What Causes Nausea and Vomiting? A Clinical Overview

Nausea and vomiting are among the most common symptoms in medicine — virtually everyone experiences them at some point in their lives. But ‘feeling sick’ is not a diagnosis in itself: it is a signal from your body that something has disrupted the finely tuned systems that control your gut, brain, and balance. Understanding what is causing your nausea is the first step to choosing the right treatment.

What follows covers the full range of causes, how the vomiting reflex actually works, the symptoms that should prompt urgent care, and every treatment option — OTC and prescription — available in the UK.

For a complete clinical overview of all available UK treatment options, see our nausea and vomiting guide →.

How the Vomiting Reflex Works

To understand what causes nausea, it helps to know how the body triggers it. The vomiting reflex is controlled by two key brain structures working in concert.

Additional signals arrive from the vestibular system (inner ear balance organs), the gut via the vagus nerve, and higher brain centres processing emotions such as anxiety, fear, and pain. Different antiemetic drugs work by blocking signals at different points in this pathway — which is precisely why choosing the right medication depends on understanding the cause of your nausea.

Common Causes of Nausea and Vomiting in the UK

1. Gastroenteritis (Stomach Bug)

Gastroenteritis is the most common cause of acute nausea and vomiting in the UK, typically caused by viral infections such as norovirus or rotavirus. The infection irritates the gut lining and stimulates the vagus nerve, triggering the vomiting reflex. Symptoms typically resolve within 24–72 hours. Treatment centres on oral rehydration — small frequent sips of water or electrolyte drinks — and a bland diet. Anti-sickness medication can help manage symptoms during the acute phase.

2. Food Poisoning

Food poisoning occurs when contaminated food introduces bacteria (Salmonella, Campylobacter, Staphylococcus aureus, E. coli), viruses, or toxins into the digestive system. Onset varies from 30 minutes (with pre-formed toxins) to several days (with Salmonella). Most cases resolve within 24–48 hours with rehydration. Antibiotics are only required for specific organisms on clinical advice.

3. Migraine

Nausea affects approximately 80% of migraine sufferers and arises through direct stimulation of the CTZ and vomiting centre during an attack. Critically, migraine also slows gastric emptying — meaning oral pain relief may sit unabsorbed in the stomach at the time it is most needed. Domperidone’s prokinetic action restores gastric motility, improving analgesic absorption and making it particularly useful in this context.

4. Vertigo and Inner Ear Disorders

Vertigo — the sensation that you or the world around you is spinning — is a potent trigger for nausea. When the vestibular system sends abnormal signals (as in BPPV, vestibular neuritis, labyrinthitis, or Menière’s disease), the brain interprets the conflict between visual and vestibular inputs as a sign of poisoning and triggers nausea. Cyclizine (an H1 antihistamine and anticholinergic) is first-line for vestibular nausea; prochlorperazine is an alternative. See our guide to how cyclizine helps with vertigo-related nausea.

5. Pregnancy (Morning Sickness and Hyperemesis Gravidarum)

Nausea and vomiting in pregnancy affects up to 80% of pregnant women, typically beginning around week 6, peaking at weeks 8–12, and resolving for most women by week 14–16. Despite its name, morning sickness can occur at any time of day. It is strongly associated with rising levels of human chorionic gonadotrophin (hCG). Hyperemesis gravidarum — severe vomiting affecting 1–3% of pregnancies — causes weight loss and dehydration requiring clinical intervention. Safe first-line antiemetics in pregnancy include cyclizine, promethazine, and prochlorperazine per RCOG Green-top Guideline No.69. See our guide to nausea in pregnancy: morning sickness and hyperemesis treatment.

6. Motion Sickness (Travel Sickness)

Motion sickness occurs when there is a conflict between movement detected by the inner ear and what the eyes see. The brain interprets this sensory mismatch as a sign of disorientation, triggering the vomiting reflex. It is extremely common during car, boat, plane, and train travel. OTC options include cyclizine 50mg (take 1–2 hours before travel), hyoscine, cinnarizine, and promethazine. See our guide to motion sickness tablets: cyclizine, hyoscine, and travel sickness treatment UK.

7. Anxiety and Psychological Causes

The gut and brain are directly connected via the enteric nervous system and the vagus nerve — sometimes called the gut–brain axis. Anxiety activates the fight-or-flight response, releasing adrenaline and cortisol which slow gastric emptying and cause stomach muscle contractions, producing nausea. Anxiety-related nausea is typically situational, associated with specific triggers, and rarely leads to actual vomiting. Persistent anxiety-related nausea may benefit from psychological support alongside short-term antiemetics.

8. Medication Side Effects

Many commonly prescribed and over-the-counter medicines cause nausea as a side effect, through various mechanisms.

Domperidone is particularly useful for opioid-induced nausea, as it blocks D2 receptors in the CTZ without crossing the blood–brain barrier, avoiding the neurological side effects associated with metoclopramide. See our guide to domperidone tablets for nausea and digestive relief.

9. Gastroparesis and Functional Digestive Disorders

Gastroparesis is a condition in which the stomach empties more slowly than normal despite the absence of a physical blockage. This leads to prolonged nausea, early satiety, bloating, and upper abdominal discomfort, typically worsening after eating. It is most commonly associated with diabetes, previous gastric surgery, or neurological conditions. Domperidone’s prokinetic action makes it the preferred agent, particularly in Parkinson’s disease where it does not worsen motor symptoms.

10. Other Clinically Important Causes

• Appendicitis — nausea often precedes right iliac fossa pain; requires urgent assessment
• Bowel obstruction — projectile vomiting, abdominal distension, constipation
• Renal colic — severe flank pain with accompanying nausea and vomiting
• Diabetic ketoacidosis (DKA) — nausea, vomiting, fruity breath, altered consciousness in Type 1 diabetes
• Raised intracranial pressure — early-morning nausea with headache; may indicate a serious neurological condition
• Liver and gallbladder disease — cholecystitis, hepatitis, and biliary colic all present with nausea
• Alcohol excess — direct GI irritation and CTZ stimulation

Red Flag Symptoms: When to Seek Urgent Help

See a doctor promptly (same day or next available appointment) if:

• Vomiting persists for more than 48 hours without improvement
• You cannot keep down any fluid for more than 24 hours
• You are showing signs of dehydration: dark urine, dizziness, dry mouth, no urination for 8 or more hours
• You are pregnant and cannot tolerate any food or fluid (possible hyperemesis gravidarum)
• You have unexplained weight loss alongside persistent nausea
• Nausea is a new symptom in a patient with known cancer or who is on chemotherapy
• You have recently started a new medication and believe it may be causing the nausea

How Long Does Nausea Last? A Timeline by Cause

Anti-Sickness Treatment Options in the UK

Once you understand the cause, choosing the right treatment becomes straightforward. The main options are:

• Self-care and home remedies — rehydration, ginger, acupressure, small frequent meals — appropriate for mild nausea from gastroenteritis or anxiety
• Over-the-counter antiemetics — cyclizine, hyoscine, cinnarizine — available at UK pharmacies without prescription
• Prescription antiemetics — domperidone, cyclizine (prescription-strength), prochlorperazine, ondansetron — depending on cause and severity