For the first time, actress Hayden Panettiere is opening up about her struggles with addiction, postpartum depression, and motherhood. In an interview with PEOPLE, she says her addiction nearly cost her career and her life.

"I was on top of the world and I ruined it," the former child star and Nashville actress says. "I'd think I hit rock bottom, but then there's that trap door that opens."

Heartbreakingly, Hayden Panettiere's substance abuse began when she was still a child—and she had no consent over it. She tells PEOPLE that someone on her team began offering her "happy pills" before she walked red carpets at just 15 years old.

"They were to make me peppy during interviews," she says. "I had no idea that this was not an appropriate thing, or what door that would open for me when it came to my addiction."

While her career took off with shows like Heroes and Nashville, Panettiere was using opioids and drinking regularly.

Related: My baby was born addicted to heroin. Here’s how I forgave her birth mom.

"My saving grace is that I couldn't be messy while on set and working," she says. "But things kept getting out of control [off set]. And as I got older, the drugs and alcohol became something I almost couldn't live without."

Panettiere had been dating world heavyweight boxing champion Wladimir Klitschko in 2009, and the pair became engaged in 2013. They welcomed daughter Kaya in 2014, which led to a severe case of postpartum depression. She says she refrained from drinking or using drugs while pregnant, but soon fell off the wagon after Kaya's birth.

Panettiere sought treatment for her depression, but still found herself struggling — and increasingly independent on alcohol to get through the day.

"I never had the feeling that I wanted to harm my child, but I didn't want to spend any time with her," Panettiere says. "There was just this gray color in my life."

Related: Getting sober saved my motherhood (and my life)

Soon her relationship with Klitschko began to crumble, and her dependency on alcohol deepened. After her series, Nashville, ended, she was at her lowest point. She made the devastating decision to send Kaya to live with her dad in Ukraine after the pair split up.

"I would have the shakes when I woke up and could only function with sipping alcohol," she says. "It was the hardest thing I ever had to do. But I wanted to be a good mom to her—and sometimes that means letting them go."

The Substance Abuse and Mental Health Services Administration (SAMHSA) has reported that nearly 15 percent of women within the first year of birthing their child with postpartum depression engaged in binge drinking. Nearly nine percent of this group reported abusing other drugs. These prevalence rates are higher than with women who did not give birth and those who did give birth but did not have postpartum depression.

Unfortunately, the American Addiction Centers say there is still a lack of research into the connection and causal relationship between substance abuse disorders and postpartum depression.

Related: Co-parenting with an addict means I am basically raising my son alone

After being hospitalized with jaundice from her alcoholism, Panettiere made the decision to get sober. She entered a rehabilitation center for eight months to help her with her addiction. She tells PEOPLE she's grateful that she's "part of this world" again, and checks in with herself all the time. She's back on set, reprising her role as Kirby Reed in the next Scream film, and has been working with Hoplon International, the charity she founded in March that raises funds for Ukraine.

"This hasn't been easy and there were a lot of ups and downs," says Panettiere of her journey to sobriety and happiness. "But I don't regret even the ugliest things that have happened to me. I feel incredibly accomplished. And I feel like I have a second chance."