The spray was used to "protect police officers and others nearby from violent behaviour" when methods of "peaceful persuasion" had failed, said an ACPO spokesman.
His comments follow revelations in the Independent on Sunday yesterday of a report by Maudsley Psychiatric Hospital in London that CS spray was being used "inappropriately".
Staff were being impeded from treating patients sprayed with the substance because they were also being affected, said a hospital spokesman.
"There are cases where CS spray is being used inappropriately in non- violent situations.
"It is used to restrain and subdue patients before bringing them into hospitals."
But the ACPO said the report, a nationwide survey of mental health trusts, gave no data to back up the claims and was "mainly anecdotal comment".
The use of CS spray was carefully regulated. The spray was used only in self-defence by police officers who had been trained in its use.
"The suggestion that CS spray should not be used against mental health patients is absurd and extremely dangerous, not just to police officers but to staff and other patients," he said.
One of the report's authors, Fraser Bell, a senior research nurse at the Maudsley Psychiatric Hospital, called for an end to the use of CS spray against mental health patients.
He worked on the survey with the hospital's director of clinical services, Ben Thomas, and believes nurses and police should meet and discuss the reduction of its use.
"There is a minority of cases where it is being used as a first line of defence instead of a last line of defence," he said.
"There are concerns about its possible lasting effects on mental health patients. We want to see some scientific research into this. What did the police do before they had CS spray? They used their powers of persuasion."
He also warned that nursing staff were suffering because they were getting particles of the chemical on their clothes and skin after trying to treat patients affected by CS spray.Reuse content