Dr. Bjordal suggests that we graded evidence for acetaminophen too positively. In his letter, Dr. Bjordal describes one trial as evaluating acute low back pain when it actually evaluated chronic low back pain (9). Otherwise, our descriptions of the evidence are similar (Appendix Tables 10 and 11 (2)). We agree that our evidence ratings for acetaminophen were generous given some inconsistency among trials of acute low back pain, and lack of direct evidence and small benefits for chronic low back pain. We re-rated evidence for acetaminophen for acute low back pain fair quality with moderate benefits, and for chronic low back pain fair quality with small benefits (see Correction). Because of acetaminophen's favorable safety profile compared to other pharmacologic therapies, these changes do not change our recommendation to consider it as a first-line option for pharmacologic therapy (1).