A 25-year-old woman is evaluated for an 8-month history of epigastric abdominal pain. The pain is episodic, but it is present more often than not. There do not seem to be any factors that clearly exacerbate or alleviate the pain. She notes occasional nausea and poor appetite but has not had weight loss. Her medical history is notable for gastroesophageal reflux disease. There is no family history of gastrointestinal malignancy. Her only medication is omeprazole, 20 mg/d.

On physical examination, vital signs are normal. Abdominal examination reveals generalized abdominal tenderness to light palpation but is otherwise normal.

Testing for Helicobacter pylori is negative. Owing to ongoing symptoms despite antisecretory therapy, upper endoscopy with gastric and small-bowel biopsies is performed; results are normal.

Which of the following is the most appropriate treatment?