A man with first hand experience of Waikato mental health services, says he's shocked over the latest incident involving an 11-year-old

The girl - believed to have non-verbal autism - was mistaken for a missing 20-year-old patient, and wrongfully administered anti-psychotics at the Henry Bennett Centre earlier this month.

Former Waikato DHB member, and outspoken centre critic Dave Macpherson says this tops all the horror stories he's heard, because she wasn't even a patient but a member of the public.

MacPherson's son took his life while under the centre's care in 2015.

Health New Zealand and Police are both conducting reviews into the latest incident.