Consenting patients will be randomized to receive either a single dose of caffeine, 500 mg, or saline placebo, administered as a single IV dose approximately 15 minutes before emergence from anesthesia. All patients will receive our customary anti-emetic prophylaxis, determined by four major risk factors for PONV: female gender, nonsmoking status, history of PONV or motion sickness, and perioperative opioid use. Patients at low risk for PONV (no risk factors) will receive no prophylaxis; patients at moderate risk for PONV (1 or 2 risk factors) will receive dexamethasone 8 mg at induction plus dolasetron 12.5 mg approximately 15 min before the end of anesthesia; patients at high risk for PONV (3 or 4 risk factors) will receive the same treatment as those at moderate risk, plus additional prophylaxis at the discretion of the attending anesthesiologist (e.g., scopolamine patch, metoclopramide 10 mg IV, or other standard drugs).