The Centers for Disease Control and Prevention's 2016 Guideline for Prescribing Opioids for Chronic Pain aimed to reduce unsafe opioid prescribing. It is unknown whether the guideline influenced prescribing in the target population: patients with chronic, noncancer pain, who may be at particular risk for opioid-related harms. To study this question, we used 2014-18 data from a commercial claims database to examine associations between the release of the guideline and opioid dispensing in a national cohort of more than 450,000 patients with four common chronic pain diagnoses. We also examined whether any reductions associated with the guideline were larger for diagnoses for which there existed stronger expert consensus against opioid prescribing. Overall, the guideline was associated with substantial reductions in dispensing opioids, including a reduction in patients' rate of receiving at least one opioid prescription by approximately 20 percentage points by December 2018 compared with the counterfactual, no-guideline scenario. However, the reductions in dispensing did not vary by the strength of expert consensus against opioid prescribing. These findings suggest that although voluntary guidelines can drive changes in prescribing, questions remain about how clinicians are tailoring opioid reductions to best benefit patients.