Anorexia has long been a controversial subject for film and TV with dramas such as Netflix’s To The Bone attracting a wave of negative attention. Now BBC3 aims to counterbalance those negative headlines with Overshadowed, which mimics the feel of confessional YouTube video diaries to paint a devastating, realistic picture of the way in which the illness can take hold.

The drama series was produced by Rollem, the company set up by screenwriter Kay Mellor, and written by Irish newcomers Eva O’Connor and Hildegard Ryan. Mellor became involved as executive producer after watching O’Connor’s play, Overshadowed and directed by Ryan, in Dublin.

“I’ve been interested in body image for a long time and when I watched [the play] Overshadowed it seemed as though I was learning things about anorexia that I didn’t know before,” Mellor says. “I realised it might work on TV.”

The TV version of Overshadowed comprises eight 10-minute episodes, and tells the story of Imogene (Michelle Fox), a gawky and enthusiastic teenager who starts up her own video blog, an upbeat mixture of tips, advice and light-hearted personal confessions. But beneath Imogene’s cheery facade things aren’t so straightforward: she’s made a new friend in Anna (O’Connor) who tells her that the only way to become perfect is to exercise more and eat less.

The decision to personify Imogene’s anorexia, portraying it as a devil on the shoulder whispering bad advice, was based on O’Connor’s own lengthy experience with an eating disorder.

“What I wanted to make clear is that anorexia is a mental illness and it’s relentless. It’s with you every minute of the day,” she says. “When somebody has an eating disorder they can be really difficult to live with. They can be cruel and reckless and self-destructive.

“One of the things I wanted to say with Overshadowed is that it’s not the person that’s like that, it’s the thing living inside them. On my first day in therapy my therapist said, ‘imagine it like a creepy demon living in your biscuit cupboard’. That’s how the character was born.”

They chose the 10-minute format and filmed from Imogene’s perspective to mimic the setup of YouTube’s streaming videos, says Ryan. It allows Overshadowed to reflect on how today’s teenagers watch content and comment on the way social media allows us to present our “best selves” to the world.

“When I look at Instagram or Twitter, I’m always struck by the difference between the image and the reality,” says Fox. “Everyone posts the life they want you to see but what happens when that image becomes impossible to sustain?”

O’Connor and Ryan didn’t want Overshadowed to fall prey to the issues that have affected previous anorexia dramas. Fox didn’t lose weight for the role and the progression of Imogene’s illness is instead suggested by clever make-up and wardrobe choices.

“One of the biggest problems I have is when films or TV shows just make the person look thinner but still looking great. It brings a morbid fascination to the idea of eating disorders and that’s not what we were aiming for,” she says.

Yet it is also not without hope. “The power is that you see her getting worse and worse but you also see her find her resilient self as well,” says Ryan.

For O’Connor, playing the monster was ultimately an empowering experience. “I never wanted to play somebody with an eating disorder but I did want to talk about it,” she says. “Playing Anna is almost like my final two fingers to anorexia, like ‘ha, ha, I’m embodying you on screen now bitch.’ There’s something that’s really fun about that.”

Overshadowed is on BBC3 from October