A Perth doctor has been banned from practising medicine after admitting to professional misconduct which included sexualised behaviour towards a patient, to whom he also over-prescribed potent medication.

In a judgement published this week, the State Administrative Tribunal found the conduct of Gregory Duck amounted to "serious breaches" of the medical code for doctors, including "incompetence, poor medical practice and sexualised behaviour".

The tribunal was told Gregory Duck started seeing the woman in December 2012 when he obtained her history with methadone use.

He then formed an inappropriate relationship with her that included taking her out to dinner, buying her gifts such as lingerie, which he photographed her in, and having consultations with her at his home.

On one occasion the woman went to a hotel room where he was staying and after she took heroin and collapsed, Dr Duck did not call an ambulance, and instead stayed with her, alone in the room.

The tribunal was told that on about 50 occasions over an 18-month period, Dr Duck prescribed the woman varying amounts of medications including Xanax and Valium.

In some instances he wrote the prescriptions in the woman's absence, and after paying for and collecting the drugs, kept them in a locked drawer in office to give to her.

He also planned for the woman to undertake a detoxification programme in hotel room but she did not end up participating.

In a written submission to the tribunal, Dr Duck maintained "there was never any guilty mind or bad intent" on his part, and he became "determined not to reject (the woman) as others done".

He also submitted "there was no injury to the patient, physical or psychiatric".

Dr Duck 'used iPhone torch for pap smear'

In its ruling, the tribunal described Dr Duck's conduct as "serious" saying "it demonstrated a very serious lack of awareness of, and acting in accordance with professional boundaries" which it said appeared in this case to have "almost completely collapsed".

"It is apparent that Dr Duck had allowed (the patient) to manipulate him, rather than to treat (the patient) in accordance with his obligations as a doctor."

The tribunal also said the over-prescription of drugs to a patient put them at risk of "over medication" and "of engaging in illicit activities".

It took into account what it called Dr Duck's "extensive and serious disciplinary history" for previous breaches of the Medical Board's Code of Conduct and Guidelines, which included drug dependency and using a torch on his iPhone to conduct a pap smear.

Dr Duck, who is now 62, has not practised since he was suspended in May 2014, and the tribunal ruled he should not be allowed to re-apply for registration for another two years.