Birmingham and Solihull Mental Health NHS Foundation Trust runs services from over 50 sites.
Inspectors criticised the safety of medicines management and said there was a high use of prone - or face-down - restraint.
Bosses at the trust said improvements were being made.
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The inspection by the Care Quality Commission (CQC) rated the trust as "requires improvement" overall. It was previously rated as "good", in 2014.
Inspectors said:
However, inspectors highlighted several areas of good practice and said staff were caring, compassionate and kind and treated patents with dignity and respect.
The CQC added staffing levels were generally safe and sufficient to provide good care.
The trust said it has already made improvements, including appointing a medication safety officer.
Chief executive John Short, said: "We recognise that the CQC has identified some areas where we did not meet the high standards we set ourselves.
"Since the inspection, work has already been completed in a number of key areas and is under way to address the other concerns raised."
The inspection took place between 27 and 31 March.

Falcons twice led through Vereniki Goneva and Rob Vickers tries, with James Short and Harry Williams replying to level before a Simmonds penalty put Chiefs 17-14 up at the break.
Simmonds landed his fourth kick to convert a second-half penalty try.
A Sam Skinner score and a second Short effort ensured the bonus-point victory.
The win lifts them to within a point of leaders Wasps, who face Gloucester on Sunday.
For 20-year-old fly-half Simmonds, it was the perfect day with the boot as he replaced injured veteran Gareth Steenson in a side that was missing a number of players - including England's Jack Nowell and Henry Slade - due to Six Nations duties.
Newcastle, who a week earlier earned an impressive 46-31 win over Northampton at Kingston Park, made a strong start with Goneva crossing for a superb try, which started with a bustling run from Calum Green.
Short, who would finish the day by touching down for the fifth time in two games, restored parity for the first time with a 90-metre effort, which came from an error as Newcastle closed in on a second try.
While Exeter were made to work hard for their first-half lead after Vickers again edged Falcons ahead, the hosts were more ruthless after the break and heavily restricted Newcastle, who are still without a win at Sandy Park.
Exeter Chiefs assistant coach Ali Hepher:
"Newcastle are a good side and in good form and came here with a good deal of confidence but we started poorly, especially in defence.
"We were hesitant in that first half particularly when we had ball in hand as we needed to run hard instead of trying the clever ball.
"There was plenty to address at half-time but our defence was outstanding in that second half and to earn a bonus point was invaluable.
"Moving one point into second and above Saracens at this stage is not important as the top four places are really tight but we are hoping to remain there and to secure a top two finish would be really nice."
Newcastle Falcons director of rugby Dean Richards:
"I'm disappointed as we started really well but we weren't accurate enough and this allowed them back into the game.
"We should have been further in front but we didn't take our chances and too many kicks went straight into touch.
"They are very good side, who are incredibly patient, as they wait for a chink in your defence before striking."
Exeter: Dollman; Woodburn, Whitten, Devoto, Short; Simmonds, Maunder; Moon, Yeandle (capt), Williams, Lees, Parling, Horstmann, Armand, Waldrom.
Replacements: Malton, Rimmer, Low, Skinner, Atkins, Townsend, Hooley, Hill.
Newcastle: Tait; Goneva, C Harris, Waldouck, Sinoti; Hodgson, Takulua; Vickers, Cooper, Wilson, Green, Olmstead, M Wilson, Welch (capt), Latu.
Replacements: Sowrey, B Harris, D Wilson, Young, Chick, Egerton, Delany, Burdon.
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A mental health trust that provides services for 1.2m people in the West Midlands has been told by a health watchdog it "requires improvement".
[NEXT_CONCEPT]
Joe Simmonds kicked 11 points in his first Premiership start to help Exeter Chiefs move into second in the table with victory over Newcastle Falcons.