A 41-year-old woman has been arrested on suspicion of tampering with controlled drugs at Colchester hospitals.
The woman, from Dunmow, is accused of stealing a morphine based drug while working as agency nurse at Colchester General Hospital.
She was arrested on Wednesday in relation to a number of incidents over the past few months.
An Essex Police spokesman said: “Detectives in Colchester investigating alleged irregularities concering controlled drugs in Essex County Hospital and Colchester General Hospital have arrested a woman on suspicion of theft.
“She has been questioned and released on bail until July 17.”
The nurse, who was working for an agency, was also reported to the Nursing and Midwifery Council, which has imposed an interim order.