IRCT2017012922697N2 IRCT 2017-05-01 Vice chancellor for research Mashhad university of medical sciences the evaluation of Clonidine versus Ondansetron for control of pain, nausea & vomiting after Orthognathic surgery. Clonidine versus Ondansetron in Orthognathic surgery. The evaluation of pre-operative Clonidine versus Ondansetron prescription for control of pain, nausea & vomiting after Orthognathic surgery. 2017-04-04 anticipated 40 Complete https://irct.ir/trial/19523 interventional Randomization: Randomized, Blinding: Not blinded, Placebo: Not used, Assignment: Parallel, Purpose: Treatment, Other design features: As the effectiveness of clonidine or ondansetron in comparison with placebo for pain and PONV in surgical field is proved in other clinical trial studies; we decided to not have placebo in this study. ّFurthermore, the surgeon and anesthesiologist were aware of the drug types in order to prevent the peri and post operative complications; but the student who will record data and analyzing committee of information was blind. the patients were aware of the study interventions because of consent letter. Simple randomization ( Random number table) will be used in this study. 3 Condition 1: pain after orthosurgery. Condition 2: nausea and vomiting after orthosurgery. Condition 3: Jaw deformity. Intervention 1: Intervention 1:Prescription of ondansetron (8 mg) (150 µg) in form of oral tablets that have been dissolved in 20 ml of water (as intervention) one hour before general anesthesia of orthosurgery. Intervention 2: Intervention 2:Prescription of clonidine (150 µg) in form of oral tablets that have been dissolved in 20 ml of water (as intervention) one hour before general anesthesia of orthosurgery.