Lady Gaga Says She Was Taking Lithium While Filming 'A Star Is Born'

Lady Gaga put on a brave face for the cameras while shooting "A Star Is Born" ... even as she was dealing with issues so serious she needed psychiatric medication to handle them.

The singer-songwriter discussed this difficult chapter in her life during an interview with Rolling Stone ... telling the outlet she was taking lithium -- a mood stabilizer -- while filming her Oscar-nominated turn in the 2019 film.

It's unclear why Gaga needed the medication ... but, shortly after filming wrapped, she says she had to put her "Joanne" world tour on hiatus after suffering what the magazine calls a "psychotic break."

Gaga says her sister told her she didn't even recognize her anymore ... leading to Gaga canceling the tour so she could simply focus on her own mental well-being. She says she even needed to go into a hospital to receive psychiatric care at one point.

The star explains during this period she just "crashed. It was really scary. There was a time where I didn’t think I could get better.…  I feel really lucky to be alive. I know that might sound dramatic, but we know how this can go.”