would have been really pissed. I wouldn't want to hurt her. When you have a kid, no matter how much success or money you have, you have this love that is beyond the bounds and you would take a bullet for your child. So I didn't want to cause them any pain."
He began seeing a therapist and received treatment for his bipolar disorder. "Counseling helped kill my guilt," he said. "We went on a journey to find the right meds and it took four long years."
Dreyfuss was prescribed Lithium, which helped control his depression. He's now using a different drug – which he won't name – and it's allowing him to live his life as himself.
"I'm able to be Richard again," he said. "Things are great."