Inclusion Criteria:  American Society of Anesthesiologists I or II. Sex: Both sexes. Age between 18 and 50. Height 155-180 cm. Patients scheduled for arthroscopic anterior cruciate ligament (ACL) repair under spinal anesthesia.  Exclusion Criteria:  Declining to give written informed consent. History of allergy to the medications used in the study. Had a history of drug or alcohol abuse. Taking opioids or sedative medications. Inability to communicate with patients to evaluate the postoperative pain. Need for postoperative ICU hospitalization. Hepatic or renal failure. Patients with a history of taking duloxetine or any SSRIs. Contraindications to regional anesthesia (including coagulopathy and local infection). Psychiatric disorders with antipsycotics or antidepressants (tricylic or MAOIs). Antiplatelets (aspirin, clopidogrel) or anticoagulant (warfarin). Quinolones (ciprofloxacin).