Depicting mental illness on screen can be a perilous business. Glenn Close's borderline personality disorder in Fatal Attraction was whittled down to her dangerous character being slammed as a 'bunny boiler' while Netflix teen drama 13 Reasons Why was slaughtered in the media where its portrayal of depression and suicide was deemed to be glamorous. In new six-part Channel 4 comedy-drama Pure, there's very little that's attractive or simplified about the particular type of OCD experienced by main character Marnie.

Played brilliantly with a witty desperation by newcomer Charly Clive (her note-perfect Scottish accent is especially impressive given that she was born and raised in Oxford), Marnie suffers from Pure O, an obsessive strain which leads her mind to be assaulted by sexual thoughts and degrading imagery at the most inconvenient of moments. She will be chatting to a GP one minute and then in a flash be plagued with an image of the doc licking her own armpit; as she gives an unfortunate speech at her parents' anniversary party, an orgy breaks out in Marnie's brain, with her mum and dad and assorted guests getting down and very dirty.

All of these scenes are played out in front of us, and while it's all deeply sexual, there's little here that anyone should be titillated by. The quickly edited erotica is exhibited as it is meant to be: horrific, distracting and invasive. While Marnie should be a mess, she stumbles through life making one faux pas after another, always expecting her demons to push all sensible, sociable thoughts out of the way in order to let the carnage and carnality seep in.

But there might be some hope for her. She befriends Charlie (the equally superb Joe Cole) at a meeting for sex addicts (at this point Marnie hasn't got a name for what she's going through), and they embark on a relationship that could amount to a mutual shoulder to cry on or might veer towards something a bit more destructive. Meanwhile she stumbles into an internship at an online magazine and just about manages not to upset everyone there with her seemingly unhinged manner, until, of course, when she finally does.

Marnie's difficulties are far from the stuff of humour (Pure is adapted from a traumatic memoir by Rose Cartwright), even though the tone is often light and frivolous. It's this clashing of moods within the programme that keeps it from tipping into either regrettable farce or full-blown tragedy. There are small tragedies and farcical scenarios aplenty, but they all add up to a funny, frank and non-exploitative portrayal of an inner world that's permanently on high alert.

Episodes watched: 3 of 6

Pure is weekly on Channel 4 from Wednesday 30 January, 10pm. All episodes are available on All 4 at 10.30pm.