Euthanasia advocates and legal experts say assisted suicides occur in New Zealand often and the law needs to reflect this.
Sean Davison, 50, was on trial in the High Court at Dunedin charged with attempted murder.
But after a plea deal on Wednesday, he admitted a lesser charge of assisting his mother's suicide.
Davison will be sentenced next month. He helped his mother die by giving her a glass of water containing crushed morphine tablets in 2006.
Although he takes responsibilty for giving his mother the overdose, Davison does not believe he's a criminal.
Euthanasia campaigner Lesley Martin says there needs to be legislation that could prevent people being charged when helping people commit suicide.
Criminal Barr Association president Tony Bouchier says assisted suicides are extremely common and people tend to be charged only when there is overwhelming evidence.
Mr Bouchier also says there needs to be a review of the current legislation.