What is the main symptom of gastroesophageal reflux disease (GERD)?

The main symptom of gastroesophageal reflux disease (GERD) is heartburn. This condition occurs when stomach acid flows back into the esophagus, leading to a burning sensation in the chest or throat. Heartburn is often described as a feeling of warmth or discomfort that can be exacerbated by specific activities, such as lying down or eating certain foods. It is directly related to the reflux of stomach contents into the esophagus, which is a hallmark of GERD.

While nausea, stomach pain, and diarrhea can occur in various gastrointestinal conditions, they are not the primary or most distinctive symptoms of GERD. Nausea and stomach pain are often associated with different digestive issues, while diarrhea typically pertains to conditions affecting the intestines or digestive process rather than specifically indicating reflux. Thus, heartburn stands out as the defining symptom of GERD, making it the correct answer.