To provide an opioid analgesic formulation sustaining the activities for a long period, and enabling once dose per day.

The sustained release oral solid dosage form of the opioid analgesics is provided as a multiparticulate system which is bioavailable and which provides an effective blood level of the opioid analgesic for at least about 24 hours. A unit dose of the opioid analgesic contains a plurality of substrates including the opioid analgesic in sustained release form. The substrates have a diameter from about 0.1 mm to about 3 mm.