REASONING GP · Clinical algorithm · Quick reference

Acute headache in adults — triage and diagnostic approach

Daytime GP and OOH/111 face-to-face or remote. Screen for time-critical secondary headache, act while transfer is arranged, then classify. Ongoing treatment of each diagnosis is in the full Steps pathway.
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AdultsGP + OOHDiagnosis firstv1.2 · Sep 2026
Core rule. Do not diagnose a primary headache until secondary headache has been actively considered and the red flags below excluded. A new headache, or a significant change in an established one, is secondary until the evidence says otherwise. A normal examination, prior migraine history or symptom improvement does not exclude any red flag. If safe assessment, transport or follow-up cannot be guaranteed, choose the acute-care route.
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Before any history: is this an emergency now? Stop the consultation and call 999 if any of these is present
Reduced or fluctuating consciousness (GCS <15) · seizure · rapidly deteriorating · airway/breathing/circulation compromise or sepsis features · non-blanching rash · persistent focal deficit · thunderclap onset. ABCDE and observations, document exact onset time and last-known-well, hand over. Do not delay transfer for bloods, CT requests, analgesia or a fuller history.
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Define the headache in four lines Enough to place the patient in the table below

Time

First ever, new, changed or recurrent? Exact onset and time to peak (seconds / minutes / hours / days). Continuous or episodic. Progressive or stable.

Character

Side, site, quality, severity, worst ever? Worse with movement, cough, Valsalva, lying flat, on waking.

Context

Age ≥50 · pregnancy/postpartum · cancer · immunosuppression/HIV · anticoagulants · recent head injury · household others unwell (CO) · substances/alcohol · analgesic and triptan days per month.

Associated

Fever, neck stiffness, rash · visual loss, diplopia, halos, red eye · weakness, speech, balance, confusion · vomiting · jaw claudication, scalp tenderness · autonomic features.
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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
Thunderclap: sudden severe headache typically peaking within 1–5 minutes (NG228); "worst ever"; first severe headache; onset with exertion, cough or sex; or abrupt major change in pattern — even if now settling. SAH / intracranial haemorrhage / CVST / dissection
999 now		 Record exact onset and time-to-peak in the patient's words. Observations, GCS. Analgesia may be given but must not delay transfer; document it. A settled "sentinel" headache still goes in: CT accuracy is highest within 6 h; a later negative CT needs LP ≥12 h after onset.
New neurological dysfunction: focal weakness, facial droop, dysphasia, visual loss, diplopia, ataxia, confusion, cognitive change, seizure, drowsiness. Stroke / TIA / CVST / space-occupying lesion / encephalitis
999 if persistent TIA route if resolved		 FAST, last-known-well time, anticoagulant status. Do not attribute atypical neurology to migraine aura (aura is gradual, 5–60 min, fully reversible, not motor). Painful diplopia or III-nerve palsy = aneurysm until proven otherwise → 999.
Infection / meningism: fever with neck stiffness, photophobia, non-blanching rash, altered mental state or seizure; rapid deterioration. Bacterial meningitis / meningococcal disease / encephalitis
999 + pre-alert		 ABCDE, observations. Strongly suspected meningococcal disease (non-blanching rash): ceftriaxone 2 g IV/IM (preferred) or benzylpenicillin 1.2 g IV/IM as soon as possible unless it delays transfer. Suspected bacterial meningitis without rash: give only if transfer will be significantly delayed (NG240). Never delay the ambulance for the injection.
Raised / altered intracranial pressure or structural cause: progressive over days–weeks; worse on waking, lying flat, cough/Valsalva; unexplained vomiting; papilloedema or visual obscurations; pulsatile tinnitus; personality change; new headache with cancer, immunosuppression/HIV, or recent head injury on anticoagulants. Tumour / metastasis / subdural / IIH / CNS infection in immunocompromised
Same-day acute assessment 999 if deteriorating		 Fundoscopy (or same-day eye service if not competent); full neurology. Emergency transfer if focal deficit, seizure, reduced consciousness or rapid progression. Head injury: apply NG232 CT criteria — anticoagulated + head injury = same-day CT. Do not substitute routine imaging or 2WW for same-day assessment when features are acute.
Progressive, sub-acute loss of central neurological function with headache — stepwise or steadily worsening over weeks: personality or cognitive change, progressive focal weakness, dysphasia, ataxia, visual field loss, new seizure in an adult. Not acute (that is the row above). Brain or CNS tumour
Urgent direct-access MRI brain within 2 weeks — CT if MRI contraindicated · NICE NG12		 Request the scan on the urgent suspected-cancer route and state the progressive deficit in the request. Papilloedema, rapid progression or reduced consciousness makes it a same-day admission, not a 2-week scan. A normal scan with a progressing deficit still needs neurology.
Age ≥50 with new headache plus jaw claudication, scalp/temporal tenderness, transient or fixed visual loss, diplopia, PMR symptoms, malaise. Giant cell arteritis
Same-day rheum / acute med Emergency eye if visual		 Start prednisolone now, not enteric-coated: 40–60 mg daily (minimum 0.75 mg/kg) without visual symptoms; 60 mg immediately plus same-day ophthalmology if any visual symptom (NICE CKS/BSR). Do not wait for ESR/CRP or biopsy. Normal ESR does not exclude GCA.
Painful red eye with reduced vision, halos, nausea/vomiting, fixed mid-dilated cloudy pupil. Acute angle-closure glaucoma
Emergency eye unit		 Sight is lost within hours. No investigations in primary care; phone the eye unit and send directly.
Pregnancy ≥20 weeks or up to 6 weeks postpartum: new headache, BP ≥140/90, visual disturbance, epigastric pain, oedema, proteinuria, or focal signs. Pre-eclampsia / eclampsia / CVST / PRES
Urgent maternity assessment 999 if BP ≥160/110, seizure or focal signs		 Record BP, gestation or postpartum interval, urine protein if available. Speak directly to the maternity unit; do not send to routine GP or midwife follow-up. Note that oral contraception, postpartum state and dehydration raise CVST risk.
Systemic / toxic: BP ≥180/120 with headache and acute target-organ features (retinal haemorrhage, papilloedema, chest pain, confusion, AKI); household members with headache/nausea that improves away from home; new drug or withdrawal. Hypertensive emergency / carbon monoxide / drug or substance cause
Same-day acute assessment		 Repeat BP after rest; check fundi, neurology, chest. Do not treat hypertensive emergency with oral drugs in primary care; transfer. Suspected CO: remove from source, 999 if symptomatic, advise not to return home until checked.
Safety rule. Responding to analgesia, a triptan, sleep or reassurance proves nothing. "Known migraineur" is a context, not an exclusion: the change from their usual pattern is the red flag. If any row applies and the safe destination is not available in your setting, escalate rather than observe.
Colour is semantic: red = emergency now · amber = same-day acute assessment · blue = define/assess · green = primary phenotype established · purple = uncertain / specialist route. Continued on page 2: classification, phenotype classifier, routine referral, primary-care treatment, endpoint.
REASONING GP · Acute headache in adults — triage and diagnostic approach
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Focused examination Only after the emergency question is answered; remote assessment that cannot deliver these is an escalation criterion

Observations

BP (both arms if severe), pulse, temperature, RR, SpO₂, GCS, appearance. Hypertension with papilloedema or neurology is an emergency, not a "hypertension headache".

Neurological and visual

Speech, pupils, cranial nerves incl. eye movements, limb power/sensation, coordination, gait if safe. Acuity and fields by confrontation. Fundi: disc margins, venous pulsation, haemorrhage.

Targeted

Neck stiffness, Kernig's; rash; temporal artery tenderness/pulsation and scalp; eye redness and pupil; signs of head injury (Battle's, panda eyes, CSF leak); pericranial and neck tenderness.

Investigations

Only to answer a defined question. ESR/CRP for GCA (never delay steroids). CT/LP for SAH, focal signs, raised ICP, first seizure, immunosuppressed: hospital pathway, not GP-requested. No imaging for a typical primary pattern with normal examination.
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Classify: three exits, not two A normal scan or a history of recurrence does not by itself establish migraine

Secondary headache likely

Any red flag, abnormal examination, high-risk context, or phenotype inconsistent with a stable primary headache. Includes localising causes (eye, ENT/sinus, dental/TMJ, cervical) only when history and examination support a causal link. Output: name the leading concern; use the destination in the table above.

Primary headache likely

Recurrent stable phenotype, no red flags, normal relevant examination, and a recognised pattern from the classifier below. Output: record the phenotype, frequency, and acute-medicine days/month; hand over to the management pathway.

Unclassified / uncertain

First presentation, atypical or evolving features, incomplete examination, mixed phenotype, or no coherent pattern. Output: do not default to "migraine" or "tension". State the uncertainty, the exclusions outstanding, and who reviews when.
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Primary-headache phenotype classifier (ICHD-3) Use only once secondary causes are reasonably excluded
Migraine without aura≥5 attacks, 4–72 h; ≥2 of unilateral, pulsating, moderate–severe, worse with routine activity; plus nausea/vomiting or both photo- and phonophobia. Patient prefers dark and stillness.
Migraine with typical aura≥2 attacks; fully reversible visual, sensory or speech symptoms spreading gradually over ≥5 min, each lasting 5–60 min, headache within 60 min. Not typical aura — return to the red-flag screen: motor weakness, diplopia, monocular visual loss, ataxia, reduced consciousness, aura >60 min, first-ever aura, or aura on combined hormonal contraception (stop the CHC: UKMEC 4).
Tension-typeEpisodes 30 min–7 days; ≥2 of bilateral, pressing/tightening, mild–moderate, not worsened by activity; no nausea or vomiting. Chronic if ≥15 days/month for >3 months — then screen hard for medication overuse.
Cluster / trigeminal autonomic≥5 attacks of severe strictly unilateral orbital/temporal pain, 15–180 min, with ipsilateral lacrimation, red eye, ptosis, miosis, rhinorrhoea, and/or restlessness; often nocturnal, in bouts. New Horner's with neck pain → dissection until excluded.
Medication-overuse headacheSecondary headache: ≥15 headache days/month for >3 months in a pre-existing headache disorder with triptan, opioid, ergot or combination analgesic on ≥10 days/month, or paracetamol/aspirin/NSAID on ≥15 days/month. Ask about OTC, codeine combinations and caffeine.
Do not label by default"Sinus", "hypertension", "cervicogenic" and "eye-strain" headaches need coherent localising findings. New daily persistent headache (daily from a remembered date, >3 months) and IIH (papilloedema, obese young woman, pulsatile tinnitus) need imaging and specialist review: papilloedema is same-day, not routine.
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Refer routinely from this consultation Not same-day, not 999 — the cases that leave by letter
CG150 — diagnosis uncertain after review with a headache diary · suspected cluster headache, first presentation, for confirmation and preventive treatment · medication-overuse headache not resolving after withdrawal · migraine failing two preventives → routine neurology. Not routine: progressive sub-acute loss of central neurological function goes on the NG12 two-week-wait route — urgent direct-access MRI brain (CT if MRI contraindicated) within 2 weeks, and a new red flag uses the page-1 table. What remains below is what primary care treats today.
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The only treatment decisions that belong in this consultation What primary care treats today; everything else is in the management pathway
Meningococcal disease (rash)Ceftriaxone 2 g IV/IM (preferred) or benzylpenicillin 1.2 g IV/IM before transfer if it will not delay the ambulance; not if severe allergy to either. Bacterial meningitis without rash: only if transfer is significantly delayed (NG240). Record drug, dose and time.
Suspected GCAPrednisolone (not enteric-coated) now: 40–60 mg daily, minimum 0.75 mg/kg; 60 mg immediately if visual symptoms, with same-day ophthalmology. Start before bloods return; gastro- and bone-protection per local pathway; note diabetes.
Thunderclap, stroke, glaucoma, raised ICP, hypertensive emergencyTransfer is the treatment. Analgesia is permitted if it does not delay transfer (document it); do not sedate; do not lower BP acutely with oral drugs; no LP or CT requests from primary care.
Established migraine, severe attack (diagnosis already secure, no red flags)CG150 first line: oral triptan (sumatriptan 50–100 mg) plus an NSAID or paracetamol; monotherapy alternatives: triptan, NSAID, aspirin 900 mg or paracetamol. Consider an antiemetic even without nausea (metoclopramide 10 mg, max 5 days per MHRA; or prochlorperazine). Vomiting: SC sumatriptan 6 mg or non-oral antiemetic plus non-oral NSAID/triptan. No ergots or opioids. Triptans contraindicated in IHD, uncontrolled hypertension, hemiplegic/brainstem aura. Pregnancy: paracetamol first; sumatriptan or an NSAID (not third trimester) only after discussing risks.
Known cluster headache, attackCG150: 100% oxygen 12–15 L/min via non-rebreather mask (home oxygen via HOOF, not FP10) and/or SC or nasal sumatriptan/nasal zolmitriptan. No oral triptans, paracetamol, NSAIDs, opioids or ergots for attacks. Verapamil prevention is a specialist decision.
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Endpoint and documentation Finish with one of four conclusions and a named owner

1 · Time-critical secondary

999/emergency route taken; suspected diagnosis, exact onset, time-to-peak, observations, GCS, anticoagulants, any drug given and time.

2 · Secondary possible

Same-day pathway or targeted test arranged; state the question being excluded, who you spoke to, and the deadline by which the patient must be seen.

3 · Primary phenotype established

Phenotype, frequency, acute-medicine days/month, atypical features considered and why they do not apply; onward management pathway.

4 · Unclassified

Uncertainty stated; exclusions outstanding; review owner and timeframe (usually within 1–2 weeks with a diary); explicit escalation criteria.
Why a primary diagnosis is safe today, in one line: no red flags on the page-1 screen · normal relevant examination including fundi and neurology · stable, coherent phenotype · medication days reviewed · written safety-net given and an agreed review. Safety-net wording: call 999 for sudden worst-ever headache, weakness, speech or visual change, drowsiness, seizure, fever with stiff neck or rash; same-day contact for new visual symptoms, jaw pain on chewing, headache changing character, worsening despite treatment, or new headache in pregnancy, cancer or immunosuppression.
OOH / remote limitation. Convert to face-to-face or emergency assessment if onset or time-to-peak is unclear; observations, neurological, visual or fundal examination cannot be obtained; symptoms are changing during the call; the caller is not the patient and cannot describe them; communication or transport is unreliable; 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 and CKS first, then BNF/MHRA for doses and safety, then national specialty guidance. Sources: NICE CG150 Headaches in over 12s · NG228 aneurysmal SAH · NG128 stroke and TIA · NG240 bacterial meningitis and meningococcal disease · NG232 head injury · NG136 hypertension · NG133 hypertension in pregnancy · NG127 suspected neurological conditions · NG12 suspected cancer · NICE CKS Giant cell arteritis · BNF · MHRA (metoclopramide, topiramate) · ICHD-3 · BSR GCA guideline · FSRH UKMEC. Review after any guidance or medicines-safety update, otherwise every 6 months. © Reasoning GP · gpreasoning.uk