Two separate government agencies are looking into the treatment of mental health patients with severe depression at Dunedin hospital.
About 10 patients were prescribed ketamine off-label at the hospital last year.
The drug is normally used as a general anaesthetic. It is also a recreational drug, known as Special K, and used by vets as a horse tranquilliser.
Radio New Zealand's health correspondent says doctors may prescribe medicines off-label - meaning for a different use to the one for which they are licensed - if it is warranted.
No one appears to have been harmed, but the National Health Board and the Health & Disability Commissioner are looking into the case.
The Standard Nine mental health consumer group wants to know whether it was a trial and whether the patients were properly consulted.
Dunedin hospital says there was no research underway and written consent was given.
Chief medical officer Dick Bunton, says the patients were consulted and gave their consent.
Dr Bunton says the Southern District Health Board has the paperwork to prove this and it will forward that to the Health & Disability Commissioner.
Mental Health Foundation welcomes review
The Chief Executive of the Mental Health Foundation, Judy Clements welcomes the investigation of Ketamine use and is pleased the Health & Disability Commissioner is involved.
"Whatever the outcome of the investigation I think it is a timely reminder that people in our mental health care system are vulnerable, and potentially vulnerable to abuse and potentially vulnerable to neglect - and that still can be reality even though we've seen a lot of changes and improvements in the mental health system."
