Cluster Headache

Cluster headache is the most common of the trigeminal autonomic cephalalgias (TACs) -- a group of primary headache disorders that share short-lasting, severe, strictly one-sided pain attacks together with prominent ipsilateral cranial autonomic symptoms.^[1] It is a genuinely different disease from migraine and tension-type headache, not a more severe version of either: the attacks are shorter, far more intense, occur in clustered bouts, and are managed with an entirely different drug list -- high-flow oxygen and injectable/intranasal triptans for an attack, and verapamil as first-line prevention, none of which have a comparable role in migraine or tension-type headache.^[2]

Attacks are excruciating -- among the most severe pain a person can experience -- and the disorder has earned the lay nickname "suicide headache"; a meaningful minority of patients report suicidal ideation during an unremitting bout, which makes deliberate safety screening part of routine assessment, not an afterthought.^[3]

Cluster headache is classified as episodic (ICHD-3 code 3.1.1) -- attacks occurring in bouts lasting days to months, separated by pain-free remission periods of 3 months or longer -- or chronic (ICHD-3 code 3.1.2) -- attacks occurring for more than 1 year without remission, or with remission periods shorter than 3 months. About 80% of patients have the episodic form; up to 12% of episodic patients eventually progress to chronic cluster headache, and rarely a chronic pattern reverts to episodic.^[3]

Pain distribution of the three primary headache types -- cluster headache is the most sharply localized, centred on one eye and temple, unlike the band-like tension headache or the broader one-sided migraine pattern. (Hernandez et al., Journal of Integrative Neuroscience, CC BY 4.0, Wikimedia Commons)

Ptosis of the right eyelid, 27 minutes into a cluster headache attack -- a classic ipsilateral autonomic feature (partial Horner syndrome), alongside the miosis, conjunctival injection, lacrimation, and rhinorrhea also typical of an attack. (Tbjornstad, CC BY-SA 4.0, Wikimedia Commons)

Circadian and circannual pattern

Attacks are frequently nocturnal -- classically waking the patient 1-2 hours after falling asleep -- and bouts often recur at the same time of year (spring or autumn is common), a circannual rhythmicity that is itself a useful diagnostic clue.^[2]

Episodic vs. chronic cluster headache

During an active bout (a "cluster period"), attacks occur in clusters typically lasting 7 days to several months (most often 4-12 weeks), followed by a symptom-free remission of 3 months or longer in the episodic form; during remission, cluster-typical triggers (alcohol, in particular) no longer provoke an attack. In chronic cluster headache -- 15% of all cases -- attacks occur on a near-daily basis without a meaningful remission, or with remission shorter than 3 months.^[3]

• Male sex -- historically estimated at 3-4:1 male-to-female, though the gap has been narrowing over recent decades.^[3]
• Age of onset typically in the 20s-40s (commonly cited peak around 28-30 years).^[2]
• Family history -- a modest genetic component, with cluster headache reported in 2-7% of first-degree relatives of affected patients.^[3]
• Cigarette smoking -- most patients with cluster headache are current or former smokers, one of the strongest and most consistent associations described for this disorder; smoking cessation should be raised, though it should not delay starting effective treatment.^[2]
• Alcohol -- a well-established trigger for attacks, but specifically during an active bout only; the same patient can typically drink alcohol without triggering an attack while in remission, an important and reassuring counselling point.^[3]
• Other vasodilating triggers during a bout -- nitroglycerin/other nitrates, histamine, strenuous exertion, high altitude, and daytime napping have all been reported to provoke attacks in the active period.^[2]
• The underlying mechanism is not fully understood but is thought to involve hypothalamic activation (accounting for the circadian/circannual rhythmicity) together with activation of the trigeminal-autonomic reflex, which produces both the severe first-division trigeminal pain and the ipsilateral parasympathetic (autonomic) features.^[3]

ICHD-3 diagnostic criteria for cluster headache

Differentiating the trigeminal autonomic cephalalgias

Cluster headache, paroxysmal hemicrania, and SUNCT/SUNA share the same basic structure -- short-lasting, strictly unilateral pain with ipsilateral cranial autonomic features -- but differ enough in duration, frequency, and (critically) treatment response that mistaking one for another leads directly to the wrong treatment.

Migraine as a differential

Migraine remains the most important non-TAC differential: migraine pain is typically longer-lasting (4-72 hours untreated), less strictly one-sided, and accompanied by a preference to lie still rather than the restlessness typical of cluster headache; nausea/vomiting and generalized (not lateralized) photophobia/phonophobia are also more typical of migraine. Both conditions can coexist in the same patient, which is itself a recognized contributor to diagnostic delay -- see the separate Migraine chapter for its full diagnostic and treatment detail.^[2]

Investigations

• No laboratory, electrophysiological, or CSF test contributes to the diagnosis of a primary TAC -- diagnosis rests on history and a normal neurologic examination.^[3]
• Brain MRI including the craniocervical junction is recommended for the initial diagnosis of cluster headache, and for any patient with an abnormal neurologic examination or another red flag (see Red Flags & Refer), specifically to exclude a structural secondary cause.^[3]
• A baseline ECG is required before starting verapamil, given its cardiac conduction effects (see Choose Initial Treatment and Monitoring & Follow-Up).^[2]

• Rapidly and reliably terminate individual attacks -- given attack severity, "rapidly acting" is not optional; a slow-onset acute treatment is not an adequate treatment for this disease.
• Suppress attacks entirely and re-establish remission for the expected duration of the bout, using transitional and preventive therapy together rather than acute treatment alone.
• Minimize acute-medication burden and its risks by front-loading effective, non-overusable acute options (oxygen) alongside triptans.
• Detect and manage medication-related complications early -- verapamil's cardiac conduction effects and lithium's narrow therapeutic index both require active, scheduled monitoring, not passive follow-up.
• Screen for and address the psychological burden of the disease, including suicidal ideation during active bouts.
• Taper preventive therapy appropriately once sustained remission is achieved, rather than continuing indefinitely by default in episodic cluster headache, or stopping abruptly in any patient.

• During an active bout specifically, advise avoiding alcohol, nitroglycerin/other vasodilating medications, strenuous exertion, high altitude, and daytime napping -- all recognized attack triggers during the active period, but not necessarily during remission (a genuinely reassuring distinction to make explicit for patients).^[3]
• Teach correct oxygen technique specifically -- a non-rebreather mask at 12-15 L/minute, seated upright, breathing normally for the full 15-20 minutes -- since this simple, highly effective, side-effect-free treatment is frequently used incorrectly (most often with an inadequate-flow nasal cannula) and then wrongly judged to have failed.^[2]
• Smoking cessation counselling, given the strong association between cluster headache and smoking -- but do not delay effective acute/preventive treatment while pursuing it.^[2]
• A headache diary tracking attack frequency, bout onset, and remission is genuinely useful here -- it guides how long to continue preventive therapy and when it is reasonable to begin a taper.
• Non-invasive vagus nerve stimulation (nVNS) has a strong evidence base as an add-on acute treatment in episodic cluster headache (not shown effective for chronic cluster headache acute attacks), and a weaker evidence base as an add-on to standard preventive care.^[3]
• Explicit psychological support and safety screening -- validate the severity of the pain, explain the cyclical/self-limited nature of episodic bouts, and directly ask about mood and suicidal ideation during an active bout rather than waiting for the patient to raise it.^[3]
• For refractory chronic cluster headache that has failed medical therapy, invasive options exist at specialized centres -- sphenopalatine ganglion (SPG) stimulation has a strong evidence base for both acute attack treatment and prevention of chronic cluster headache; occipital nerve stimulation has been studied but has only very-low-quality evidence and no formal recommendation. Both are specialist-directed, not primary-care or community-pharmacy decisions.^[3]

Pregnancy

Breastfeeding

Oxygen and sumatriptan are considered compatible with breastfeeding. Verapamil is generally compatible with monitoring. Lithium transfers into breast milk and carries a real risk of infant toxicity -- avoid, or use only with specialist supervision and infant monitoring.

Cardiac disease and older adults

Verapamil is contraindicated in significant AV block, sick sinus syndrome (without a pacemaker), and decompensated heart failure, and needs particular caution when combined with other rate-limiting or negative-inotropic drugs (beta-blockers, diltiazem); ECG monitoring is especially important in this group. Triptans carry the usual contraindications in significant cardiovascular disease and uncontrolled hypertension. Oxygen has no cardiovascular contraindications, which makes it a particularly valuable first-line option when triptans or verapamil are limited by cardiac disease.^[3]

Renal impairment

Lithium requires more cautious dosing and closer level monitoring in renal impairment given reduced clearance and narrow therapeutic index; verapamil does not require renal dose adjustment and is generally preferred if renal impairment limits lithium use.

Smokers

The great majority of patients with cluster headache are current or former smokers. Raise smoking cessation as part of overall care, but do not delay or withhold effective acute or preventive treatment while addressing it.^[2]

• Verapamil ECG schedule: baseline ECG before starting; repeat ECG once the daily dose reaches 400 mg, and again about a week after every further dose increase beyond that -- continue periodic ECGs on a stable maintenance dose, particularly at doses above 480 mg/day, since arrhythmias can develop even after a period of good tolerance.^[2][3]
• Lithium monitoring: baseline renal and thyroid function before starting; periodic renal/thyroid function and serum lithium trough levels thereafter, targeting 0.4-0.8 mmol/L and never exceeding 1.2 mmol/L. Ask specifically about tremor, GI upset, and confusion at each follow-up as early signs of toxicity.^[2]
• Track attack frequency, bout duration, and remission with a headache diary at every follow-up -- this is what determines both whether preventive therapy is working and when it is reasonable to begin tapering it.
• Once a patient has been in sustained remission beyond their usual bout length, taper verapamil (or lithium) gradually over 2-4 weeks rather than stopping abruptly or continuing indefinitely by default; chronic cluster headache patients may need indefinite preventive therapy, individualized to the patient.^[2]
• Reassess for chronification (progression from episodic to chronic cluster headache, seen in up to 12% of episodic patients) if bouts are becoming longer, more frequent, or remissions shorter over time.^[3]
• Screen for mood and suicidal ideation at follow-up during any active bout, not only at initial diagnosis.^[3]

1. Reconfirm the diagnosis before assuming treatment failure -- recheck ICHD-3 criteria, reconsider paroxysmal hemicrania (consider a supervised indomethacin trial) and SUNCT/SUNA (attacks far shorter and far more frequent, no indomethacin response) if the attack duration or frequency does not fit classic cluster headache.^[2][4]
2. Confirm oxygen was actually delivered correctly -- adequate flow rate (12-15 L/min), a non-rebreather mask (not a nasal cannula), and the full 15-20 minute duration -- before concluding oxygen has failed; incorrect technique is a common, avoidable cause of apparent oxygen failure.
3. Confirm SC sumatriptan (not an oral formulation) was used at an adequate dose before concluding the triptan class has failed; try intranasal zolmitriptan or intranasal sumatriptan as an alternative route before abandoning triptans altogether.
4. For preventive failure, confirm verapamil was actually titrated to a genuinely effective, ECG-cleared dose (commonly 480 mg/day, occasionally higher under cardiology supervision) before switching -- premature step-down to lithium at a low, ineffective verapamil dose is a common and avoidable error.^[2]
5. If verapamil at a maximally tolerated/ECG-cleared dose is inadequate, not tolerated, or contraindicated, add or switch to lithium with baseline and periodic renal/thyroid monitoring and trough-level targeting.
6. For refractory episodic cluster headache, galcanezumab is a licensed add-on option; for refractory chronic cluster headache, consider topiramate or melatonin as add-ons, non-invasive vagus nerve stimulation, or referral for sphenopalatine ganglion stimulation at a specialized centre.^[3]
7. Refer to a headache specialist or neurology for any case of genuine diagnostic uncertainty, failure of two adequately dosed preventive medications, or significant psychophysical distress from drug-refractory attacks.^[3]

• Treating cluster headache as "severe migraine" and reaching for oral triptans or migraine-style stepped analgesia instead of oxygen and an injectable/intranasal triptan -- the two diseases need different drugs.^[2]
• Delivering oxygen through a nasal cannula instead of a non-rebreather mask, or at an inadequate flow rate/duration, and then concluding oxygen "doesn't work" for this patient.
• Using an oral triptan as routine acute therapy -- too slow for the attack's natural course, and only weakly supported by evidence.^[3]
• Starting verapamil without a baseline ECG, or continuing to escalate the dose without the required follow-up ECGs at 400 mg/day and beyond.^[2]
• Stopping an effective preventive (verapamil or lithium) abruptly rather than tapering over 2-4 weeks once sustained remission is achieved.
• Substituting a proven migraine preventive (a beta-blocker, for example) for verapamil on the assumption that any migraine preventive will work in cluster headache -- many do not.^[3]
• Using a prolonged, unpaired course of oral corticosteroids as if it were a maintenance preventive, rather than a short bridge alongside verapamil titration.
• Missing a secondary cause on first presentation by treating an atypical case (abnormal exam, onset after 60, poor response to oxygen/triptan) as routine cluster headache without imaging.^[3]
• Confusing cluster headache with paroxysmal hemicrania or SUNCT/SUNA and prescribing the wrong first-line treatment as a result -- these conditions do not all respond to the same drugs.^[4]
• Not asking directly about suicidal ideation during an active bout.^[3]

How to use this table: Doses are adult doses and require patient-specific confirmation, including cardiac, renal, and hepatic status and pregnancy. Select any drug name to open its complete Pharmasist Drug Database page.

Acute attack -- triptans

Only injectable and intranasal formulations are appropriate for cluster headache -- onset is too slow with oral tablets for a 15-180 minute attack.

Transitional (bridge) therapy

Reserved primarily for high-frequency episodic cluster headache (more than 2 attacks/day); always paired with a maintenance preventive being titrated in parallel, not used alone.

Preventive therapy -- first- and second-line

Verapamil is the preventive of choice; lithium is second-line. Many proven migraine preventives (e.g., beta-blockers) are not effective in cluster headache.

Preventive therapy -- add-on / alternative options (weaker evidence)

Consider when verapamil and lithium are inadequate, not tolerated, or contraindicated; typically specialist-guided.

Evidence note: Drug inventory, dosing, and the verapamil ECG-monitoring protocol reflect Becker's Canadian Headache Society-hosted review^[2] and the 2023 European Academy of Neurology guideline on cluster headache treatment^[3].