According to Drugs.com, the biological half-life of intravenous morphine in healthy volunteers is around 1.5 to 2 hours. Traces of morphine are detectable in urine for up to 48 hours after the dose.
Within 24 hours, the body excretes around 90 percent of a morphine dose in urine, Drugs.com states. Approximately 7 to 10 percent of the drug is later expelled in the feces. Intrathecal or epidural administration of morphine produces pain relief that is capable of lasting for up to 24 hours. Intrathecal and epidural administration of morphine generally includes lower doses due to the longer duration of action.