Up to one in three mental health patients are being over-prescribed drugs, says the Healthcare Commission.
Medicines for mental health patients must be better managed
A report found mental health patients were more likely to have problems with medicines than those in other trusts.
The healthcare watchdog said management of mental healthcare patients' medicines must improve, and pharmacists should be involved in patient care.
It said the findings were "concerning" given the importance of medicines in mental healthcare.
Healthcare Commission Chief Executive Anna Walker said: "Managing medicines safely, effectively and efficiently is central to the delivery of high quality care that is focused on the patient and gives value for money."
She called on both primary care trusts and mental health trusts to look at their medicines management, and said patients in mental health trusts had told the Commission that they had not been involved as much as they would like in decisions about their medicines.
She said: "This needs to be addressed if trusts expect service users to take their medicines as prescribed."
In research undertaken by the Prescribing Observatory for Mental Health, 36% of people were found to have been prescribed more than the maximum recommended dose of anti-psychotic medicines.
Mental health charity Rethink called for an end to the over-prescription of mental health medicines.
The charity's chief executive Paul Jenkins said: "The Healthcare Commission has once again highlighted a shocking over-prescription of powerful medicines to people in hospital experiencing a mental health crisis.
"As well as defying national guidance, this over-prescription actually delays successful discharge in many cases.
"Everyone has the right to the best evidence-based care, but it is unacceptable that people experiencing a mental health crisis can still be treated as second class citizens."
The Commission said the problem could be detected by an effective clinical pharmacy service.
It found that reviewing medication benefited patients, with 70% of reviews in mental health trusts leading to a change in a person's medicine, and 46% of those reviewed being found not to be taking their medicines appropriately.
David Pruce, Director of Practice and Quality Improvement from the Royal Pharmaceutical Society of Great Britain said: "The evidence shows that medication reviews in mental health by specialist pharmacists can have a major impact, with over 70% of the reviews leading to a change in the patient's medication."
Yet 24% of wards in mental health trusts received no visits from pharmacy staff, compared to only 14% in acute trusts, and just 14% received more than five hours of pharmacy staff time in a week, compared to 64% in acute trusts.
Mr Pruce said: "The future should see specialist mental health pharmacists having an increased role in the care of patients."
National Clinical Director for Mental Health, Professor Louis Appleby said: "We recognise that the safe and effective management of medicines is central to the delivery of high quality patient care.
"This report will help services address a very important issue and ensure that patients are fully involved in decisions about - and get the most from - their medicines.
"We are not complacent and more work is needed to ensure that all Trusts reach the standards of the best."