Patients and staff were partially evacuated from Chapel Allerton Hospital at around 3pm yesterday.
A West Yorkshire Police spokesperson today said: "A man has been arrested following a suspect package incident at Chapel Allerton Hospital in Leeds yesterday.
"The 19-year-old, from Bradford, was arrested last night on suspicion of drugs offences and remains in custody.
"Police were contacted at 2.57pm yesterday about a suspect package in a toilet at the hospital. A cordon was put in place and the hospital carried out a partial evacuation while the package was examined and declared safe at 5.20pm."