Gastroenteritis: This is often the most common cause of nausea and vomiting, typically resulting from a viral or bacterial infection. It's characterized by inflammation of the stomach and intestines, leading to symptoms like diarrhea, abdominal cramps, and fever, in addition to nausea and vomiting.

Food Poisoning: Similar to gastroenteritis, food poisoning can cause nausea and vomiting, usually after consuming contaminated or spoiled food. Symptoms can vary depending on the causative agent but often include abdominal cramps and diarrhea.
Pregnancy: Morning sickness is a common symptom experienced by many pregnant women, typically during the first trimester. It can range from mild nausea to severe vomiting.
Medication Side Effects: Many medications can cause nausea and vomiting as side effects. This is particularly common with chemotherapy, antibiotics, and pain medications.
Motion Sickness: This condition occurs in response to certain motions, such as during travel by car, boat, plane, or other vehicle. It's caused by conflicting signals sent to the brain by the senses of sight, hearing, and balance.

Appendicitis: Although less common, appendicitis can present with nausea and vomiting, especially if the appendix ruptures. It's crucial to consider this diagnosis to avoid missing a potentially life-threatening condition.
Intestinal Obstruction: This is a blockage that prevents the normal flow of the products of digestion, including food, fluid, and gas. Symptoms include severe abdominal pain, nausea, vomiting, and constipation.
Pancreatitis: Inflammation of the pancreas can cause severe abdominal pain, nausea, and vomiting. It requires immediate medical attention due to potential complications.
Kidney Stones: While primarily known for causing severe pain, kidney stones can also lead to nausea and vomiting, especially if they cause an obstruction.

Brain Tumors: In rare cases, brain tumors can cause nausea and vomiting, particularly if they increase intracranial pressure or affect areas of the brain involved in balance and equilibrium.
Meningitis: This infection of the membranes surrounding the brain and spinal cord can cause nausea and vomiting, along with symptoms like headache, fever, and stiff neck.
Gastroparesis: A condition where the stomach takes too long to empty its contents, often causing nausea, vomiting, and feeling full after eating only a small amount of food.
Cyclic Vomiting Syndrome: A disorder characterized by recurring episodes of severe nausea and vomiting, with no apparent cause, and periods of normal health in between episodes.