As with all medications, CELEBREX has side effects which range from moderate to serious. Less serious side effects from CELEBREX may include: upset stomach, diarrhea, bloating, gas, dizziness, nervousness, headache, runny or stuffy nose, sore throat, mild skin rash, back pain, inability to sleep difficulty breathing, swelling of the face, tongue, lips or throat, hives, chest pain, weakness, shortness of breath, slurred speech, problems with vision or balance, black, bloody, or tarry stools, coughing up blood or vomit that looks like coffee grounds, swelling or rapid weight gain, urinating more or less than usual, nausea, upper stomach pain, itching, loss of appetite, dark urine, clay-colored stools, jaundice, skin rash, bruising, severe tingling, numbness, pain, muscle weakness Clinical studies prove that a lower percentage of patients taking CELEBREX reported stomach discomfort (including indigestion, abdominal pain, and nausea) versus those taking prescription ibuprofen and naproxen.