呕吐，俗称反胃、恶心，是由于胃和肠道内容物（食糜）由于受到强力积压经过食道由口腔吐出的动作。

• 呕吐前的反射性反应：呕吐前经常会发生一系列植物性神经兴奋的反应，其中包括：呼吸加深、声门关闭、唾液分泌急剧增加、出汗、呼吸急促和心率加速等。
• 呕吐：在呕吐的过程中腹肌和膈肌急剧收缩，腹腔和胸腔的压强上升，挤压胃中的内容物上升经由口腔吐出。比较剧烈的呕吐会导致十二指肠和空肠上段蠕动加剧，使肠道内容物吐出。

Vomiting, also known as emesis and throwing up, among other terms, is the involuntary, forceful expulsion of the contents of one's stomach through the mouth and sometimes the nose.

Vomiting can be caused by a wide variety of conditions; it may present as a specific response to ailments like gastritis or poisoning, or as a non-specific sequela of disorders ranging from brain tumors and elevated intracranial pressure to overexposure to ionizing radiation. The feeling that one is about to vomit is called nausea, which often precedes, but does not always lead to, vomiting. Antiemetics are sometimes necessary to suppress nausea and vomiting. In severe cases, where dehydration develops, intravenous fluid may be required.