Reviews/Anti CGRP Antibodies/Anti-CGRP antibodies for chronic cluster headache
Cluster Headache · CGRP-CH-02 · v2
Two carefully designed, placebo-controlled trials tested whether antibodies that block the CGRP pathway can prevent attacks in people with the chronic form of cluster headache, and both failed to beat placebo on their main measure [12] [20]. The one study showing a benefit in chronic patients was a look-back at records from a small group of hard-to-treat people with no placebo comparison, so its apparent effect is easy to overstate [19]. A separate trial did work, but it was in episodic cluster headache, a related but different condition, and cannot be carried over to the chronic form [6]. Laboratory-style work confirms that CGRP can trigger attacks in chronic patients, which explains why the idea was worth testing, but triggering an attack is not the same as preventing one [13]. Weighing controlled trials against uncontrolled or off-condition signals, the panel found the direct evidence pointed against the claim.
The two controlled trials that directly test the claim both missed their primary endpoint: galcanezumab reduced weekly attacks by -5.4 versus -4.6 for placebo (p=0.334, n=237) [12], and erenumab reduced attacks by -7.3 versus -5.9 per week (group difference -1.5, 95% credible interval -5.7 to 2.8, n=81), with the 50% responder rate numerically favouring placebo (31.7% vs 45.0%) [20]. The only supportive chronic-condition data is a retrospective, uncontrolled case series of 22 refractory patients in which 55% were 50% responders [19]. A galcanezumab trial in episodic cluster headache was positive (difference 3.5 attacks per week, 95% CI 0.2 to 6.7, P=0.04) but concerns a distinct disorder [6]. CGRP infusion provoked attacks in 7 of 14 chronic patients versus none on placebo (P=.02), establishing mechanism rather than preventive efficacy [13]. The contested point: The division is whether the positive signals carry any weight against two negative controlled trials: the uncontrolled case series [19] and the episodic-population trial [6] both favour the antibodies, while the chronic-condition RCTs [12] [20] do not. The panel treated the controlled chronic-headache evidence as decisive and the positive signals as low-quality or from the wrong population.
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
Two pivotal randomized controlled trials in chronic cluster headache — galcanezumab [12] (n=237, p=0.334) and erenumab [20] — both failed their primary endpoints, directly contradicting the claim with gold-standard evidence.
The only positive chronic-CH evidence [19] is a retrospective, uncontrolled, open-label case series in refractory patients, subject to regression to the mean, selection and expectation bias with no placebo comparator.
Where it remains uncertain. The only favourable chronic-condition data is an uncontrolled case series [19], and the one positive controlled trial [6] is in episodic cluster headache, a distinct disorder.
Aleatory
Both chronic-headache trials were modest in size and [20] stopped recruitment early (n=81), so attack-frequency estimates carry wide intervals (95% CrI -5.7 to 2.8) [20].
Epistemic
[20] was underpowered after early stoppage, so the corpus lacks a fully powered second controlled test in the chronic form [20].
The load-bearing papers from a corpus of 38, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Positive in EPISODIC cluster headache only; cannot be extrapolated to chronic, where trials failed.
“The mean reduction in the weekly frequency of cluster headache attacks across weeks 1 through 3 was 8.7 attacks in the galcanezumab group, as compared with 5.2 in the placebo group (difference, 3.5 attacks per week; 95% confidence interval, 0.2 to 6.7; P = 0.04).”
Panel auditInternal validity: medium · scope of inference: Episodic cluster headache prevention across weeks 1-3.Key limitations: episodic not chronic cluster headache · underpowered, enrolment halted early
Mechanistic support for CGRP role in chronic CH; does not test antibody prevention.
“Calcitonin gene-related peptide-induced attacks occurred in 7 of 14 patients with chronic cluster headaches (mean, 50%; 95% CI, 20-80) compared with none after placebo (P = .02).”
Panel auditInternal validity: medium · scope of inference: Whether CGRP infusion provokes attacks in episodic and chronic cluster headache.Key limitations: provocation not prevention · small subgroups (14 chronic)
Only positive chronic-CH signal, but uncontrolled retrospective case series with high bias risk.
“Under real-world conditions, individual treatment with calcitonin gene-related peptide(-receptor) antibodies was effective in 55% of our chronic cluster headache patients.”
Panel auditInternal validity: low · scope of inference: Real-world off-label antibody use in refractory chronic cluster headache patients.Key limitations: no control group · retrospective · small n=22 · highly refractory selected sample
Adequately recruited phase 3 RCT in chronic CH refuting prevention efficacy.
“The primary endpoint was not met; mean change in weekly attack frequency was -4.6 placebo versus -5.4 galcanezumab ( p = 0.334). Key secondary endpoints also were not met.”
Panel auditInternal validity: high · scope of inference: Prevention of chronic cluster headache attacks over a 12-week double-blind period.Key limitations: concomitant preventive medications allowed in 63%
4 of 38 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Two independent negative RCTs directly against the claim outweigh uncontrolled and off-population positive signals.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Adequately powered confirmatory RCT in chronic cluster headache. The only non-futile direct test [12] is a single negative trial and [20] was underpowered, leaving the claim without a confirmatory controlled result. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A fully enrolled, placebo-controlled randomized trial of a CGRP-pathway antibody in chronic cluster headache meeting its planned sample size.
Open question: Does a CGRP-pathway antibody prevent attacks in chronic cluster headache when tested in an adequately powered trial? Why it is still open: The one adequately recruited chronic trial was negative [12] and the second was stopped early and underpowered [20], so a definitive controlled answer is absent.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19