The man behind a letter asking hundreds of recipients to try the drug P has defended the stunt, saying it was designed to shock people into action.

Marco Marinkovich, executive director of agency CreativeBank, which sent the letter, said it "backfired" on seven or eight but had a "huge positive impact on the rest".

"What I wanted was for people to experience the initial shock of going 'What the hell is this'?" he said. "I was emailed by a number of clients saying 'Thanks very much I will raise it with my kids over Christmas' and stuff like that."

He said about 25 companies had responded, asking how they could help.

"It's such a new area nobody knows how to deal with it. Nobody knows the right education and what to do."

One recipient contacted the Herald "disgusted" at the prank and said he would no longer work with CreativeBank.

Each purposely misspelled letter contained a little bag of rock salt and said: "Don't know if u ever tried P before but lots of kiwis have and they cant get enough of it. its such awesomely mindblowing stuff." It then invited the reader to log onto their own private section of a P Free NZ website.

Mr Marinkovich gave the Herald a dummy login name, revealing a personalised page with a letter warning of the dangers of the drug, a video clip with graphic images played to an addict's poem and other facts.

The letter began: "The little bag of crystals you've been holding is rock salt, not P. But when a bag of P as small as this can sell for around $1000, it's easy to see why a drug so addictive causes so much violence and crime. Sadly, for many kids, this drug will see they get quite the wrong kind of 'Christmas bash'."

The Christmas letters were sent in support of the Stellar Trust's anti-P campaign, which Mr Marinkovich said he helped kick off.