CGRP: From Calcitonin Gene to Migraine Target

Parathyroid Hormone

40 years

From its discovery as an alternative splice product of the calcitonin gene in the 1980s to FDA-approved migraine therapies, CGRP's journey spans four decades of neuroscience.

Edvinsson et al., Physiological Reviews, 2019

Edvinsson et al., Physiological Reviews, 2019

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Calcitonin gene-related peptide (CGRP) is a 37-amino-acid neuropeptide that exists in two forms: alpha-CGRP (expressed primarily in sensory neurons) and beta-CGRP (expressed mainly in the enteric nervous system). Both are produced through alternative splicing of the calcitonin gene, a molecular accident that turned out to be one of the most consequential findings in headache medicine. The discovery that CGRP is released during migraine attacks and that blocking it prevents them led to the first class of drugs designed specifically for migraine prevention. For context on CGRP's parent molecule and gene family, see our article on calcitonin, and for the broader story of how this peptide transformed headache treatment, see CGRP and migraines.

The path from gene discovery to FDA-approved therapy took roughly 35 years. This article traces that journey: how CGRP was discovered, why it matters for migraine, how the drugs that target it work, and what the clinical evidence shows about their effectiveness.

Discovery: An Alternative Splice Product

In 1982, researchers made an unexpected finding: the gene encoding calcitonin (a peptide hormone involved in calcium metabolism) also produced a completely different peptide through alternative RNA splicing. In the thyroid's C-cells, the gene produces calcitonin. In sensory neurons, the same gene produces CGRP. Same DNA, different protein, different tissue, different function.^[1]

This was one of the earliest demonstrations that alternative splicing could generate functionally distinct proteins from a single gene, a principle now recognized as a fundamental mechanism of proteomic diversity. CGRP turned out to be the most potent vasodilator peptide known, with activity at picomolar concentrations. It is expressed throughout the peripheral and central nervous system, with particularly dense expression in trigeminal sensory neurons, the neurons that innervate the head, face, and meninges. This anatomical distribution immediately suggested a role in head pain, but proving it took another two decades of painstaking work connecting the peptide to the clinical phenomenon of migraine.

The connection to the parathyroid hormone family reflects shared evolutionary origins. CGRP, calcitonin, amylin, and adrenomedullin form a peptide superfamily that signals through related receptors, with overlapping but distinct physiological roles.

Why CGRP Matters for Migraine

The link between CGRP and migraine was established through three converging lines of evidence.

Elevated CGRP during attacks. Blood samples taken from the external jugular vein during migraine attacks showed elevated CGRP levels compared to headache-free periods. This was the first direct evidence that CGRP is released during migraine episodes, not just present in the relevant tissues. Subsequent studies confirmed that CGRP levels normalize after successful triptan treatment, further linking the peptide to the active headache state.^[2]

CGRP infusion triggers migraine. Intravenous infusion of CGRP in migraine patients reliably triggered migraine-like attacks, while the same infusion in non-migraine subjects produced only a mild headache or no headache. This demonstrated that migraine patients have an abnormal sensitivity to CGRP, suggesting the peptide does not merely correlate with attacks but participates in causing them.

CGRP blockade prevents migraine. The definitive evidence came when blocking CGRP (first with small-molecule antagonists, then with monoclonal antibodies) prevented migraine attacks in clinical trials. This completed the causal chain: CGRP rises during attacks, exogenous CGRP triggers attacks, and blocking CGRP prevents attacks.^[3]

The mechanism involves the trigeminovascular system. Trigeminal nerve activation (triggered by cortical spreading depression, stress, hormonal changes, or other migraine triggers) releases CGRP from perivascular nerve endings around meningeal blood vessels. CGRP then binds its receptor on vascular smooth muscle cells, causing vasodilation. It also activates satellite glial cells and mast cells, promoting neurogenic inflammation. The combined effect is pain signal amplification through both peripheral and central sensitization.^[4]

The Monoclonal Antibody Revolution

The development of anti-CGRP monoclonal antibodies represented a paradigm shift in migraine prevention. Prior preventive treatments (beta-blockers, anticonvulsants, antidepressants, botox) were all repurposed from other indications. The anti-CGRP mAbs were the first drugs designed from the ground up to prevent migraine.

Four monoclonal antibodies targeting the CGRP pathway are now FDA-approved:^[5]

Erenumab (Aimovig), approved 2018, targets the CGRP receptor itself rather than the peptide. Administered monthly by subcutaneous injection. It was the first anti-CGRP therapy to reach the market.

Fremanezumab (Ajovy), approved 2018, targets the CGRP peptide directly. Available as monthly or quarterly subcutaneous injection.

Galcanezumab (Emgality), approved 2018, targets the CGRP peptide. Monthly subcutaneous injection. Also approved for episodic cluster headache.

Eptinezumab (Vyepti), approved 2020, targets the CGRP peptide. Administered quarterly by intravenous infusion. Fastest onset of action among the mAbs due to IV delivery.

Clinical trials across all four antibodies showed consistent results: approximately 50% reduction in monthly migraine days compared to baseline, with about 25-30% of patients achieving a 75% or greater reduction. Response rates were significantly better than placebo across episodic and chronic migraine populations.^[6]

Gepants: Small-Molecule CGRP Antagonists

Alongside the monoclonal antibodies, a separate class of oral CGRP receptor antagonists called gepants was developed. First-generation gepants (telcagepant, olcegepant) showed efficacy but were abandoned due to hepatotoxicity concerns. Second-generation gepants solved this problem.

Ubrogepant (Ubrelvy), approved 2019 for acute migraine treatment. Oral tablet taken at migraine onset.

Rimegepant (Nurtec ODT), approved 2020 for both acute treatment and prevention. The first oral CGRP antagonist approved for preventive use (every other day dosing).

Atogepant (Qulipta), approved 2021 for migraine prevention. Daily oral tablet.

Gepants have a different pharmacological profile than antibodies. They are small molecules with short half-lives (hours vs. weeks for mAbs), which means their effects are reversible within a day. This is both an advantage (rapidly reversible if side effects occur) and a limitation (require more frequent dosing for prevention).

The existence of both mAbs and gepants gives clinicians a range of options: injectable but infrequent antibodies for patients who prefer less frequent dosing, or daily/every-other-day oral gepants for those who prefer pills over injections.^[7]

Real-World Effectiveness

Clinical trial populations are selected for study: they exclude patients with many comorbidities, those who have failed numerous prior treatments, and those taking certain concomitant medications. This means the roughly 50% migraine day reduction seen in pivotal trials may not reflect what happens in a broader clinical population that includes patients with medication overuse, psychiatric comorbidities, and treatment-refractory disease. Real-world effectiveness data provides a more complete and clinically relevant picture of how anti-CGRP therapies perform in routine practice.

A 2022 study of anti-CGRP monoclonal antibodies in real-world settings confirmed that the treatment effects observed in clinical trials translated to routine clinical care. Patients showed sustained reductions in monthly migraine days, acute medication use, and disability scores, with benefits persisting over extended treatment periods.^[8]

More recent 2026 real-world data has further validated these findings, with long-term follow-up showing that responders typically maintain their improvement over years of continuous treatment. Some patients who did not respond to one anti-CGRP antibody responded to switching to a different one, suggesting that the three CGRP-targeting and one receptor-targeting antibodies are not fully interchangeable.^[9]

A 2023 review of advances in anti-CGRP monoclonal antibody therapy found that the drugs also improved quality-of-life measures beyond headache frequency, including reduced anxiety, improved work productivity, and decreased emergency department visits for migraine.^[10]

CGRP Beyond Migraine

CGRP is not exclusively a pain molecule. It has physiological roles in cardiovascular protection (vasodilation during ischemia), wound healing (promoting angiogenesis), immune modulation, and gastrointestinal function. These broader functions raise theoretical questions about long-term CGRP blockade.

In the cardiovascular system, CGRP acts as a protective vasodilator during myocardial ischemia. Animal models suggest CGRP release helps limit infarct size during heart attacks. Whether chronic CGRP blockade in migraine patients increases cardiovascular risk is an active question. Clinical trial data and post-marketing surveillance through 2026 have not identified a cardiovascular safety signal, but the typical migraine patient population (younger, predominantly female) may not be the group where such a signal would emerge.

CGRP also plays roles in bone metabolism (linking it back to its calcitonin gene family origins), insulin secretion, and mucosal protection in the gut. These functions create a theoretical basis for monitoring long-term safety that extends beyond the 1-2 year durations of most clinical trials. The connection to PTH-related peptide through the shared calcitonin gene superfamily underscores the complexity of blocking one member of a peptide family with pleiotropic functions.

Modulating Rather Than Blocking

A 2026 review explored approaches to modulating CGRP signaling rather than blocking it completely, recognizing that complete pathway suppression may not be ideal given CGRP's protective physiological roles.^[7] Strategies under investigation include partial CGRP receptor antagonism, targeting specific CGRP receptor splice variants expressed preferentially in pain pathways, and combination approaches that reduce the dose of anti-CGRP therapy needed for migraine prevention.

The field has also explored whether CGRP-targeting therapies might work for conditions beyond migraine. Cluster headache (galcanezumab has approval for episodic cluster headache), post-traumatic headache, and medication-overuse headache have all been studied with anti-CGRP approaches, with varying degrees of success. The therapeutic scope of CGRP modulation may extend further: recent preclinical work has explored CGRP's role in visceral pain, inflammatory bowel disease, and even wound healing. Whether anti-CGRP therapies will eventually be used for non-headache indications depends on whether the risk-benefit profile favors CGRP blockade in populations without the clear upside seen in migraine patients.

The speed of clinical adoption for anti-CGRP therapies has been remarkable by pharmaceutical standards. Within 5 years of the first FDA approval, these drugs became first-line options in migraine prevention guidelines. This adoption reflects both the strength of the mechanistic evidence and the unmet need: prior to anti-CGRP drugs, migraine prevention relied entirely on repurposed medications with significant side effects and modest efficacy. The CGRP story represents a model for how understanding a single peptide's pathophysiology can transform treatment for a common disease.

The Bottom Line

CGRP's journey from a molecular curiosity (an alternative splice product of the calcitonin gene) to the foundation of the first migraine-specific drug class represents one of the clearest examples of bench-to-bedside translation in peptide science. The evidence chain is unusually complete: CGRP rises during attacks, triggers attacks when infused, and prevents attacks when blocked. Eight FDA-approved drugs now target this pathway, with real-world data confirming sustained effectiveness over years of treatment. The remaining questions center on long-term safety of chronic CGRP blockade, optimal patient selection, and whether more nuanced modulation of CGRP signaling can preserve migraine prevention while maintaining the peptide's protective cardiovascular and metabolic functions.

Frequently Asked Questions

What does CGRP stand for and what does it do?

CGRP stands for calcitonin gene-related peptide. It is a 37-amino-acid neuropeptide produced by alternative splicing of the calcitonin gene, primarily expressed in sensory neurons. During migraine attacks, it is released from trigeminal nerve endings, causing vasodilation, neurogenic inflammation, and pain signal amplification. It also has protective roles in cardiovascular function and wound healing.

How do anti-CGRP drugs prevent migraines?

Anti-CGRP drugs work by either binding the CGRP peptide directly (fremanezumab, galcanezumab, eptinezumab) or blocking the CGRP receptor (erenumab), preventing CGRP from activating the pain and inflammation pathways involved in migraine. Clinical trials show these drugs reduce monthly migraine days by approximately 50%, with some patients achieving 75% or greater reduction.

What is the difference between CGRP antibodies and gepants?

CGRP antibodies (erenumab, fremanezumab, galcanezumab, eptinezumab) are large proteins given by injection or infusion every 1-3 months with effects lasting weeks. Gepants (ubrogepant, rimegepant, atogepant) are small molecules taken as oral tablets with effects lasting hours. Antibodies are used for prevention only; some gepants are approved for both acute treatment and prevention.

How effective are CGRP migraine drugs in the real world?

Real-world studies from 2022-2026 confirm that anti-CGRP therapies work in routine clinical practice, not just controlled trials. Patients show sustained reductions in migraine frequency, acute medication use, and disability scores over years of treatment. Some patients who fail one anti-CGRP drug respond to switching to another, suggesting the drugs are not fully interchangeable.

Are there long-term safety concerns with blocking CGRP?

CGRP has protective roles in cardiovascular function, wound healing, and gut mucosal protection. Chronic blockade theoretically could affect these functions. Through 2026, clinical trial data and post-marketing surveillance have not identified significant safety signals, but most study populations are younger and predominantly female, which may not be where cardiovascular risks would be most apparent. Long-term monitoring continues.

Is CGRP related to calcitonin?

Yes. CGRP is produced from the same gene as calcitonin through alternative RNA splicing. In thyroid C-cells, the gene produces calcitonin (a calcium-regulating hormone). In sensory neurons, the same gene produces CGRP (a vasodilator and pain-related peptide). They are part of a peptide superfamily that also includes amylin and adrenomedullin.