Western Australian's Mental Health Minister Helen Morton has revealed more details about a man who was mistaken for a mental hospital patient and given antipsychotic drugs.

The 22-year-old man was mistaken for an involuntary patient who had left Graylands Hospital in Perth without permission earlier this month.

Both men are Aboriginal. The wrong man was given an antipsychotic drug and suffered a bad reaction before the mistake was discovered.

He was rushed to hospital after his reaction.

Ms Morton says the identity mix-up happened partly because the man answered to the name of the patient the authorities were looking for.

She says the man who was wrongly detained was known to the health system and to police, although probably not to the officers who picked him up.

Ms Morton says he responded to the missing patient's name and told police he wanted to "go back" to Graylands.

She says after he was taken to Graylands, the duty doctor said he needed his Clozapine.

"He was administered that medication in tablet form and it was in the process of being taken to his room that it became known to staff that he wasn't the involuntary patient," she said.

"He had an adverse reaction and within two hours of being back at Graylands he was admitted to Sir Charles Gardiner Hospital."

The minister says staff came to believe they had the wrong man when he did not know where his room was.

"There are some amazingly stringent processes and procedures that are required, both when a person is being admitted and when a person is being administered schedule four drugs," Ms Morton said.

"Those policies and procedures are currently being reviewed in light of this and also whether those policies and procedures were followed correctly by the people concerned."

Authorities in WA have belatedly made contact with the man who was wrongly detained and drugged.

He is reportedly in good health, but criticism over the incident continues to mount. Aboriginal people have expressed shock and anger over the case.

Noongar elder Ben Taylor says the incident must never happen again.

"A black man walked out of there and they were looking for him, what did they do? The police, they just picked up the first black man they saw, even though he was homeless. I was shocked. This is winding back the clock," he said.

Elder Wanjuri says the incident has raised many questions.

"What does this say about the police and the staff at the hospital? Why weren't the Aboriginal mental health people contacted? Because surely they would've been able to communicate," he said.

"It's just a very sad thing and it must never happen again. But it may do, I mean this may have happened in the past, who knows?"