Reasoning GP · Algorithm · 1-page summary
Acute headache in adults
For: adults with a new, changed or recurrent headache, in person or remote, in hours or OOH. Not for: children, or ongoing treatment of a diagnosed primary headache (full algorithm, Steps 7–9).
Core rule: a new headache, or a significant change in an established one, is secondary until the evidence says otherwise. A normal examination, a migraine history or improvement excludes no red flag. If safe assessment, transport or follow-up cannot be guaranteed, choose the acute route.
0Stop — call 999 now — before any history
- Thunderclap: sudden severe headache peaking within 1–5 minutes, “worst ever”, or onset with exertion, cough or sex — even if now settled → 999
- GCS <15 or fluctuating, seizure, rapid deterioration, airway/breathing/circulation compromise or sepsis features → 999
- Persistent focal deficit; painful diplopia or III-nerve palsy; fever with neck stiffness; non-blanching rash → 999. Neurology fully resolved → TIA route
- While waiting: ABCDE; record onset, time to peak, last-known-well, anticoagulants. Suspected meningococcal disease → benzylpenicillin 1.2 g IM/IV unless it delays transfer or severe allergy. Do not delay transfer for bloods, CT requests or analgesia.
1Define it in four lines
| Time | New, changed or recurrent? Time to peak? Progressive? |
| Character | Worst ever? Worse with cough, lying flat or on waking? |
| Context | ≥50 · pregnant/postpartum · cancer · HIV/immunosuppressed · anticoagulated · head injury · household unwell (CO) |
| Associated | Fever, stiff neck, rash · visual loss, diplopia, red eye · weakness, speech, confusion · jaw claudication |
2Screen — one row is enough
- Raised ICP / structural: progressive over days–weeks, worse lying flat or waking, vomiting, papilloedema, pulsatile tinnitus; cancer or immunosuppression → Same-day acute; 999 if deteriorating. Anticoagulated head injury → Same-day CT
- GCA: age ≥50, new headache plus jaw claudication, scalp tenderness, visual or PMR symptoms → prednisolone now + Same-day rheum / acute med; visual → Emergency eye
- Angle-closure glaucoma: painful red eye, reduced vision, halos, mid-dilated pupil → Emergency eye unit now
- ≥20 weeks pregnant or ≤6 weeks postpartum: new headache, BP ≥140/90, visual change, epigastric pain → Urgent maternity; 999 if seizure, severe hypertension, reduced consciousness, focal deficit
- Systemic / toxic: BP ≥180/120 with target-organ features; household unwell (CO); new drug or withdrawal → Same-day acute; symptomatic CO → 999
- Progressive sub-acute neurological loss over weeks (personality, cognition, weakness) → NG12 MRI brain ≤2 weeks; papilloedema or rapid progression → Same-day
3Assess — once blocks 0–2 are answered
☐ BP, pulse, temperature, SpO₂, GCS ☐ Cranial nerves, limbs, gait ☐ Acuity, fields; fundi if trained ☐ Neck, rash; temporal arteries if ≥50. ESR/CRP for GCA; never delay steroids. CT/LP via hospital. No imaging for a typical primary pattern.
4Classify — only if the screen is negative
- Migraine — ≥5 attacks, 4–72 h; ≥2 of unilateral, pulsating, moderate–severe, worse with activity; nausea/vomiting or photo- and phonophobia.
- Aura — gradual, fully reversible, 5–60 min. Motor, diplopia, monocular loss, ataxia, >60 min or first-ever → block 2. On combined hormonal contraception → stop it (UKMEC 4).
- Tension-type — ≥2 of bilateral, pressing, mild–moderate, no nausea. Cluster — strictly unilateral orbital, 15–180 min, autonomic features, restless.
- Medication overuse — ≥15 days/month for >3 months; triptan, opioid, ergot or combination analgesic ≥10 days/month, simple analgesic ≥15.
- Uncertain — do not default to “migraine” or “tension”; state exclusions outstanding; review in 1–2 weeks with a diary.
5Treat today — doses: SPC, local formulary
- Suspected GCA: prednisolone (not enteric-coated) 40–60 mg daily before bloods return; visual loss: IV methylprednisolone 0.5–1 g up to 3 days, or 60 mg oral if no IV.
- Secure migraine, no red flags: oral triptan (sumatriptan 50–100 mg) plus NSAID or paracetamol; consider an antiemetic. No opioids or ergots. No triptan in IHD, uncontrolled hypertension or hemiplegic/brainstem aura. Pregnancy: paracetamol first.
- Known cluster attack: 100% oxygen 12–15 L/min via non-rebreather and/or SC or nasal triptan; no oral triptans.
- Everything else serious: transfer is the treatment; no oral BP lowering, no sedation.
6Refer routinely — Routine neurology
- Diagnosis uncertain after a headache diary; suspected cluster, first presentation.
- Overuse headache not resolving after withdrawal; migraine failing two preventives.
7Never reassure by
- Response to analgesia, a triptan, sleep or reassurance.
- “Known migraineur” — the change from the usual pattern is the red flag.
- A thunderclap or “sentinel” headache that has now settled.
- A normal examination, fundal view or ESR (GCA).
- Calling atypical neurology “aura” (aura is gradual, 5–60 min, fully reversible, not motor).
- A “sinus”, “hypertension”, “cervicogenic” or “eye-strain” label without coherent localising findings.
8Safety-net — say it, write it down, document it
999 “Call 999 for a sudden worst-ever headache, weakness, speech or vision change, drowsiness, a seizure, or fever with a stiff neck or rash.” Same day: “Contact us today for new visual symptoms, jaw pain on chewing, a headache that changes character or worsens despite treatment, or a new headache in pregnancy, cancer or low immunity.”
Remote or OOH: convert to face-to-face or emergency care if onset is unclear, examination cannot be done, symptoms change during the call, the caller is not the patient, transport is unreliable or review cannot be guaranteed.
✓Safe to leave primary care only if — all five, documented
No block 0–2 row applies
Normal relevant examination, including neurology and fundi
Stable, coherent phenotype, or uncertainty stated
Analgesic and triptan days/month reviewed
Written safety-net given; review owner and date agreed
Summary of the full Reasoning GP headache algorithm, which holds the history, examination, ICHD-3 criteria, drug ladder and follow-up. Sources: NICE CG150, NG228, NG128, NG240, NG232, NG136, NG133, NG127, NG12 (updated April 2026); BSR GCA guideline 2020; ICHD-3; CoSRH UKMEC; MHRA. Clinical reference — follow local emergency-transfer policies and check doses: SPC, local formulary.