###HUMAN: last time until 20 months ago when did patient 028-23341 get a prescription?, ###ASSISTANT: SELECT medication.drugstarttime FROM medication WHERE medication.patientunitstayid IN (SELECT patient.patientunitstayid FROM patient WHERE patient.patienthealthsystemstayid IN (SELECT patient.patienthealthsystemstayid FROM patient WHERE patient.uniquepid = '028-23341')) AND DATETIME(medication.drugstarttime) <= DATETIME(CURRENT_TIME(), '-20 month') ORDER BY medication.drugstarttime DESC LIMIT 1