Channel 4 has ordered a new 6-part comedy drama about a young woman with a mental illness.

Pure will follow Marnie, a 22 year-old who runs away to London to discover herself, having developed a severe - and undiagnosed - form of the mental condition obsessive compulsive disorder.

The channel explains: "22 year old Marnie is not OK. She may just seem quiet to others, but the noise inside her head is relentless. For the last 2031 days, she has been assailed by an incessant barrage of graphic x-rated thoughts that intrude, at the most inopportune of moments, on her day to day life. Whether she's sitting exams at university, waiting at a bus stop or passing strangers on a street, her life is interrupted by irrepressible sexual thoughts. Marnie has no idea what's wrong with her - Is she gay? A sex addict?? A pervert??? Why is she plagued by these mental images and what do they mean? Is that who she really is, deep down?"

The series has been written by Kirstie Swain, based on the real memoir of author, campaigner and journalist Rose Bretécher (pictured), and will begin filming early in 2018 for broadcast later in the year. No casting has yet been confirmed, and the show will be produced by Drama Republic; some of the team behind My Mad Fat Diary.

Producers add: "Now in her final year at university in Scotland, Marnie's anxiety has reached fever pitch. At breaking point, she packs a bag, jumps on the first available train and, unable to go home, ends up in London. She doesn't know a soul, not even herself. But the big city is the perfect place to reinvent yourself, right?

"Let loose in London, Marnie experiences the wonder and terror of the city unfolding itself before her; rooftop parties, impossibly crowded tubes, and midnight adventures. She soon finds out she's not the only one who's lost, however, as she meets a host of other characters who alternatively help and hinder her during her unique journey to find her real self.

"Unbeknownst to Marnie as she embarks on this journey of self-discovery, she's actually caught in the grip of an excruciating form of obsessive compulsive disorder - nicknamed 'pure O' - where her obsessions take the form of intrusive thoughts, often sexual, and the compulsions are unseen mental rituals that deeply affect her daily life and her relationships."

Channel 4 conclude: "It is a moving, warm and truthful exploration of one young woman's search for herself and her very real struggle with mental illness. It explores what it means to be a young woman today, what it means to discover a whole new world. It's about finding new friends, and most importantly, about falling in love."

Rose Bretécher says: "When I wrote my memoir, Pure, my mental health condition was virtually unheard of, and my thoughts were deeply taboo. Now, to collaborate on its adaptation with such a talented, diligent, witty team, is an extraordinary validation and privilege. As my story is reimagined on-screen, we have a unique opportunity to reach untold thousands of people who have lived for years, as I did, in secrecy and shame. To humanise their darkest experiences, to empower them to change, and to give them new hope."

Kirstie Swain, writer, says: "I've always been an obsessive-worrier and over-thinker...or maybe it's the other way round. It runs through me like a stick of rock. While I don't suffer from Rose's exact condition, Pure resonated so deeply with me because I can absolutely relate to the experience of being an outer calm and an inner cyclone. I'm so glad to be making this show with Drama Republic and Channel 4. It embodies everything I want to say as a woman and as a writer and it gives voice to the often silent issue of mental health."

Beth Willis, Head of Drama at Channel 4, says: "Kirstie's scripts truly crackle with her searingly honest portrayal of the high points and horrors of being young. They are endlessly witty, wise and wonderful. We are so thrilled that she and the brilliant producers of My Mad Fat Diary will soon be landing on Channel 4."

Roanna Benn, Executive Producer for Drama Republic, adds: "We are so thrilled that Rose has entrusted her deeply personal, brave and wonderfully candid memoir to us. And we couldn't be prouder that this will be screenwriter Kirstie Swain's first original series. Kirstie is a fearless writer: funny, idiosyncratic and deep! At Drama Republic we love bold and extraordinary female protagonists and Pure will feature one like no other. We hope that Marnie will burst onto our screens and into our audience's hearts like she has ours."

The series will be on air late in 2018.