Rodney (not his real name), who is serving a jail term for weapons and dishonesty offences, was one of 10 men in the landmark group.
Since the drug treatment programme (DTP) began at the Otago Corrections Facility more than 950 men have graduated from the 12-week course.
Yesterday, dozens of prison staff, counsellors, ministry representatives and prisoners gathered to celebrate the occasion.
There were several speeches.
And, of course, there was a cake — baked and iced in the prison kitchen.
Corrections national commissioner Ben Clark called the drug programme "the beating heart of the prison since it was built".
Gill Hood, chief executive of CareNZ, which facilitates the programme, said it was "arguably the most successful DTP in the country".
But the most telling words came from the mouths of the men who had been through it.
Rodney said he had started out by glorifying drugs and was planning to continue on that path when he was released, until he underwent treatment.
"I’ve got a passion to live my life the way it should be now and not have a drug-fuelled maniac on the streets any more," he said.
"I’m a train off the tracks with the wheel off and you’ve helped me put the wheel back on."
Another classmate said the hard conversations had given him the "kick in the arse" he needed to confront his demons.
A third, similarly nervous about the size of the assembled crowd, quipped: "I’ve never spoken in front of this many people without a judge."
But he also had a sincere appraisal of what he had learned.
"This isn’t a magic pill that will cure your addiction, it’s a life-long process."
