Sustained release oral solid dosage forms of opioid analgesics are provided as multiparticulate systems which are bioavailable and which provide effective blood levels 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.