A man who was wrongly administered a strong antipsychotic drug at a Perth mental hospital after being mistaken for a missing patient is probably entitled to compensation, the state's mental health minister says.
Police arrested the man on December 16 because he fitted the description of a patient who was missing from Graylands Hospital.
Staff wrongly confirmed the man's identity and gave him a antipsychotic drug for schizophrenia.
The mistake was realised when the man had an adverse reaction to the medication and had to be rushed to hospital.
Mental Health Minister Helen Morton told AAP on Thursday the man was probably entitled to compensation over the mix-up.
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"On the face of it, this is clearly a case where compensation should be made," she said.
"However, we will have to await the outcome of the full inquiry and we are aware of all the facts before the matter can be fully considered."
Ms Morton said the case was an "absolute priority" for her and she had asked for an inquiry to take place in a week.
"I am hoping this is an isolated incident made by human error but I will know more about that from the inquiry," she said.
The minister said she was "shocked and appalled" that such an error could occur.
"I am very sorry for the distress and hurt that the misidentified man has endured," Ms Morton said.
"I find it hard to imagine that if proper processes were followed there is any excuse for such a terrible mistake to be made.
"I will await the outcome of the clinical review; however, people must be held accountable for this dreadful mistake and to ensure that it never happens again."
Ms Morton said she was also seeking clarification from the Health Department about the man's follow-up care.
