When John Davidson was 10 years old, he experienced his first symptoms of Tourette syndrome – small facial tics and eye blinking.

By the time he was 13, the neurological condition was causing full-body movements so extreme he compares himself with the young heroine in horror film The Exorcist.

John tells Sky News: “There’s a scene where the girl’s on the bed and her whole body’s twitching about and screaming. That’s almost what it felt like. My tics became so extreme that I was hurting myself. I was pulling muscles. I was tired all the time.

“I would break down and cry so many times in a day because I was totally out of control. Something had completely taken over my mind and my body.”

Growing up in Galashiels in the Scottish Borders, John was repeatedly told his symptoms were in his head – or worse, intentional – when a chance meeting with a visiting junior doctor while in hospital led to a diagnosis.

Largely unheard of in the 1980s, today, high-profile figures including Scottish musician Lewis Capaldi and US star Billie Eilish have publicly spoken about living with Tourette’s.

Affecting more than 300,000 people in Britain, it’s more common than many think. One schoolchild in every hundred is estimated to be affected by the syndrome, according to NHS England.

While severity can range, there is currently no cure.

And while the University of Nottingham is working on a device which uses electrical pulses to suppress tic urges, the wristband – called Neupulse – is currently awaiting full medical approval.

‘Medication turned me into a zombie’

Treated with drugs as a child, John suffered devastating side-effects: “Anti-psychotic medications turned me into a zombie. I’ve got probably about a two-year period in my teens where I have no real proper memories.”

Frustrated by the lack of support available to him growing up, John is now a Tourette syndrome campaigner, recognised for his work with an MBE.

But even that came with challenges unique to his condition. At the 2019 ceremony at Holyrood Palace, when collecting his award, John shouted “F*** the Queen” at Elizabeth II.

He says: “It was horrific for me. It was like the last thing I ever wanted to have to shout. And I think that’s the nature of the coprolalia, part of the condition, where it’s the worst possible thing you could say in that situation.”

Affecting a minority of the Tourette’s population, coprolalia is the involuntary utterance of socially inappropriate words or phrases.

While less common, it’s the feature of Tourette’s most often portrayed in the media.

John goes on: “It came as much of a shock to me as to everyone else, you know? But I’m the one in the moment having to deal with those emotions and feelings of wanting the ground to swallow me up. [Thinking] I don’t want to be here any more.”

‘Living with it is absolutely awful’

Now, in a bid to tackle the stereotype, a film is being made about John’s life based on his 2025 memoir, with Game Of Thrones star Robert Aramayo playing the lead role.

No stranger to media exposure himself, John has appeared in numerous documentaries over the years, following on from the groundbreaking 1989 documentary about his life, John’s Not Mad. But it hasn’t always been a positive experience.

John says: “Every time they make a documentary, they make such a thing about the swearing part, which then stigmatises the condition because people are then left to assume that everyone with Tourette’s swears and shouts obscenities.”

In reality, coprolalia is not typical of the condition and only affects around one in 10 people with Tourette’s.

John acknowledges there is a comedic element to this: “When people think of uncontrollably swearing like that, it’s funny. ‘Oh my God’, you know, ‘shock, horror’. But for the one living with it, it’s absolutely awful.”

‘Let’s have sex!’

It’s a sentiment the film’s director echoes.

Kirk Jones first met John in 2022. Meeting him at his house to discuss the potential of making the film, John opened the door and, after inviting him in, shouted in his face: “Let’s have sex!”

His first introduction to John’s verbal ticks, the director admits it was a “steep learning curve”.

He tells Sky News: “There’s something about Tourette’s, which I don’t think has made it a very friendly or accessible condition. I think that’s down to the fact that people who have coprolalia come across as being aggressive or argumentative or difficult or upsetting people, and I think that’s unfair. They need as much support as anyone else.”

The director says it took him some time to gain John’s trust, showing he wanted to do more than just revisit tired stereotypes.

He says: “The Tourette’s community had been kind of abused in the past. They’ve been invited to appear on TV shows or radio or be in newspaper articles, under the guise of helping people to understand Tourette’s more. But what the TV channel or the radio show really wanted was just a cheap laugh.

“When I first met John and started talking about the idea of the film, he was understandably suspicious.”

Handing over some creative control, John is also an executive producer on the film.

‘When you laugh, it breaks the ice’

Now, at 54, and having lived with the condition for over 40 years, John believes people are becoming more tolerant of Tourette’s, but would love to see further acceptance.

“It’s about not being shocked. It’s not about being dead serious with a straight face. Feel free to laugh, because when you laugh, it breaks the ice.

“I wish people had the confidence to approach people with Tourette’s and just deal with it as if it was an everyday thing.”

The director, too, hopes the film will have a real-world impact and open people’s eyes to the reality of the condition.

He says: “I hope this film can play a small part in starting to refocus people’s attention on helping and supporting people rather than just laughing or mocking.”

I Swear is in UK and Irish cinemas from Friday 10 October.

Anyone looking for support or information about Tourette syndrome can access resources at Tourettes Action or Tourette Scotland for those living in Scotland.