REASONING GP · Clinical algorithm · Quick reference

Nausea and vomiting in adults — triage and diagnosis

Daytime GP and OOH/111, face-to-face or remote. The diagnosis lies in what the vomiting comes with, not in the vomiting. Ongoing management is in the full Steps pathway.
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AdultsGP + OOHCause firstv1.0 · Sep 2026
Core rule. Urine β-hCG in every woman of reproductive age before investigating or prescribing. Then classify by the accompanying feature: vomiting with headache, with abdominal pain, with vertigo, or with thirst and weight loss are four different problems. Never treat persistent vomiting with an antiemetic alone — failure of a correctly chosen antiemetic is a diagnostic statement, not a reason to add a second drug.
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Before any history: is this an emergency now? Stop the consultation and call 999 if any of these is present
Rigid, guarded abdomen or peritonism · haematemesis or coffee-ground vomit with compromise · thunderclap headache · reduced or fluctuating consciousness, or new confusion · seizure · ketosis with Kussmaul breathing in diabetes · shock or postural hypotension · chest pain or sweating · non-blanching rash with fever. ABCDE, observations, nil by mouth, IV access. Capillary glucose and ketones in anyone with diabetes. Do not delay transfer for bloods, an antiemetic or imaging.
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Define the vomiting in four lines Enough to place the patient in the table below

Time

Acute <1 week or chronic >1 month. Timing: early morning before eating (pregnancy, raised ICP, alcohol, uraemia) · 1–3 hours after eating (gastroparesis or outlet obstruction) · during eating (functional).

Character

Bile (pylorus patent, obstruction distal) · undigested food hours later (gastric stasis or outlet obstruction) · faeculent (distal obstruction or fistula) · blood or coffee-grounds (upper GI bleed route). Effortless regurgitation without nausea is not vomiting (achalasia, rumination).

Context

Pregnancy · diabetes/insulin · long-term steroids · drugs (opioids, GLP-1 agonists, chemotherapy, antibiotics, digoxin, metformin, SSRIs, iron, colchicine, levodopa — or a recent dose increase) · alcohol, cannabis · previous abdominal surgery · head injury · immunosuppression.

Associated

Pain, and whether vomiting relieves it · bowels: diarrhoea (reassuring) vs absolute constipation with no flatus (obstruction) · headache, visual change, focal neurology · vertigo, hearing change, gait · thirst, polyuria, weight loss · dysphagia · self-induced vomiting, dietary restriction, dental erosion.
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Red-flag screen: trigger → concern → destination → what to do before handover One row is enough; do not add up reassuring features
Trigger / red flagLeading concern · destinationDo now · do not delay
Bilious or faeculent vomiting with distension and absolute constipation (no stool and no flatus); previous abdominal surgery; high-pitched or absent bowel sounds; peritonism. Bowel obstruction · perforation · strangulation
999 / same-day surgical take		 Nil by mouth, IV access; examine hernial orifices and scars. Never give a prokinetic in suspected mechanical obstruction — risk of perforation. Not an outpatient scan: the decision is fluids, NG decompression and imaging within hours.
Vomiting worse on waking or lying flat, with headache; papilloedema; focal deficit; new seizure; visual obscurations; personality or cognitive change; recent head injury on anticoagulants. Raised intracranial pressure · tumour · haemorrhage
999 if acute or deteriorating Urgent direct-access MRI within 2 weeks if sub-acute progressive · NG12		 Do fundoscopy — it changes the disposal. Ask whether vomiting eases when upright; patients rarely volunteer it. Never treat morning vomiting with headache as gastritis.
Thunderclap headache, meningism or non-blanching rash with vomiting. Subarachnoid haemorrhage · bacterial meningitis
999 + pre-alert		 Record exact onset and time-to-peak. Benzylpenicillin 1.2 g IM/IV before transfer if meningococcal disease is strongly suspected and it will not delay the ambulance. Do not attribute a first presentation to migraine.
Diabetes with vomiting: thirst, polyuria, weight loss, Kussmaul breathing, capillary ketones ≥3.0 mmol/L (or unwell with ketones ≥1.5). Or long-term steroids / known adrenal insufficiency, unable to absorb tablets; hypotension, hyponatraemia, hyperkalaemia, pigmentation. Diabetic ketoacidosis · adrenal (Addisonian) crisis
999 now		 Check capillary glucose and ketones in every vomiting person with diabetes; never omit insulin (sick-day rules). SGLT2 inhibitors cause euglycaemic DKA — normal glucose does not exclude it. If steroid-dependent or adrenally insufficient: hydrocortisone 100 mg IM now, then transfer — vomited oral replacement is not absorbed; a crisis develops within hours. Check the steroid card and kit.
Unable to keep any fluid down >24 hours, or drowsy, confused, oliguric, or postural drop >20 mmHg; frail or living alone. Dehydration with AKI, hyponatraemia or hypokalaemia
Same-day admission for IV fluids		 Hypokalaemia both results from and worsens vomiting through ileus — correct it to break the cycle. Suspend nephrotoxics: ACE inhibitors, ARBs, diuretics, metformin, SGLT2 inhibitors.
Pregnancy: hyperemesis with ketonuria or weight loss >5%; any vomiting after 20 weeks with hypertension, epigastric pain, headache or jaundice. Hyperemesis gravidarum · pre-eclampsia · HELLP · acute fatty liver of pregnancy
Urgent maternity assessment 999 if BP ≥160/110 or focal signs		 Speak directly to the maternity unit. Record gestation, weight change, urine ketones and BP. Vomiting starting after the first trimester is not ordinary NVP — find another cause.
Age ≥55 with nausea or vomiting plus weight loss, reflux, dyspepsia or upper abdominal pain; or a raised platelet count. Dysphagia at any age. Oesophageal or stomach cancer
Dysphagia: urgent direct-access OGD within 2 weeks · otherwise consider non-urgent OGD · NICE NG12		 Use the correct threshold: dysphagia at any age is the urgent 2-week route; nausea and vomiting with an additional feature at ≥55 is "consider non-urgent direct-access OGD". Also hypercalcaemia: bone pain and vomiting over 60 → FBC, ESR or plasma viscosity, urine protein electrophoresis (myeloma, NG12).
Safety rule. Repeat a negative pregnancy test if the LMP is uncertain. Gastroenteritis is nearly always improving by 48 hours, so persistence means the working diagnosis was probably wrong — obstruction, raised ICP, DKA, Addison's and hypercalcaemia all masquerade as it for two days. Vomiting with diarrhoea is rarely obstructive; vomiting with absolute constipation usually is. Vomiting with no abdominal signs in an older adult or a person with diabetes can be a silent myocardial infarction — autonomic neuropathy can reduce a coronary event to vomiting alone, so keep the threshold for an ECG very low over 60 or in diabetes, and call 999 with chest discomfort, sweating or breathlessness.
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Focused examination and investigation Only after the emergency question is answered; remote assessment that cannot deliver these is an escalation criterion

Observations

Pulse, BP lying and standing, RR (Kussmaul), SpO₂, temperature, conscious level, capillary refill, weight. Capillary glucose and ketones in diabetes. NEWS2 if unwell.

System examination

Abdomen: distension, visible peristalsis, tenderness, guarding, rebound, masses, hernial orifices, scars, bowel sounds, succussion splash (gastric outlet obstruction). PR for an empty rectum, impaction or melaena.

Targeted signs

Fundoscopy for papilloedema; cranial nerves, limb power, coordination, gait; neck stiffness if febrile. Nystagmus, Dix-Hallpike, head impulse test — standing unaided impossible means a central cause. Buccal and palmar pigmentation; dental erosion, parotid swelling.

Investigations

Urine β-hCG first. Then question-led: FBC, U&Es, LFTs, calcium, glucose or HbA1c, CRP, TFTs, amylase or lipase if epigastric pain; coeliac serology, 9 am cortisol, digoxin level; ECG. Not from primary care: abdominal X-ray, CT, gastric emptying (never before an OGD).
Colour is semantic: red = emergency now · amber = same-day acute assessment · blue = define/assess · green = benign diagnosis established · purple = uncertain / specialist route. Continued on page 2: classification, cause classifier, routine referral, primary-care treatment, endpoint.
REASONING GP · Nausea and vomiting in adults — triage and diagnostic approach
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Classify: three exits, not two "Probably a virus" at 48 hours is a decision to re-examine, not to continue

Serious cause likely

Any red flag, deranged physiology, pregnancy with red flags, or a surgical, neurological or metabolic pattern. Output: name the leading concern, use the destination above, and hand over observations, glucose and ketones, and the drug list.

Self-limiting or reversible cause established

Gastroenteritis with diarrhoea and normal physiology; a clear drug cause with a dose to reduce; a typical vestibular or migraine attack; mild NVP. Output: name the cause, state the expected course, prescribe by mechanism with a review date.

Unclassified / uncertain

Persistent vomiting with no cause, remote assessment, frailty, or failure of a well-chosen antiemetic. Output: do not add a second antiemetic. Return to the history, arrange bloods, and set a defined review — or admit.
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Cause classifier — seven groups The group determines which antiemetic will work
GI and surgicalGastroenteritis (commonest), obstruction, appendicitis, pancreatitis, biliary disease, peptic ulcer, gastric outlet obstruction, gastroparesis (long-standing diabetes), upper GI malignancy.
NeurologicalMigraine (common) · raised ICP from tumour, haemorrhage, hydrocephalus or idiopathic intracranial hypertension · meningitis, encephalitis, SAH, concussion. Acute angle-closure glaucoma presents as headache and vomiting with a red painful eye and a fixed mid-dilated pupil — sight is lost within hours.
VestibularBPPV, vestibular neuronitis, labyrinthitis, Ménière's, vestibular migraine, motion sickness. New gait ataxia in an older vasculopath → posterior circulation stroke.
Metabolic and endocrineDKA, uraemia, hypercalcaemia (vomiting, constipation, thirst, confusion — often the first sign of malignancy or hyperparathyroidism), hyponatraemia, Addison's disease, thyroid disease.
Drugs and toxinsOpioids, GLP-1 receptor agonists (usually a recent dose escalation), chemotherapy, antibiotics, digoxin toxicity, NSAIDs, dopamine agonists, alcohol, carbon monoxide. Cannabinoid hyperemesis: cyclical vomiting in a regular user, relieved by hot showers — cessation is the only treatment.
PregnancyNausea and vomiting of pregnancy and hyperemesis gravidarum (first trimester); after 20 weeks consider pre-eclampsia, HELLP and acute fatty liver of pregnancy.
Functional, psychiatric — and do not label by defaultFunctional nausea and vomiting (Rome IV), cyclical vomiting syndrome, rumination, anxiety, bulimia nervosa. "Gastritis", "a virus" and "stress" need positive evidence and a review date. Also consider inferior MI, renal colic, urinary sepsis and radiotherapy.
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Refer routinely from this consultation Not same-day, not 999 — the cases that leave by letter
Routine gastroenterology: chronic unexplained nausea or vomiting after negative first-line investigation; suspected gastroparesis (only after mechanical obstruction has been excluded endoscopically — a gastric emptying study is never the first test); suspected functional or cyclical vomiting syndrome; suspected achalasia. Routine endocrinology: confirmed hypercalcaemia or suspected Addison's once acutely stable. Eating disorder service — urgently if there are physical risk markers (bradycardia, hypotension, hypokalaemia): self-induced vomiting, dietary restriction or dental erosion. Interim advice: oral rehydration in small frequent sips, a short defined antiemetic course with a stop date, and the written safety-net below. Not routine: dysphagia at any age (urgent 2-week OGD) and every page-1 red flag.
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The only treatment decisions that belong in this consultation Choose the antiemetic by receptor, not by habit
Obstruction, raised ICP, DKA, MI, SAH, meningitisTransfer is the treatment. Nil by mouth, IV access if available, oxygen if hypoxic. Do not give a prokinetic in suspected obstruction. Do not sedate; do not request outpatient imaging; do not give an antiemetic instead of arranging admission.
Adrenal crisisHydrocortisone 100 mg IM now, then 999. Any steroid-dependent patient who is vomiting has not absorbed their replacement dose. Double the oral dose during illness; use the emergency kit if vomiting.
Vestibular causeCyclizine 50 mg up to three times daily, or prochlorperazine 5 mg three times daily / 3 mg buccal twice daily. Ondansetron does not work for vestibular nausea. Use for the shortest period — prolonged use delays vestibular compensation.
Gastric stasis / gastroparesis (obstruction excluded)Metoclopramide 10 mg three times daily — maximum 5 days (MHRA 2013), avoid under 20 years and in Parkinson's. Alternative: domperidone 10 mg three times daily, maximum 1 week at the lowest effective dose (MHRA 2014), avoid in cardiac disease or QT prolongation. Issue with a stop date so it cannot become a repeat.
Chemical, metabolic or drug-induced; pregnancy; migraineChemical/metabolic: ondansetron 4–8 mg three times daily (constipation, headache, QT). Pregnancy: cyclizine 50 mg three times daily or promethazine 12.5–25 mg first line (NG126); metoclopramide or ondansetron second line after discussing risks; thiamine if prolonged. Migraine: prochlorperazine or metoclopramide with the triptan or NSAID — the prokinetic also improves absorption.
Route and rehydrationOral rehydration salts, 5 ml every 5 minutes. If oral is not retained, change the route — buccal prochlorperazine, rectal domperidone, or the subcutaneous route in palliative care. An oral tablet that is vomited back has done nothing. Reduce or stop the culprit drug: most drug-induced nausea settles on dose reduction alone.
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Endpoint and documentation Finish with one of four conclusions and a named owner

1 · Time-critical

999 or same-day surgical/medical route taken; suspected diagnosis, observations including postural BP, glucose and ketones, GCS, steroid and insulin status, drugs given with dose and time.

2 · Serious cause possible

Same-day route or targeted test arranged; state the question being excluded, who was spoken to, and the deadline. Record the pregnancy test result and that nil by mouth was advised where relevant.

3 · Reversible cause established

Named cause, the mechanism-matched antiemetic with dose, route, duration and stop date, rehydration plan, sick-day rules where relevant, safety-net, review owner and date.

4 · Unclassified

Uncertainty stated; a second antiemetic not added; the history revisited; investigations arranged and chased by name; 48-hour review booked with explicit escalation criteria.
Why a benign conclusion is safe today, in one line: negative pregnancy test (or pregnancy accounted for) · normal physiology including postural BP, and glucose and ketones where relevant · no absolute constipation, bilious or faeculent vomit, papilloedema or posture-dependent headache · a coherent cause with a mechanism-matched treatment and a stop date · written safety-net given and a 48-hour review agreed. Safety-net wording: call 999 for severe tummy pain with a hard abdomen, vomiting blood, a sudden severe headache, drowsiness or confusion, chest pain, or a fit; contact us the same day if you cannot keep any fluid down, you pass very little urine, you feel dizzy standing up, your headache is worse on waking or lying flat, or you have diabetes and your ketones are raised.
OOH / remote limitation. Convert to face-to-face or emergency assessment if a pregnancy test, observations, postural BP, abdominal examination, fundoscopy, or glucose and ketones cannot be obtained; the vomit content cannot be described reliably; the patient has diabetes, takes steroids, is pregnant, is frail or lives alone; symptoms are changing during the call; or timely review cannot be guaranteed. Under time pressure the default is the safer destination.
Clinical decision support only; follow local emergency-transfer, emergency-medicines and referral policies and check doses against the current BNF. Source hierarchy: NICE guidelines first, then BNF/MHRA for doses and safety, then national specialty guidance. Sources: NICE NG12 Suspected cancer: recognition and referral · CG184 Gastro-oesophageal reflux disease and dyspepsia in adults · NG126 Ectopic pregnancy and miscarriage (context) · NG17 Type 1 diabetes and NG28 Type 2 diabetes (sick-day rules) · NG51 Sepsis · NICE guidance — Nausea and vomiting in adults · BNF · MHRA Drug Safety Update: metoclopramide (2013) and domperidone (2014) · Rome IV criteria for functional gastroduodenal disorders. Review after any guidance or medicines-safety update, otherwise every 6 months. © Reasoning GP · gpreasoning.uk