I read Trainspotting in March 1996, three years after it was published and a month after seeing Danny Boyle’s remarkable, era-defining film at the Greenwich Picturehouse. Both experiences changed my life. In print or on screen, Trainspotting articulates the urgency of youth and defines what it means to be a rebel, a misfit or an outcast. As an outsider struggling to work out who I was and where I belonged, Trainspotting showed me that challenging the accepted order of things was not only an essential act of self-preservation, but also a means by which to understand and articulate my place in society.

Trainspotting was new and bold, a clarion call for the naysayers and nihilists who rejected the pseudo-friendly veneer of neoliberalism and embraced hedonism as a means to cope with life’s injustices. It’s about more than drugs; heroin is the MacGuffin in the story. Ultimately, it’s a tale of friendship and how people connect, bend and break along the way. Irvine Welsh uses the characters to illustrate his own world view and hold up a mirror to people on the margins of society in his native Edinburgh. Although I grew up in London and had zero interest in becoming a heroin addict, in Renton I recognised a fellow outsider. I felt seen.

Fast forward 25 years. I’m now living in Edinburgh. It’s a Sunday evening and I go to the Filmhouse with Irvine Welsh to watch Todd Haynes’ The Velvet Underground. Afterwards, I ask Irvine whether he’s ever thought about making a documentary about his life. I pitch a film to him, one that reveals a side of his character that goes beyond the public persona of a sweary hedonist speaking truth to power. Something that shows him as he’s never been seen before: a loving husband and thoughtful polymath who credits novelist Evelyn Waugh for his love of writing, and believes ‘we only learn through failure.’ Three years later, Reality Is Not Enough is the result.

From the beginning, I wanted to find an original way to tell Irvine’s story. I didn’t want it to be This Is Your Life for the chemical generation, with a bunch of talking heads chuntering on about the 90s and how Irvine’s work had inspired them. Søren Kierkegaard once mused that ‘life can only be understood backwards; but it must be lived forwards.’ The film’s editor, Angela Slaven, and I adopted this as our mantra. The quote sums up Irvine’s opposition to nostalgia; he’s not interested in looking back and chooses to focus on what’s in front of him. But I knew that observing and filming him for a year would propel him into moments of recall and reminiscence, and perhaps even the odd confession. The trick was nailing how to present that in an original and cinematic way.

While we were in Canada filming at the Toronto Book Festival, we arranged for Irvine to visit a clinic that specialises in ketamine-assisted therapy and other hallucinogenic treatments. Under close medical supervision, Irvine was given DMT, a strong psychedelic drug, and the resulting exploration of consciousness provided a framework within the film to confront the past and trigger personal reflections in the present day.

To place the audience inside Irvine’s head, we see him in a post-industrial warehouse, close to where he grew up. Within this dark inner sanctum, a white-suited Irvine literally walks through his memories, as fragments of his life and times are projected upon the walls in a Ballardian collage of flickering moving images. As the veracity of language and images collide, Irvine provides an intimate commentary on his life, work and the demons that drive his creativity. These scenes are interwoven with observational footage of him at work and play, interspersed with clips from his screen adaptations and excerpts from his novels read by Liam Neeson, Ruth Negga, Stephen Graham, Maxine Peake, Nick Cave and others.

Irvine is an adventurous and generous collaborator who empowers the people he works with by trusting their vision. In Reality Is Not Enough he delivers deeply personal reflections on the key moments that have opened his heart and soul, showing us that it’s possible to draw inspiration from the darkness within oneself and continue to evolve in defiance of the status quo. By revisiting the books, films and shows cherished and revered by people across the world, this film invites the audience to interrogate what it means to be an artist in a contemporary world where many people struggle to belong.

Reality Is Not Enough, Cameo, 20 August, 9pm; Paul Sng has donated his fee for writing this piece to Sulala Animal Rescue, an organisation that rescues stray animals in Gaza.