The chairman of the Hospital Authority (HA), Henry Fan, said on Thursday that he finds it unacceptable that a public hospital doctor recently prescribed more than 400 days' worth of psychiatric medication to a patient.

Eastern Hospital earlier said that it is undesirable for patients to be given medicine for a long period of time, after a private doctor wrote about the case of the psychiatric patient on social media.

The hospital said the patient, who had been seeing a private doctor, was admitted in April.

Before being discharged, a doctor prescribed him the medication to make sure he would have a sufficient supply should he postpone future appointments, the hospital said.

Speaking to reporters after the HA's board meeting, Fan said the matter will be subject to a review.

"For this case, as you all know, right now the clinical decisions must be made by the doctor on duty. So our review is not necessarily to hold someone accountable or something," he said.

"But rather, we want to give more guidelines to doctors, for them to know what to do."

Fan noted there is also an ongoing review looking at prescribing patients at outpatient clinics with no more than 16 weeks' worth of drugs, saying officials will consider this latest case together with that review.

Last week, the government ordered a comprehensive, systemic review at the HA, following a spate of medical blunders and issues with equipment at public hospitals.

Fan said the authority has shortlisted several people with no links to the authority to form an independent committee for the review.