CLINICAL PRINTABLE
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A one-page Nausea / Vomiting clinical reference is on the way.
1 · Recognition / Alarm Features
- Acute nausea/vomiting (<1 week): most commonly viral gastroenteritis, medication side effect, or food-borne illness. Subacute or chronic (>1 month): gastroparesis, GERD, peptic ulcer disease, pregnancy, metabolic causes, or CNS pathology.
- Alarm features requiring urgent evaluation: projectile vomiting (suggests increased intracranial pressure), vomiting with severe headache or neck stiffness, hematemesis or coffee-ground emesis, signs of bowel obstruction (abdominal distension, high-pitched bowel sounds, obstipation), or vomiting with chest pain (consider MI, aortic dissection).
- Timing and character: vomiting immediately after eating suggests psychogenic or pyloric obstruction. Vomiting 1–8 hours after eating suggests food-borne toxin (S. aureus, B. cereus). Vomiting >8 hours after eating suggests viral gastroenteritis or C. perfringens. Bilious vomiting suggests obstruction distal to the pylorus.
- Medication causes: opioids (most common), chemotherapy, antibiotics (especially erythromycin, metronidazole), NSAIDs, digoxin toxicity, theophylline toxicity, iron supplements, metformin. Review the medication list at every visit.
- Metabolic causes: DKA (nausea/vomiting + anion gap acidosis), hypercalcemia ('bones, stones, groans'), uremia (CKD stage 4–5), adrenal insufficiency, hyponatremia. Check electrolytes, glucose, BUN/creatinine, and calcium when the cause is not obvious.
2 · Differential / Secondary Causes
Viral gastroenteritis
Most common cause of acute nausea/vomiting. Norovirus, rotavirus. Associated diarrhea, low-grade fever, myalgias. Self-limited 1–3 days. Oral rehydration. No antiemetics required for mild cases.
Gastroparesis
Delayed gastric emptying without mechanical obstruction. Nausea, vomiting of undigested food, early satiety, bloating. Most common in diabetes (autonomic neuropathy) and post-surgical. Gastric emptying study for diagnosis. Metoclopramide or domperidone. Dietary modification (small, frequent, low-fat, low-fiber meals).
Bowel obstruction
Small bowel obstruction (SBO): crampy abdominal pain, nausea, vomiting (bilious if high obstruction), obstipation, distension. Abdominal X-ray (air-fluid levels, dilated loops) or CT abdomen. NGT decompression. Surgery for complete or strangulated obstruction.
Increased intracranial pressure
Projectile vomiting without nausea, severe headache, papilledema, altered mental status. Causes: intracranial hemorrhage, mass lesion, meningitis, hydrocephalus. Urgent CT head. Do not delay imaging for antiemetics.
Cannabinoid hyperemesis syndrome (CHS)
Cyclic vomiting in chronic cannabis users. Compulsive hot bathing (pathognomonic). Resolves with cannabis cessation. Capsaicin cream (topical) and haloperidol are effective acutely. Ondansetron is often ineffective.
3 · Treatment Pathway
Treat the underlying cause first
Antiemetics treat the symptom — they do not treat the cause. Before prescribing an antiemetic, identify and address the underlying etiology. Stopping an offending medication, correcting DKA, or treating bowel obstruction is more important than symptom control.
Oral rehydration and diet
Clear liquids initially, advance as tolerated. Small, frequent meals. Avoid high-fat, high-fiber foods acutely. IV fluids for severe dehydration or inability to tolerate oral intake.
Antiemetics — first-line agents
Ondansetron (5-HT3 antagonist): first-line for most causes. Effective, well-tolerated. Promethazine: effective but sedating; avoid in outpatient settings requiring alertness. Prochlorperazine: effective for nausea/vomiting and migraine-associated nausea. Metoclopramide: prokinetic; useful for gastroparesis and post-operative nausea.
Chemotherapy-induced nausea/vomiting (CINV)
Highly emetogenic regimens require prophylaxis: ondansetron + dexamethasone + NK1 receptor antagonist (aprepitant or fosaprepitant) + olanzapine for highly emetogenic chemotherapy. Anticipatory nausea: lorazepam. Delayed CINV: dexamethasone + NK1 antagonist.
Pregnancy-related nausea/vomiting
Nausea/vomiting of pregnancy (NVP): vitamin B6 (pyridoxine) ± doxylamine is first-line. Ginger supplementation. Ondansetron for refractory cases (avoid in first trimester if possible). Hyperemesis gravidarum (severe NVP with weight loss >5%, ketonuria): IV fluids, thiamine, antiemetics, hospitalization.
4 · Expected Response
- Viral gastroenteritis: self-limited, resolves in 1–3 days with supportive care.
- Ondansetron: onset within 30 minutes. Effective for most acute causes. Does not treat the underlying etiology.
- Gastroparesis: symptom control with dietary modification and prokinetics. Refractory cases may require gastric electrical stimulation or jejunal feeding.
- Medication-induced nausea: resolves within days of stopping the offending agent. Opioid-induced nausea typically improves after 1–2 weeks as tolerance develops.
5 · Escalation
- Hematemesis or coffee-ground emesis: upper GI bleed until proven otherwise. IV access, type and screen, urgent GI consultation. See GI Bleed Deep Dive.
- Projectile vomiting with severe headache, papilledema, or altered mental status: urgent CT head to evaluate for intracranial pathology.
- Signs of bowel obstruction (distension, obstipation, high-pitched bowel sounds, air-fluid levels on X-ray): NGT decompression, surgical consultation.
- Severe dehydration, electrolyte abnormalities, or inability to maintain oral intake: IV fluids, electrolyte repletion, hospital admission.
Apply It · Change One Detail
APPLY IT
A 28-year-old with type 1 diabetes presents with 2 days of nausea, vomiting, and abdominal pain. Glucose is 420 mg/dL, bicarbonate is 12 mEq/L, anion gap is 22. This is DKA — the nausea and vomiting are symptoms of the metabolic emergency, not a primary GI problem. Treat the DKA with IV fluids, insulin, and electrolyte repletion. Antiemetics are supportive only. Do not anchor on GI causes without checking glucose and metabolic panel.
CHANGE ONE DETAIL
Change one detail — a 45-year-old chronic cannabis user presents with cyclic vomiting and is found compulsively taking hot showers. This is cannabinoid hyperemesis syndrome. Ondansetron is often ineffective. Haloperidol 2.5–5 mg IV or topical capsaicin cream are more effective acutely. The definitive treatment is cannabis cessation. Do not escalate antiemetics without recognizing this syndrome.
Bottom Line
Nausea and vomiting are symptoms — always identify the cause before reaching for an antiemetic. Alarm features (hematemesis, projectile vomiting with headache, signs of obstruction) require urgent evaluation, not symptom management.
EVIDENCE & REFERENCES
- Quigley EM, et al. AGA Technical Review on Nausea and Vomiting. Gastroenterology. 2001;120(1):263-286. doi:10.1053/gast.2001.20516
- Hasler WL. Gastroparesis: pathogenesis, diagnosis and management. Nat Rev Gastroenterol Hepatol. 2011;8(8):438-453. doi:10.1038/nrgastro.2011.116
- Hesketh PJ, et al. Antiemetics: ASCO Guideline Update. J Clin Oncol. 2020;38(24):2782-2797. doi:10.1200/JCO.20.01296