instruction: when patient 002-20631 was prescribed furosemide (lasix) tab 40 mg first time a month before.
response: 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 = '002-20631')) AND medication.drugname = 'furosemide (lasix) tab 40 mg' AND DATETIME(medication.drugstarttime, 'start of month') = DATETIME(CURRENT_TIME(), 'start of month', '-1 month') ORDER BY medication.drugstarttime LIMIT 1