The "mastermind" of a vast multi-million dollar synthetic drug dealing network says she only pleaded guilty under duress.

Fei He, a 48-year-old woman, admitted being behind an illegal "synthetic cannabis' ring run from a small Christchurch dairy during a trial at Christchurch District Court last month.

It was alleged that He and two Sockburn Dairy workers, Sui Jun Zhou, a 34-year-old real estate agent who police claimed was her armed delivery driver, and 30-year-old chef Xiwen Miao, were behind the illegal highs.

The trio pleaded guilty to charges of selling the non-approved psychoactive substances and appeared back at court today for a sentencing date to be set.

But before the court session began, He passed a typed statement to the Herald which made a series of allegations.

She claims to be the victim of police corruption in an "unjust case".

Fei He, who initially sold the highs legally over the counter, says she was a responsible seller.

"In our time, nobody has died from over (sic) the use of [synthetic] cannabis," she said.

"If we did not enter the market back in 2014, the market would be filled with dangerous products which cause death, such as those happened in late 2016. We aren't like other sellers who are in for the money – without us, the situation is much worse."

After "synthetic cannabis" boomed in popularity in 2010, and then a number of synthetic-drug related deaths, the New Zealand Government moved to ban them. It tightened the laws in 2013 and on May 1, 2014, an amendment to the Psychoactive Substances Act 2013 made it illegal to possess or supply psychoactive substances, including synthetic cannabis.

He continued to sell the drugs after they were made illegal, it was alleged.

After a police investigation, dubbed Operation Sin from April 2015 to May 2016, He was charged with possessing and supplying synthetic drugs.

A police raid alleged netted 173kg of psychoactive substances, which had a street value of $3m-$4m, the court heard earlier.

Today, He, Zhou and Miao were remanded on bail to be sentenced on November 27.

A fourth person charged with selling or supplying psychoactive substances is due back in court next Thursday.