Back in the 90s, Lanre Fehintola was a talented photojournalist who got hooked on heroin and crack while photographing addicts in Bradford. He started dealing, served time in prison, but never gave up on photography. “It saved my life,” he says in this raw, affectionate documentary directed by his friend Leo Regan from more than 25 years of footage. It’s Regan’s third film about Fehintola – and it’s easy to see what keeps him coming back. As a young man, Fehintola had such life force, such energy; a personality of extremes, he was self-destructive and sensitive, completely intoxicating.

This film begins with Fehintola in the present day, processing his recent diagnosis of lung cancer. Doctors have given him six months to live. “It is what is, Leo” he grins at the camera, charisma still cranked up past 10. Back in the 90s, the pair of them were young idealistic reportage photographers knocking around London. They took Robert Capa’s mantra to heart: “If your photos aren’t good enough, you’re not close enough.” Fehintola went back to Bradford where he grew up to photograph addicts. Naive or reckless, with no fear for his own safety, he started taking hard drugs – for research purposes, he says. “I never intended to become an addict.”

The truth feels more complicated. Fehintola was raised by strict parents; a troubled kid, he ended up in a children’s home, where he fought against racism and authority. The story of his life unfolds unfiltered. Fehintola is very good company – even when he is going cold turkey in his flat. It’s 1999 and he asks his mate Errol to keep guard while he detoxes, to stop him giving into temptation. A few days in, he’s pacing round the living room, begging to get out and score; at one point he even threatens to call the police, which has him and Errol giggling. It’s a warmer, gentler film than it sounds on paper.

• My Friend Lanre is released on 29 January in UK cinemas and on 1 February on Curzon Home Cinema.