What are the possible causes of nausea?

Causes of Nausea

Nausea has an extensive differential diagnosis spanning gastrointestinal, central nervous system, endocrine/metabolic, medication-related, and psychiatric etiologies that must be systematically evaluated through targeted history and examination. 1

Primary Etiologic Categories

Gastrointestinal Causes

The most common GI causes include:

• Gastroparesis (delayed gastric emptying) - occurs in 20-40% of diabetic patients and 25-40% of those with functional dyspepsia, presenting with nausea, vomiting, and postprandial fullness 1
• Functional dyspepsia - affects approximately 20% of the US population with overlapping symptoms of nausea, early satiety, and postprandial bloating 1
• Bowel obstruction - particularly malignant obstruction in advanced colorectal and ovarian cancer 2
• Constipation - a frequently overlooked but common cause, especially in patients on opioids or anticholinergic medications 2, 3
• Gastric outlet obstruction 2
• Gastrointestinal infections - typically self-limited, causing acute nausea/vomiting lasting <48 hours 4, 5

Medication-Induced Causes

• Opioids - cause nausea in up to 50% of patients when initiated or dose-escalated 6, 3
• Chemotherapy - affects 70-80% of cancer patients, with risk varying by specific agent, dose, schedule, and route 2
• Anticholinergic medications - contribute to dysmotility 2

Central Nervous System Causes

• Increased intracranial pressure - from brain metastases, intracranial hemorrhage, or mass lesions 2, 5
• Meningitis - requires urgent evaluation when accompanied by fever and neurologic signs 7
• Migraine headaches - strongly associated with cyclic vomiting syndrome 8
• Vestibular disorders - motion sickness and labyrinthine dysfunction 9

Endocrine/Metabolic Causes

• Pregnancy - must be considered in any woman of childbearing age 5
• Hypercalcemia - common in advanced malignancy 2, 3
• Diabetic gastroparesis - represents vagal neuropathy; hyperglycemia itself causes antral hypomotility 1
• Addison's disease and hypothyroidism - can mimic other causes 8
• Hepatic porphyria 8

Specific Syndromes

• Cyclic vomiting syndrome (CVS) - stereotypical episodes of acute-onset vomiting lasting <7 days, separated by symptom-free intervals, often triggered by stress (70-80% of cases), sleep deprivation, or hormonal fluctuations 8
• Cannabinoid hyperemesis syndrome (CHS) - requires prolonged (>1 year) heavy cannabis use (≥4 times weekly) preceding symptom onset, with resolution after 6 months of cessation 8

Critical Diagnostic Approach

History Elements to Elicit

Differentiate vomiting from regurgitation, rumination, and bulimia. Document:

• Duration, frequency, severity, and temporal pattern of symptoms
• Relationship to meals (postprandial symptoms suggest gastroparesis or functional dyspepsia) 1, 10
• Triggers: stress, menstrual cycle, travel, infections, fasting, exercise 8
• Associated symptoms: abdominal pain, headache, neurologic changes, fever
• Medication history including opioids, chemotherapy, and over-the-counter agents
• Cannabis use patterns (frequency, duration, timing relative to symptom onset) 8
• Hot water bathing behavior (present in 48% of CVS patients without cannabis use, not pathognomonic for CHS) 8

Physical Examination Priorities

• Signs of dehydration and metabolic derangement
• Neurologic examination for focal deficits or signs of increased intracranial pressure
• Abdominal examination for obstruction, organomegaly, or peritoneal signs
• Assessment for complications of vomiting (aspiration, Mallory-Weiss tears)

Initial Laboratory Evaluation

When acute nausea lacks obvious infectious or iatrogenic cause:

• Urine pregnancy test (all women of childbearing age)
• Complete blood count
• Comprehensive metabolic panel (electrolytes, glucose, calcium, liver function)
• Amylase and lipase
• Thyroid-stimulating hormone
• Urinalysis
• Stool studies with cultures if diarrhea present 4, 5

Imaging Considerations

• Abdominal radiography - first-line for suspected obstruction
• Abdominal CT - for unclear etiology with concerning features
• Head CT - mandatory if acute intracranial process suspected (new neurologic signs, severe headache, altered mental status) 4, 5

Specialized Testing for Chronic Symptoms (>1 month)

• Esophagogastroduodenoscopy (EGD) - for patients with alarm features (weight loss, dysphagia, GI bleeding) or risk factors for gastric malignancy; avoid repeated studies 8, 5
• Gastric emptying scintigraphy - the gold standard for gastroparesis diagnosis, must be performed for 4 hours (not 2 hours) with radioisotope cooked into solid meal; do NOT order during acute CVS episodes or in patients actively using cannabis/opiates as results are uninterpretable 1, 8
• Antroduodenal manometry - provides information on gastric-duodenal motor coordination when gastroparesis suspected but emptying study normal 1

Common Pitfalls to Avoid

1. Assuming hot water bathing equals CHS - This behavior occurs in CVS without cannabis use 8
2. Ordering gastric emptying studies too early - Results during acute episodes or with confounding medications are meaningless 8
3. Repeating EGD unnecessarily - Recognize epiphenomena of recent vomiting (mild gastritis, Mallory-Weiss tears) as effects, not causes 8
4. Missing opioid-induced constipation as nausea cause - Always assess bowel function in patients on opioids 6, 3
5. Overlooking psychiatric comorbidities - Anxiety and depression are present in 50-60% of CVS patients and may contribute to functional nausea 8