Customs says the number of parcels it has stopped at the border containing drugs to make fake ecstasy pills has more than quadrupled in a year.
Officers last year stopped more than 43 kilograms of analogue Class C drugs - powders that can be processed into fake ecstasy tablets.
Just 10 kilograms were seized in 2011.
The vast majority of last year's haul was found concealed in parcels at the Auckland mail centre.
Customs manager of investigations Mark Day says the drugs are imported as powder, then mixed with other chemicals to make pills purporting to be ecstasy.
He says noone knows what the makeup of the tablets is and more people are showing up in emergency departments as a result.
"Now if you're having one of those tablets it could be quite horrific, if you're having more than one of those tablets it's quite possible that you've got different chemical compositions in each tablet and therefore you're starting to get a bit of a chemical cocktail."
Mr Day says says more people are using the internet to buy the powder and Customs is stopping drugs bought from black market websites on a weekly basis.
