Western Australia's Mental Health Minister has apologised to a man who was arrested and drugged after being mistaken for a patient from a psychiatric hospital.

Police arrested the man on December 16 as he fitted the description of a patient who had gone missing from Graylands Hospital in Perth.

Graylands staff wrongly confirmed the man's identity before administering a strong antipsychotic drug for schizophrenia.

They realised their mistake when the man had an adverse reaction to the drug and was rushed to hospital.

Greens MP Alison Xamon has called for an inquiry.

"I'm absolutely horrified to have heard about this," she said.

"I think it raises so many questions about what's happening with the procedures.

"It certainly requires some very serious investigation, if not inquiry."

Mental Health Minister Helen Morton says she is sorry for the distress the man suffered and there is no excuse for such a terrible mistake.

She says those responsible will be held accountable once a review is completed.