The MQOR 40 is a validated instrument that was specifically design to evaluate patient recovery after anesthesia and surgery. This instrument can be particularly valid to examine interventions which affect different spheres of patient recovery as is the case of diphenhydramine. The objective of this study is to determine a dose response effect of preoperative diphenhydramine on postoperative quality of recovery after ambulatory surgery. The use of preoperative diphenhydramine can improve patient's quality of recovery, decrease postoperative pain, opioid consumption and opioid related side effects after ambulatory surgery.