A mother has blamed her teenage son's secret energy drink habit for a breakdown in his mental health.
The Auckland woman said the 15-year-old told her he drank up to 16 cans of Monster Energy a day.
She said they made his anxiety and insomnia worse and his intake came to light only after he started seeing a therapist following a recent breakdown.
"I've talked to him since and his explanation is that [the energy drinks] are his best friends because when he was low he could have one of those and they'd make him feel better," said the woman, who wanted to remain anonymous to protect her son.
"The more he drank, the more he needed."
Monster has been linked to a spate of deaths in the United States.
Attempts to get comment on the mother's claims were unsuccessful, but in a statement earlier this month the Monster Beverage Corporation said eight billion cans of the drink had been "sold and safely consumed" around the world since 2002.
It said it did not believe its products were "in any way responsible" for the death of a 14-year-old American girl who allegedly died from a heart attack after two cans of the drink.
Most popular energy drinks, including Monster, contain 32mg of caffeine per 100ml.
Research quoted by the NZ Food Safety Authority says a 70kg adult can usually consume 400mg a day without adverse effects.
Lyn Gillanders of Dietitians NZ said the toxic effects of high levels of caffeine could cause anxiety and irritability.
And Elaine Rush, professor of nutrition at Auckland University of Technology, said energy drinks could intensify depression in young people.
"The problem with energy drinks and caffeine ... [is] there's a lot of things we don't know about the long-term effects ... on growth and development, particularly in children," Prof Rush said.
"We've got to be very careful."
A transtasman review of energy drinks is investigating whether caffeine levels should be cut.
New Zealand Juice and Beverage Association executive director Kerry Tyack defended the products.
Mr Tyack, whose organisation has members including V and Red Bull, said the drinks were "highly regulated" and not marketed to young people.
"They're not a product designed for children - that is unequivocally stated by the manufacturers. There are lots of products on the supermarket shelves that are not designed for children. People have to take some level of responsibility.
"The responsible producers and manufacturers have been unequivocal in their intention and their public statement that these drinks are safe, they're intended for the adult drinker and to be drunk in moderation."
The mother said therapy has helped her son improve but he still suffered from anxiety and had not returned to school.