The purpose of this study is to determine whether celecoxib is effective in the treatment postoperative pain after thyroidectomy.

The research hypothesis:

There is a difference in postoperative morphine consumption in the first 24 hours after thyroidectomy between patients who received celecoxib or placebo.

Postoperative pain has been concerned in the past few years by both the anesthesiologists ans the surgeons. COX2-inhibitors have played an important roles in postoperative pain with minimal side effects.

Comparison(s): There is a difference in postoperative morphine consumption in the first 24 hours after thyroidectomy between patients who received celecoxib and placebo.

Inclusion Criteria:

1. Patient ASA physical status I-III.
2. Scheduled for an elective thyroidectomy.
3. Body weight > or = 40kg
4. Can operate a patient-controlled analgesia (PCA) device.

Exclusion Criteria:

1. History of asthma, acute rhinitis, nasal polyps, angioneurotic edema or urticaria following the administration of aspirin or other NSAIDs.
2. Known hypersensitivity to morphine or sulfonamides.
3. History of hepatic dysfunction.
4. Creatinine clearance < 30ml/min.
5. History of bleeding tendency.
6. History of gastrointestinal bleeding or active peptic ulcer.
7. Known case of inflammatory bowel disease.
8. Patient with severe heart failure.