Acute wards for adults of working age and psychiatric intensive care units at the trust were rerated inadequate for safe and downgraded from requires improvement to inadequate following an inspection in October and November.
The overall rating for the trust remained requires improvement and the trust was issued with warning notices to ‘focus attention on making rapid, specific changes to improve people's safety'.
Amanda Lyndon, CQC deputy director of operations in the Midlands, said: ‘During our inspection of this service, we found a deterioration in how well it was being led.'
Lyndon said leaders were not ensuring the service was staff appropriately with people's escorted leave being cancelled due to ineffective staff management.
The deputy director added leaders ‘also relied too heavily on bank staff who didn't know people using the service, or their needs very well, which made them uncomfortable'.
The CQC said managers had provided assurance that recruitment was under way to increase staffing levels, particularly on night shifts.
A spokesperson for Birmingham and Solihull Mental Health NHS Foundation Trust said: ‘We acknowledge and accept the Care Quality Commission's findings following their inspection of our Zinnia Centre.
‘Since the inspection we have taken rigorous steps to strengthen leadership, address staffing shortages and provide intensive training to ensure staff are able to deliver the highest quality of care to our patients and service users.
‘We still have work to do and are always committed to providing the best possible care for all our service users.'