The Waikato District Health Board (DHB) is investigating reports of a doctor arriving at work drunk and abusing at least one patient.
The doctor reportedly arrived in a patient's room about 4am yesterday and began calling the man derogatory names.
The DHB's chief executive, Dr Nigel Murray, said it took the allegations very seriously.
The staff member had been spoken to and was now on leave, he said.
"We will be investigating the circumstances surrounding this incident so we can take the appropriate action and offer the necessary support.
"We would also encourage the patient to talk to us in confidence about this serious complaint, which will help us complete our investigation."