OGD is a medical examination procedure. During the procedure, the doctor uses a thin and flexible instrument called an endoscope to examine the inside of the upper digestive tract, including the oesophagus, the stomach and the duodenum. The endoscope has an optical lens, a light source and a camera at the tip, which allows the doctor to see these areas when the instrument travels its way down. A biopsy of a suspected lesion or an area of concern may be taken for further pathological diagnosis if necessary. The procedure is usually done under intravenous sedation or monitored anaesthetic care (MAC) administered by an anaesthetist. OGD is generally safe, but patients may still develop minor discomforts including nausea and feeling of tummy upset and distention. This procedure has to be performed in special day surgery centres or hospitals, depending on individual patients’ risks and needs.