The Medical Council has decided to deregister a methamphetamine-smoking Northland doctor who was sacked for prescribing controlled drugs to her partner and others.

The council has now published its decision after the doctor, Lynda Marie Emmerson, lost an appeal in the High Court against an earlier ruling of the Medical Council's professional conduct committee (PCC) that recommended her registration be cancelled.

Emmerson was working at Whangārei Hospital's Tumanako mental health unit as a psychiatric registrar when she prescribed controlled drugs - morphine, diazepam, dihydrocodeine tartrate, amoxicillin and tramadol - to her partner, who was not a patient.

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She also wrote prescriptions for her partner's mother and a colleague.

Northland District Health Board complained to the council about her conduct and the matter was referred by the council to the PCC in 2015.

The DHB recorded nursing staff as saying Emmerson had told them she would, if tested, fail a urine test for abuse of different substances.

The PCC engaged another doctor to establish whether Emmerson had a substance-related disorder or a mental health issue.

She told the doctor that from 2013, she smoked small amounts of meth at four or six weekly intervals, but only on weekends, and last used it during Easter in 2015.

The drug, she said, boosted her energy levels, and she used it only when she had four days off work. Emmerson also used cannabis, but would stop if she returned to work. She tested negative for meth but positive for cannabis in a drug test in June 2015.

The tribunal said Emmerson had not only "demonstrated an acute lack of judgment" but also "an irresponsible attitude to complying with her professional obligations, the criminal law and the duty of candour which she owes to her professional organisation".

It said her conduct jeopardised the safety of patients she had prescribed drugs to, patients in her ward and her colleagues.

"In short ... she is not safe," the tribunal said.

The tribunal censured Emmerson and cancelled her registration.