Melissa Swift, 25, spiked water jugs and drinks bottles at Goldfield Court care home, West Bromwich, in July 2014.
Seven members of staff and 23 residents were taken ill.
Care worker Swift admitted three counts of attempted murder. She was ordered to serve at least eight years before she is eligible for parole.
She will be treated in a secure mental institution until she is well enough to be taken to prison.
The ex-special constable, formerly of Hambletts Road, West Bromwich, also admitted threatening to kill another colleague as well as her stepsister.
Birmingham Crown Court heard Swift, who has depression and an undiagnosed personality disorder, represents a significant risk of causing serious harm to the public.
Commenting on the case, Det Ch Insp Michaela Kerr, from West Midlands Police's Public Protection Unit, said: "Melissa deceived her colleagues and hatched a plan to cause ill to those she worked with as a result of some malice, for which we have never truly discovered the cause.
"Thankfully no one was seriously injured as a result of what she did, but the story could so easily have been different."
In a statement, Housing & Care 21, which runs the home, said it welcomed the conclusion of this case.
A spokesperson said: "We thank the staff at Goldfield Court for the way they conducted themselves during the incident and subsequent investigation, and for the way they have continued to provide excellent support and care to our residents throughout.
"We are also grateful to residents for their continued co-operation and understanding."
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