The founder of an Auckland drug and alcohol addiction clinic catering to the wealthy has died suddenly in the United States.

Tom Claunch co-founded the Capri Clinic in east Auckland and is thought to have helped as many as 10,000 addicts in New Zealand throughout his career.

The clinic was where Paul Holmes' daughter Millie turned to help beat her addiction issues - but the high fees of more than $15,000 were often criticised by other providers of drug treatment, as well as some of the methods used.

Mr Claunch, 73, had been suffering from health problems, and died in hospital in Alabama, where he was visiting family, before he could return to New Zealand.

Colleague Bridget Wilson said his legacy would not only be the thousands of people he treated at Capri and the now-closed Queen Mary Hospital in Hanmer Springs.

"He was training counsellors back in the 90s when there was no training there, that's a reasonably recent thing, so a lot of people in the field now owe what they have to Tom," Ms Wilson said.

Mr Claunch came to New Zealand in the 1990s from the US to work at Queen Mary Hospital which is where he met Guy Smith, an Auckland businessman who convinced him to open Capri.

Until November last year, when he went on his trip to the US, Mr Claunch was still closely involved with Capri, and Ms Wilson said his death would leave a big gap.

"No one really has the depth of knowledge or longevity that Tom had because he came from America where they had that sort of treatment for over 60 years."

Capri Clinic had received emails from people all over the world expressing their sadness over his death.

"He always had a soft spot in his heart for the still-suffering addict - and that's rare if you think how long he'd been working in 40 something years and there was nothing gone out of it at all. He was just as loving towards the people that come in here as he was on day one," she said.

Mr Claunch had battled alcoholism but had been sober for more than 40 years.

Before he came to New Zealand he worked in treatment centres in the US and Britain.

"He'd been through the mill himself, which is sign of a good operator. He knew what was going on there, he'd been through it himself."

Friends say he struggled after the death of his third wife, June, two years ago, from cancer at 51. He is survived by son Thomas Howard Claunch III, daughter Tammy Claunch Matte, and two grandchildren.