When Johann Hari was 18 he took his first antidepressant. That morning he had visited a doctor and explained how, ever since he was small, he had battled with feelings of overwhelming sadness. When he wasn’t taking himself off to cry quietly, an anxious monologue would be running in his head. “Get over it,” it would say, “stop being so weak.” The doctor was reassuring, explaining that these feelings were to be expected since Hari was one of many people whose brain had depleted levels of serotonin. And so he prescribed some pills that would restore the balance. As Hari swallowed his first tablet, he says, “it felt like a chemical kiss”.

It wasn’t until he was in his 30s that he thought of all the questions the doctor didn’t ask, such as: what was his life like? What was making him sad? What changes could be made to make life more tolerable? The push and pull between “reactive” depression (the kind that relates to our environment and life experience) and “endogenous” depression (where something goes wrong in the brain) forms the basis of Lost Connections, an eye-opening, highly detailed though sometimes frustrating investigation into the causes and cures of depression.

The book is part personal odyssey, in which Hari gets to grips with the flaws in his own treatment, and part scholarly reflection, where he sifts through the varying perspectives of scientists, psychologists and people with depression. In the first half, he examines the social and psychological factors that can cause reactive depression, which include hardship, trauma, loneliness, lack of fulfilment, absence of status and disconnection from nature. He casts a damning eye on the research practices of the pharmaceutical industry, which has a clear investment in the endogenous argument, and deftly debunks the popular notion that depression stems from faulty genes.

It’s no surprise that Hari is meticulous in revealing his methods, given his past misdemeanours while working at the Independent. In 2011 it emerged that he had been using quotes from his interviewees’ books, and from previous press interviews, as if they had been given to him. Thus there are copious notes at the back of Lost Connections containing websites, journals and books consulted, while his interview recordings have been made available online.

As well as sifting through hundreds of academic papers, Hari has talked directly to people who have made great strides in understanding depression. He meets a junkie-turned-neuroscientist in Sydney, climbs a mountain with a primatologist outside Banff in Canada, visits a rehabilitation centre for gaming addicts in Washington state and observes an Amish community in Indiana. So it’s somewhat baffling, given the legwork put in, how little his interviewees actually get to say. In London he meets George Brown and Tirril Harris, authors of a groundbreaking study of the social causes of depression that saw them going into the community and interviewing women about their lives. He makes clear the importance of their work and spends 10 pages telling their story, but quotes just a few sentences from each. It’s a recurring theme: Hari crisscrosses the globe to meet prominent thinkers only to tell their stories on their behalf, throwing in a couple of quotes if they are lucky. (He does, at least, give his case studies a louder voice; his conversations with those dealing with depression are extremely moving.)

Elsewhere, the prose suffers from Hari’s tendency to underestimate the reader’s capacity to comprehend digestible concepts, leading to some overwrought metaphors and flashes of daft melodrama. At one stage the chemical imbalance theory lies “broken on the floor, like a neurochemical Humpty Dumpty with a very sad smile”.

The research is thorough, however, and his ability to locate a narrative in what one might fairly assume to be bone-dry source material is undeniable. The lazy, oversimplified and unimaginative attitudes of the medical establishment to anxiety and depression laid out here beggar belief. You could argue that finding fault in the current system isn’t that hard – it’s the solutions that present the real challenge. But Hari is clear about the difficulties of the task ahead and, in offering new ways of thinking, presents not surefire solutions, but, he says, “an alternative direction of travel … points on a compass”. Put in the broadest terms, his argument is that if our current malaise lies in disconnection from vital human requirements such as neighbourliness, professional fulfilment, acknowledgment of trauma and so on, then we need to find ways to reconnect.

Hari is by no means the first writer to call for a compassionate, common-sense approach to depression and anxiety, or to point out how medical and societal attitudes have fallen short. But his book brings with it an urgency and rigour that will, with luck, encourage the authorities to sit up and take note.

• Lost Connections: Uncovering the Real Causes of Depression and the Unexpected Solutions is published by Bloomsbury. To order a copy for £12.49 (RRP £16.99) go to bookshop.theguardian.com or call 0330 333 6846. Free UK p&p over £10, online orders only. Phone orders min p&p of £1.99.

If you are affected by depression or suicidal thoughts, there are places you can turn to. In the UK, Samaritans can be contacted on 116 123. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. In Australia, the crisis support service Lifeline is on 13 11 14. Other international suicide helplines can be found at www.befrienders.org.

• Note by readers’ editor, Paul Chadwick, added 7 February 2018: After publication, I considered a complaint relating to Guardian and Observer coverage of the book: an extract; Q&A with the author; this review; blogpost on 8 January; and blogpost on 24 January. I concluded that the book’s author, Johann Hari, and his critic in the blogposts, Dean Burnett, were entitled to their differing views, and that the Guardian and Observer editorial standards had been met. Due to the sensitivity of the issue involved - namely, the causes and treatment of mental illness - I also concluded that it was appropriate to emphasise for readers that the author and his critic have both expressed the view that people taking anti-depressants should not stop taking their medication abruptly or without seeking professional advice.