Nelson Hospital is to ban diet soft drinks as well as regular soft drinks.
It follows a nationwide hospital ban on selling sugary, fizzy drinks brought in last year.
Nelson Marlborough District Health Board (NMDHB) is taking the policy one step further, removing sugar-added juices, flavoured waters, pre-packaged smoothies and even sugar-free fizzy drinks.
NMDHB chief executive Chris Fleming says diet fizzy drinks are still detrimental to teeth and health.
"Artificially-sweetened beverages may be free of calories but not of consequences," he says. "They encourage sugar craving and sugar dependence, and are strongly associated with dental erosion due to their high acidity."
From May 1, these drinks will no longer be available in Nelson Hospital cafes, shops and vending machines. Instead, patients and visitors will be offered water, milk, teas and coffee.
Nelson Marlborough was the first DHB to take sugary drinks off hospital shelves, and the Board hopes others will follow suit by removing all fizzy drinks and juices.
Professor Jim Mann, from the department of Human Nutrition and also the Department of Medicine at the University of Otago, says there are several theories behind banning diet and artificially sweetened drinks.
"The big reason for doing that is the artificially sweetened beverages are still quite acidic, so in terms of dental health they're still quite risky drinks. The argument goes it's better not to have any of them."
The other theory, that doesn't have as much evidence, is that it encourages people to have a liking and a taste for sweet things.
"If that liking for sweet things is sustained and encouraged through sweetened rather than sugary drinks, it's likely to extend into other sources of sugar," says Prof Mann.
"It's certainly not directly related to anything to do with the obesity epidemic."