Countdown customers will now need to be 16 or older to purchase energy drinks in any of the supermarket's 180 stores.
Countdown's new age restriction kicks off on Monday after the move was announced in late July.
Throughout August, the company says it has been busy spreading the word about the change. Signage is now in stores to remind young shoppers they need to provide ID when buying energy drinks.
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"We have had incredible feedback from parents, teachers, health workers and our customers about our decision," says Kiri Hannifin, Countdown's general manager of corporate affairs, safety and sustainability.
"I think New Zealanders were ready for this discussion around energy drinks. There are genuine concerns out there about the impact of caffeine and sugar on our kids."
Hannifin says Countdown came to the decision after engaging with the team - many of whom are parents - as well as health and education leaders. They say communities across the board are looking to address the country's high rates of child obesity.
"Sometimes we need to step in until children are old enough to make those decisions [around sugar and caffeine] for themselves," says Dr Lane O'Sullivan, a public health advocate and supporter of the supermarket's new restrictions.
"I think reducing the access to energy drinks is a step in the right direction to helping Kiwi kids have better health outcomes."
New Zealand has the third-highest obesity rate in the OECD. Energy drinks are not recommended for children and currently require a warning on the packaging.
Hannifin says the company is aware of its other products which can also impact health when over-consumed, but says the supermarket is dedicated to introducing Health Star Ratings and reformulation.
"Countdown will continue to work on contributing to improving the overall health of New Zealanders," she says.