Former All Black Carl Hayman is opening up on how he was “exploited” during his professional rugby career – and how his life has unravelled “in nightmarish fashion” since being diagnosed with dementia.

Hayman, aged 43, was one of the hardest men in world rugby at the height of his career, which included 45 tests for the All Blacks between 2001 and 2007.

While it was rare during his playing days for an opponent to better him in the heat of the front row, after his playing days the former giant prop has been lowered by dementia and the degenerative brain condition CTE (chronic traumatic encephalopathy).

And while headlines mainly were positive about him during his playing career, since he retired from professional rugby aged 35, headlines about him have been for all the wrong reasons: domestic violence charges against his now ex-wife which led to a suspended prison sentence in France; being dismissed as forwards coach at French club team Pau after an alleged altercation with players; and drink driving.

Now Hayman – who was once professional rugby’s highest-paid player – is set to publish a book on his on and off-field trials: Head On: An All Black’s memoir of rugby, dementia, and the hidden cost of success.

It will be published on July 5, nearly a month shy of the 22nd anniversary of him becoming the 1000th All Black when he came on as a reserve in the side’s 50-6 win over Manu Samoa at North Harbour Stadium in 2001.

“At the end of 17 years as a professional rugby player, the last eight played with the sole aim of setting up his family’s future, Hayman’s life began to unravel in nightmarish fashion,” promotional material for Head On states.

Carl Hayman is set to publish a book on his life, titled Head On. Photo / Brett Phibbs

“Head On is about the pressures on the modern athlete, where physical performance and commerce collide, and players become victims of their own success.

“Exploited then left out in the cold, Hayman is now left counting the hidden cost of the achievements that would have exceeded any young rugby player’s wildest dreams. He now fears both the known and the unknown with equal trepidation as he looks for answers to dementia and a degenerative brain condition called CTE.

“Experimental treatments, family, hope, and the enduring power of the human spirit have become Carl’s go-tos. As a relatively young man, still in his early 40s, Hayman contends with brain degeneration he should only be seeing at the end of his life, not in his prime.”

The book will cover his playing career in New Zealand, the UK and France.,

It promises “revelations about the shock All Blacks loss to France in the 2007 Rugby World Cup”, Hayman’s final test for the All Blacks was in the pulsating 20-18 quarterfinal loss to France.

All Blacks captain Richie McCaw and teammate Carl Hayman during the 2007 Rugby World Cup quarterfinal, a match that would be Hayman's last for the All Blacks. Photo / Brett Phibbs

He also opens up about his decision to quit New Zealand and take up a contract with English club, Newcastle Falcons, a decision which saw him become the world’s top-paid player.

And at a time when rugby’s relationship with booze is increasingly questioned, the book will look at “how being put on the fast track to the All Blacks as a youngster combined with the Southern Man rugby ethos in Dunedin caused him to develop a dangerous relationship with alcohol”.

Hayman is also set to talk candidly about the final stanza of his playing career, in France with glamour team Toulon.

The promotional material said he would “come to realise his European championships as captain of French club Toulon would forever be tinged with regret - all a glorious lie. Toulon had broken him.

“He was a willing participant in it, but he would soon come to realise that the glory was fleeting, and the damage permanent.

Former All Black Carl Hayman is among a group of former players trying to sue rugby authorities over head-related issues. Photo / Brett Phibbs

“This book is about the testosterone-fuelled, play-hard, drink-hard mentality of rugby, where playing with pain was not just accepted, but expected. If it took an unhealthy cocktail of painkillers and alcohol to get through to another match day, that’s what you did.”

The promotional book material says the publication is also aimed at showing “how all of us can better understand how the decisions we make can have unintended consequences, and how we can better serve our young sporting talent”.

In December 2020, Hayman and 1970s and early 1980s All Black Geoff Old told the Herald they had been in contact with British-based lawyers about their post-playing medical conditions.

Hayman initially declined offers to be tested to ascertain any damage to his brain over the course of his playing career. However, he relented after thinking of how his story could help fellow and future players.

He is now among more than 100 former rugby players who are taking legal action against World Rugby and the England and Wales rugby unions amid claims those sporting bodies failed to protect them from permanent injury relating to repeated concussions.

In October, Hayman was convicted of drink driving after being caught behind the wheel while more than four times over the legal alcohol limit.

He said he was not “in a good place” when he was pulled over by police while driving in Ōpunake, South Taranaki.

As well as suffering early onset dementia and depression, he said he was grieving the recent loss of his mother.