Codeine/acetaminophen and hydrocodone/acetaminophen combination tablets for the management of chronic cancer pain in adults: a 23-day, prospective, double-blind, randomized, parallel-group study.

Background: Analgesics are an essential component of the treatment of cancer-associated pain. Pharmacologic treatment is usually begun with nonopioid analgesics, most frequently acetaminophen. If pain relief is not achieved, the so-called "weak" opioids, such as codeine and hydrocodone, may be used in combination with acetaminophen.