Pillows designed to alleviate ailments are aggravating neck-pain issues for some customers.
Sellers of bamboo pillows claim the products ease nerve pressure, support the neck and stop snoring.
But a health professional has said some people's conditions are worsening after using them.
New Zealand Chiropractors' Association vice-president Dr Hayden Thomas is aware of users of bamboo pillows who have experienced problems.
"What we've found with the bamboo pillows specifically is that some people find it sometimes forces their spine into a position they're not quite ready for, and that can aggravate symptoms with neck pain and stiffness and sometimes headaches."
However he also said people using bamboo pillows should continue to do so if they feel they work for them.
"On the other side of that I've had some people who it's been really good for.
"It's like any kind of device or support, some people it suits and some people it doesn't."
Dr Thomas said neck pain is a complex issue, and it involves numerous factors.
"I guess the good thing with the money-back guarantee is that people can give it a try, but I'd say a lot of people should not expect the pillow to be the whole answer."