Not enough articles were available to separate surgery types into those associated with mild, moderate, and severe pain. Also, it was not possible to assess statistically whether IV acetaminophen affected the incidence of opioid side effects, because the end point was either not reported (eg, postoperative nausea and vomiting [PONV] not reported in n = 5 studies and pruritis not reported in n = 13 studies), definitions differed (eg, PONV on visual analog scale, nausea only, vomiting only, or nausea and vomiting combined), or end points occurred infrequently when measured such that the trials were not appropriately powered to assess side effect differences.