Terry Kupers can’t sleep. The veteran psychiatrist, author and solitary confinement expert, 81 and still working on multiple projects, is particularly troubled by the brutal spate of Immigration and Customs Enforcement (Ice) raids rocking communities around the US.

“My father came from Russia, so I’m an immigrant’s son,” he said. “I can’t live with these raids. I need to do something about it.”

Recently, “doing something” has meant putting the finishing touches on a new book, Ending Isolation: The Case Against Solitary Confinement, which Kupers co-authored with three others.

Out on 4 September from Pluto Press, the book is an exhaustively researched takedown of solitary confinement: the practice of isolating an incarcerated person for hours, days, weeks or even years in a cell all their own. It’s a practice long decried by experts including Kupers, but despite their repeated warnings, researchers and advocates generally agree that anywhere between 75,000 and 80,000 people are locked in solitary confinement in the US on any given day. The true number could be much higher, and as the book points out, “there is no evidence that solitary confinement actually reduces violence. Instead, there are research findings that point strongly to the opposite conclusion, that solitary confinement worsens the problem of violence, both within prisons and in the public.”

Considering this, Ending Isolation is a vital, systematic dismantling of every possible argument one could use to justify solitary confinement. The book covers everything from the history of solitary, the disturbing overlaps between sexual assault and isolation practices, and a deep dive into who gets “sent to the hole” (spoiler alert: it can be any prisoner at any time for the vaguest reasons that more than often defy logic).

The chapters feature narratives from people who have lived through torturous isolation, which makes for a mentally fraying read that feels, at times, like you’re peeking behind a curtain in a room where you’re not meant to be.

“Most people who go to solitary confinement are broken by the experience,” Kupers said in an interview with the Guardian. “They have what I’ve termed the decimation of life skills. They become unlearned in terms of how to relate to others, and in terms of the prison environment, they then get into more trouble when they get out of segregation.”

Kupers’ insights are based on decades of interviews with people who have experienced solitary confinement in America’s prisons. His latest book offers the in-depth psychiatric research Kupers has previously delivered in five other books and hundreds of articles – only this time he’s joined by three co-authors, including two people who are currently incarcerated.

Chris Blackwell, an award-winning journalist currently serving a decades-long sentence in Washington, kicks off the book with an engaging prologue recounting how he endured his first stint in solitary confinement at the age of 12. The experience “solidified my distrust for authority figures forever and drove me into a deep hate for ‘the system’”.

He has now spent most of his life as part of that system. By age 18, he’d been arrested more than 20 times. After killing a man during a drug-related robbery (“an act I would never be able to repair”, he writes) Blackwell received the 45-year sentence he is currently serving. More solitary confinement awaited, too.

“Nothing is worse than becoming a target in prison,” he writes in the prologue. “I refused to comply with what I felt was a constant abuse of power, and guards refused to allow me to rebel without punishment for my actions.”

Even after years in isolation, Blackwell says he is still struggling to understand the impact those experiences had on him. But he knows the good he offers – his writing, his advocacy – is in spite of solitary confinement.

Kupers says Blackwell is representative of a large proportion of prisoners: “He didn’t have murder in his mind,” but he committed a terrible crime that will haunt him – and others – for the rest of their lives. When they started working together on this book, Kupers realized that if circumstances were different, he and Blackwell would have been close friends. He admires his intellect, the grassroots organization Blackwell helped co-found from behind bars, and the harrowing essays and incarceration accounts Blackwell has published in the Appeal, the New York Times, the Washington Post and many other outlets.

“He happens to be behind bars and therefore his life is very limited and restricted,” Kupers said. “But it’s amazing what he’s done given those limits.”

It was Blackwell who recruited Kupers to co-author the book alongside himself and Deborah Zalesne, a law professor at the City University of New York. Together, Blackwell and Zalesne had the personal testimonies and legal foundation covered; they needed Kupers to add the mental health angle. He does so convincingly, detailing how solitary confinement, especially when it’s prolonged, can cause severe anxiety, panic, sleep problems, psychotic behavior and severe post-traumatic stress disorder. Many people “sent to the hole” develop a compulsion for self-harm, and Kupers says this shouldn’t surprise anyone.

“Prolonged solitary confinement is torture,” he writes.

These repeated insights, while necessary, aren’t the main draw of the book. Rather, it’s the contributions of people such as Kwaneta Harris, Ending Isolation’s fourth and final co-author.

Harris is an incarcerated writer whose work has helped shed light on the crisis of sexual assault in prisons.

“I used to think there was a timeline for when people lost their minds in solitary confinement. Six months, two years, maybe five. I was wrong. The descent into madness doesn’t follow a schedule. Even now, back in medium-security, I wake up some mornings thinking I’m still in that cell,” she writes.

Those passages, coupled with reams of research, leave no doubt that solitary confinement constitutes cruel and unusual punishment. The question, then, is if the practice will ever end.

“There’s a split in correctional authorities,” Kupers said. “Probably around half think that solitary confinement is a very bad idea.”

In Donald Trump’s second term, Kupers is concerned about the advent of places like Alligator Alcatraz.

“This book is representative of this finding that ending solitary confinement is strategically extremely important in the context of what Ice is doing, for instance, and the emergence of a police state,” Kupers said. “If we required that people who are behind bars are entitled to the civil and human rights, which they are by law entitled to, if we gave them those rights, including due process, that would massively change what’s going on right now.”

Kupers adds: “If we continue to treat people like monsters, that is exactly what they will become.”

• Ending Isolation: The Case Against Solitary Confinement comes out on 4 September from Pluto Press. The book’s release date coincides with the launch of a nationwide bus tour hosted by Unlock the Box.