An Auckland advertising agency has apologised for sending a letter to hundreds of people, including Prime Minister John Key, inviting them to try the drug P.

Attached to each letter was a bag of rock salt.

The agency, CreativeBank, said it was acting in support of the Stellar Trust and its anti-drug campaign.

Its letter, crudely written and purposely misspelled, said: "don't know if u ever tried P before but lots of Kiwis have and they cant get enough of it. its such awesomly mind-blowing stuff!".

The recipients were invited to check out their own private area located on a website. The letter then said: "ps I got ur name from the guys at creativebank, their into P and looking 4 people to join them". Alongside the bag of salt was a scrawled note: "On the street this much P is worth $1000!!". Some letters had a personal message.

CreativeBank executive director Marco Marinkovich could not be reached yesterday, but said in an apology email that the letter was designed to shock. "The intent to shock was deliberate and has reacted badly on 7 of the 241 people we sent this card containing rock salt to," he wrote.

One recipient, who did not want to be named, said: "It's one thing to have a charity and try to push what he's trying to push but that's disgusting."

The man said his firm would no longer be dealing with CreativeBank and had filed a complaint with police.

In his apology, Mr Marinkovich said the letter was sent to support the Stellar Trust's campaign, A P Free New Zealand.

"I thought with the (website) and mentioning CreativeBank our clients in particular would have expected it to be us."

He also gave the mailing list to police "so that if people called, their fears could be put to rest".

"For the distress I caused those people I have spoken to them and apologised," Mr Marinkovich said. "But I don't think that comes anywhere close to the living hell addicts and their families find themselves in on a daily basis," he wrote.

The Herald was unable to access the named website last night.