Reviews/Anti CGRP Antibodies/Monthly headache days in chronic migraine
Chronic Migraine · CGRP-CMR-01 · v2
This family of injectable antibodies blocks a nerve signalling molecule involved in migraine, and the question is whether they cut the number of headache days each month in people whose migraine is chronic. Several large, well-controlled trials that compared the drug against a dummy injection found fewer headache or migraine days on the drug: fremanezumab lowered headache days per month to 4.6 versus 2.5 on placebo [29], galcanezumab lowered monthly headache days by 4.8 and 4.6 versus 2.7 on placebo [2], and erenumab lowered monthly migraine days by 6.6 versus 3.5 on placebo [34]. A wide range of real-world clinics across different countries saw the same direction of benefit [6][14][35]. The panel noted real caveats: many studies counted migraine days rather than headache days specifically, one trial subgroup showed no clear benefit [12], and the clinic studies had no comparison group. None of these overturned the consistent direction of effect across different antibodies and independent sponsors, which is why the panel treated the direction as settled.
Placebo-controlled phase 3 trials in chronic migraine show the antibodies reduce monthly headache or migraine days: fremanezumab reduced headache days per month 4.6 (monthly dosing) and 4.3 (quarterly) versus 2.5 on placebo [29]; galcanezumab reduced monthly headache days 4.8 and 4.6 versus 2.7 on placebo [2]; erenumab reduced monthly migraine days 6.6 versus 3.5 on placebo in the medication-overuse chronic-migraine subgroup [34]. Independent real-world chronic-migraine cohorts reproduce the reduction, including on the headache-day outcome specifically: erenumab cut monthly headache days 6.3 at month 3 and 6.8 at month 6 [6] and 12.8 in chronic migraine at weeks 45-48 [14], and anti-CGRP antibodies cut monthly headache days 11.9 at 12 months versus 7.6 for onabotulinumtoxinA [35]. The direction is uniform across all four antibodies and multiple sponsors. The contested point: The clearest point of division is the single placebo-controlled chronic-migraine signal that did not reach significance: the Japanese trial's chronic-migraine subgroup difference was -1.57 (95% CI -3.39 to 0.24, p=0.089) [12], against significant placebo-controlled reductions elsewhere [2][29][34]. A secondary tension is outcome fidelity, since much of the corpus reports monthly migraine days rather than the monthly headache days the claim names.
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One reviewer's only job is to attack the finding. The challenges below were weighed before the grade was set.
A large share of the corpus is uncontrolled single-arm real-world cohorts ([6][7][11][13][14][19][20][25][37][38][39]); their large effects are inflated by regression to the mean and open-label expectancy and cannot alone establish a drug effect.
At least one placebo-controlled signal in chronic migraine is NULL: the Japanese RCT [12] CM subgroup difference was -1.57 (95% CI -3.39 to 0.24, p=0.089), not significant — though the subgroup was underpowered.
Where it remains uncertain. One placebo-controlled chronic-migraine subgroup was non-significant (-1.57; 95% CI -3.39 to 0.24; p=0.089) [12], and much of the supporting corpus is uncontrolled single-arm cohorts [6][7][11][13][14][19][20][25][37][38][39].
Aleatory
Responder rates vary widely between and within studies (e.g. 50% headache-day responder rate 34.9% in [11]; ≥50% monthly-migraine-day responders 55.5% for chronic migraine in [8]), so benefit for any single patient is not guaranteed.
Epistemic
The chronic-migraine subgroup in [12] did not reach significance (-1.57; 95% CI -3.39 to 0.24; p=0.089), described as underpowered, leaving genuine uncertainty about effect size in that population.
The load-bearing papers from a corpus of 43, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Independent pivotal RCT (REGAIN) confirming galcanezumab reduces monthly migraine headache days in chronic migraine.
“Both galcanezumab dose groups demonstrated greater overall mean reduction in the number of monthly MHDs compared to placebo (placebo -2.7, galcanezumab 120 mg -4.8, galcanezumab 240 mg -4.6) ( p < 0.001 for each dose compared to placebo).”
Panel auditInternal validity: high · scope of inference: Galcanezumab vs placebo for monthly migraine headache-day reduction in chronic migraine over 3 months.Key limitations: 3-month double-blind window · metric is migraine headache days
Prospective refractory-CM real-world audit reproducing the headache-day reduction.
“The mean reduction in monthly headache days was 6.3 days (P < 0.001) at month 3 and 6.8 days (P < 0.001) at month 6.”
Panel auditInternal validity: low · scope of inference: Erenumab before-after headache-day reduction in refractory chronic migraine with and without medication overuse.Key limitations: no control arm · single centre · refractory selected population
48-week real-world cohort reporting monthly headache day reduction specifically in chronic migraine.
“erenumab treatment reduced MMD by 4.3 ± 5.3 (mean ± SD) in patients with HFEM, and MHD by 12.8 ± 8.9 (mean ± SD) in subjects with CM.”
Panel auditInternal validity: low · scope of inference: Erenumab before-after headache-day reduction over 48 weeks in chronic migraine with >=3 prior failures.Key limitations: no control arm · refractory selected population · p not stated for CM magnitude
Headache-day frequency fell from 21.1 to 11.4 to 8.9 days across administrations, p<0.001.
Panel auditInternal validity: low · scope of inference: Erenumab before-after headache-day reduction in chronic migraine with prior preventive failures.Key limitations: no control arm · small sample · selected refractory population
4 of 43 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.
Convergent, placebo-controlled RCT evidence across three antibodies and sponsors, reinforced by consistent real-world cohorts, firmly establishes that anti-CGRP antibodies reduce monthly headache days in chronic migraine.
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.
Pooled controlled headache-day estimate. No meta-analysis in the corpus aggregates the placebo-controlled chronic-migraine headache-day data, so the class-level effect size and heterogeneity are unquantified. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: Systematic review and meta-analysis restricted to placebo-controlled chronic-migraine RCTs reporting monthly headache days.
Open question: What is the pooled placebo-controlled reduction in monthly headache days specifically in chronic migraine across the antibody class? Why it is still open: The corpus has only individual trials ([2][29][34]) and no meta-analysis combining them on the headache-day outcome.
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 21 Oct 2026 · protocol v0.19