The inquest heard how Mr Erbay and his friends went to Whitianga in the days leading up to the New Year, although Sharon Harvey had raised concerns about her son's wellbeing and the company he was keeping.
Ms Harvey - whose partner, Simon Mercep, a former TVNZ journalist who now presents Morning Report for Radio New Zealand National, sat with her at the hearing - questioned some of her son's friends who were with him in the days leading up to his death.
One of those was Thomas Colbourn, who sold him a pill of mephedrone for $30 on December 30, 2010. Mephedrone is a Class-C drug similar in effect to Ecstasy.
"Cem wanted to give up drugs - did you respect his wishes?" she asked. "I would say so," came the reply.
She later tearfully asked if Mr Colbourn fully appreciated her son's state of mental health.
"You said Cem's mental health was not related to his drug use - how did you know this ?"
"I didn't," he replied.
The inquest heard how the group indulged in recreational drugs such as cannabis and Ecstasy, which some would cut into lines and snort.
Wilhelm Killip, 21, said Mr Erbay and a number of friends met at another friend's Whitianga home on New Year's Eve where the group swallowed Ecstasy and some smoked cannabis.
No one who gave evidence at the inquest could confirm seeing Mr Erbay taking the drug. Mr Killip said Mr Erbay had enjoyed a few beers, but was reserved and quiet that night.
The pair left a party on Cook Drive in Whitianga in the early hours of New Year's Day and walked back to Wharekaho Beach as they had no idea how long it would take for a taxi to arrive.
He last saw Mr Erbay as he crossed the Tohetea stream at the south end of Wharekaho Beach around 4am.
Mr Killip went back to his parents' home in Wharekaho and went to sleep in the belief that his friend had made it home safely.
Ms Harvey later asked Mr Killip how seriously he took her request that he and his mates look out for her son.
She was particularly concerned about his exposure to alcohol and drugs. "How seriously did you take these comments?" she asked.
"Pretty seriously," said Mr Killip.
The inquest heard how a barefoot Mr Erbay continued walking north from Wharekaho Beach.
He was spotted a couple of hours later at Kuaotunu beach by Kay Smith, who said he appeared healthy.
A pathologist's report showed that Mr Erbay suffered a number of injuries to his back and ribs. Those, combined with his heart condition, were the main contributors to his death.
The inquest, which is being heard before Coroner Gordon Matenga, is set down for three days.
