I'm guessing that word 'chemsex' is a relatively new addition to our ever-expanding language and one with which I was blissfully unfamiliar until the pre-release publicity for a documentary bearing that title landed in my inbox. Then again, the suggestion here is that unless you've been active in London's gay dating scene for the past couple of years then you'll likely also be new to the term and ignorant of its meaning. A seemingly self-evident compound word, it was actually coined to describe the practice of enhancing sexual encounters with a range of recreational drugs, including GHB, mephedrone, ketamine and crystal meth. Used in the right combination they can considerably enhance the sexual experience ("They all mean one thing," one user assures us, "It's time to party!"), but their addictively disinhibiting effect has been blamed for a worrying rise in reported cases of sexually transmitted diseases in the gay community, including HIV and hepatitis C.

It's a world William Fairman and Max Gogarty's eye-opening documentary explores from the viewpoint of those who are or have been actively involved in London's chemsex scene. Each is introduced and interviewed in a studio setting against the same red curtain background (the title montage where this process is established is a small slice of cinematic art in itself), their stories then visualised and expanded on in some startlingly frank and even intimate vérité peeks into their private lives. Overly sensitive viewers should be aware that this includes uncensored footage of shooting up drugs – known here as 'slamming' – and sexual activity, which while not exactly explicit is probably strong enough to get Daily Mail readers in a prejudicial uproar. The effect is to personalise a phenomenon that might otherwise be little more than a set of statistics or a scaremongering headline to those not part of the chemsex scene. That some of the participants choose to remain anonymous – their faces are shielded and their activities are not filmed – is hardly surprising, but the stories they tell still make a serious impression.

In a move that has faint echoes of Trainspotting, Chemsex elects not to demonise its drugs and instead allows users to outline their appeal so that we might better understand how they got hooked in the first place. "The feelings that you get," one participant reveals, "it's like a fucking firework display in your soul," while another clarifies the link between sex and drugs when he states, "When you've had that and you go back to sex when you're not on drugs, you think, 'Oh, is that it?'" The attraction of chems as gateway to sexual experimentation, meanwhile, is neatly captured by photographer Matt when he states, "You can open up receptors or areas of your mind and imagination using drugs. There's stuff that I did because I was on drugs that I've been able to do later sober. I learned how to do it whilst on drugs."

The diversity in age and background of the participants, coupled with their unflinching openness about aspects of their lives that most would prefer to keep under wraps, makes it easy for an open-minded audience to find points of identification, whatever their sexual preference or lifestyle choices. The real anchor, though, is antipodean David, who runs a London support clinic and whose level-headed evaluation of both sides of the issue and empathy for those caught up in its ultimately destructive cycle should make him the instant go-to guy for anyone looking to kick their chemsex addiction. We're well into the film before the driving force behind his commitment to the cause is revealed, which has the effect of transforming the closest the film has to a narrator/presenter into one of its principal and most positive case studies.

In common with Trainspotting, the negative effects of this hedonistic lifestyle only become clear as the film progresses. This takes many forms, from the news that five men a day are currently being diagnosed with HIV in London alone, to the all-too visible effects of drug-induced paranoia on hyperactive chemsex addict Miguel. That the lifestyle can have a communal role and offer a means of escape from isolation and prejudice is also made clear, as is the increasingly easy access to multiple partners made possible by the rise of specialist social networks like Grindr. "These days," David explains, "you come into London to find your gay life and you find Grindr. And within, perhaps, four conversations you're going to be introduced to chems. Within eight conversations on Grindr you're going to be introduced to injecting."

It's in the film's later stages that the long term effects of chemsex really hit home and we start to fear for the future of this likeable and largely upbeat group of guys who just went looking for friendship, fun and quality sex but ended up hooked on a lifestyle that could ultimately kill them. It's a message foreshadowed in the opening interview snippets when Miguel is asked why he is taking part in the film and he replies, after a suitably thoughtful pause, "I'm here because I'm alive." Yet in spite of this, the film bows out on a hopeful note for the futures of a number of those who took part, and I, for one, was cheered to think that there are people like David out there offering a strong helping hand to others looking to break that cycle of dependency. It's an upbeat parting message from a revealing, moving and refreshingly sensation-free documentary that deserves to be far more widely seen that it probably will be. Catch it while you can and help spread the word.