CGRP and Migraine: The Connection and New Treatments

Calcitonin gene-related peptide, better known as CGRP, is a small signaling molecule released by nerve fibers in and around the brain that plays a central role in triggering and sustaining migraine attacks. Elevated CGRP levels have been measured during migraine episodes for decades, and that discovery eventually led to an entirely new class of medications designed to block either the peptide itself or the receptor it activates. These treatments, which include injectable antibodies and oral pills called gepants, represent the first therapies developed specifically for migraine rather than borrowed from other fields like cardiology or psychiatry.

What CGRP Does During a Migraine

CGRP is produced by sensory nerve fibers that wrap around blood vessels in the membranes covering the brain. When these fibers become activated, they release CGRP, which dilates blood vessels, triggers local inflammation, and transmits pain signals deeper into the brain’s pain-processing centers. Researchers first detected elevated CGRP in the jugular venous blood of people experiencing migraine attacks, providing early evidence that this peptide was more than a bystander.

What made the finding especially compelling was that CGRP levels are not only elevated during attacks. Studies have found that people with migraine carry higher baseline CGRP levels even between episodes, suggesting a kind of chronic sensitization in the system that processes head pain.¹ Infusing CGRP directly into people with migraine can provoke an attack; doing the same in people without a migraine history typically does not produce one. That asymmetry pointed strongly toward CGRP as a driver of the disease, not merely a consequence of pain.

The Receptor CGRP Activates

CGRP does not act alone. It binds to a receptor that is itself unusual: rather than being a single protein, the CGRP receptor is a two-part complex made up of a component called the calcitonin receptor-like receptor (CLR) paired with an accessory protein known as RAMP1.² Neither piece works on its own. CLR needs RAMP1 to fold properly and reach the cell surface, and the shape of the combined receptor determines how tightly CGRP locks in. This two-part design matters because it gave drug developers two distinct strategies: block the CGRP molecule before it reaches the receptor, or block the receptor so CGRP cannot activate it.

Where the Drugs Actually Work

One persistent question was whether anti-CGRP antibodies needed to cross the blood-brain barrier to prevent migraine. Research in rats using fluorescently labeled antibodies tracked where the drugs ended up. The antibodies were found concentrated in the dura (the tough membrane around the brain), dural blood vessels, the trigeminal ganglion, and several other nerve clusters outside the brain. They were not detected inside the brain itself, in areas like the thalamus, hypothalamus, or cortex.³ The implication is that these antibodies prevent migraine by intercepting CGRP signaling in peripheral structures before the pain signal ever reaches the brain. That peripheral site of action also helps explain why the antibodies have relatively few central nervous system side effects compared to older preventive medications.

Monoclonal Antibodies for Prevention

Four monoclonal antibodies targeting the CGRP pathway have reached the market. Erenumab blocks the CGRP receptor itself, while galcanezumab, fremanezumab, and eptinezumab bind to the CGRP molecule directly, soaking it up before it can engage the receptor. All four are given by injection, either monthly or quarterly, with eptinezumab delivered as an intravenous infusion.

The clinical evidence for these antibodies is substantial. In a large controlled trial of erenumab in people averaging about eight migraine days per month, the higher dose reduced monthly migraine days by roughly 3.7, compared to 1.8 days for placebo. Half of patients on the higher dose achieved at least a 50% reduction in monthly migraine days.⁴ A network analysis comparing these antibodies in chronic migraine found that galcanezumab and eptinezumab showed the largest reductions in mean migraine days, while fremanezumab had the strongest results on the measure of how many patients achieved at least a 50% improvement.⁵ Across multiple reviews, these antibodies are generally described as effective and well tolerated for migraine prevention.⁶

Erenumab’s mechanism has been mapped at the molecular level. Its antibody structure features a remarkably long protein loop that wedges deep into the groove between the CLR and RAMP1 subunits of the receptor, physically blocking CGRP from docking.⁷ The ligand-targeting antibodies work differently: galcanezumab, for example, binds circulating CGRP and holds onto it, reducing the free peptide available to trigger the receptor in a dose- and time-dependent fashion.⁸

Gepants for Acute and Preventive Use

Gepants are small-molecule pills that block the CGRP receptor. Unlike the antibodies, they can be taken by mouth and work within hours, making them practical for stopping attacks already in progress. Three gepants are currently available for acute treatment: ubrogepant, rimegepant, and zavegepant (the last taken as a nasal spray). Clinical trials confirm all three outperform placebo for pain freedom and relief of the most bothersome migraine symptom at two hours after dosing.⁹ Their potency is in a similar range to common anti-inflammatory painkillers, but they come with two practical advantages that matter for people with frequent migraine.

First, gepants carry no significant cardiovascular risk, so they can be taken by people who cannot safely use triptans because of heart disease or stroke history. Second, and perhaps more interesting for anyone who has dealt with the problem, animal studies suggest gepants do not cause medication-overuse headache. When mice were given a gepant daily for more than a week, they showed no increase in pain sensitivity. Sumatriptan, by contrast, produced clear worsening of sensitivity over the same period.¹⁰ This is particularly relevant because medication-overuse headache is one of the most common reasons episodic migraine transitions to chronic daily headache.

Two gepants have crossed over into preventive use as well. Atogepant, taken daily, reduced monthly migraine days by about 4.2 at the highest dose in episodic migraine, compared to 2.5 for placebo.¹¹ In chronic migraine, where patients started with many more attack days, atogepant cut monthly migraine days by as much as 7.5, about two and a half more days than placebo.¹² Rimegepant, the same pill used for acute attacks, also showed a modest preventive benefit when taken every other day, reducing monthly migraine days by about 0.8 days more than placebo over three months.¹³ Having a single pill that serves double duty is a practical convenience, though the preventive effect of rimegepant is smaller than what the antibodies or atogepant deliver.

What Happens When a Patient Does Not Respond

Not everyone benefits from CGRP-targeted therapy. The drugs alleviate migraine symptoms in roughly half of patients, leaving a sizable group with little or no improvement.¹⁴ For people who fail one antibody, switching to a different one within the same class can sometimes help. A multi-center study found that patients who did not respond to erenumab (the receptor-blocking antibody) and then switched to a ligand-targeting antibody saw about a third achieve at least a 30% reduction in headache days after three treatment cycles.¹⁵ A controlled study confirmed that switching between antibody classes (receptor-targeting to ligand-targeting, or vice versa) produces better outcomes than going back to standard care alone.¹⁶

There is a biological reason why blocking CGRP might not work for every patient. Migraine attacks can be provoked by mechanisms that bypass the CGRP receptor entirely. A study in humans showed that cilostazol, a drug that raises levels of a second messenger molecule called cAMP inside cells, could trigger migraine attacks even in patients whose CGRP receptors were fully blocked by erenumab.¹⁷ This means the pain pathway can be activated downstream of where anti-CGRP drugs intervene, explaining at least some of the non-responder population.

Side Effects Worth Knowing About

CGRP is not just a pain molecule. It has real jobs elsewhere in the body, and blocking it can create knock-on effects in two main areas: blood pressure and gut function.

On blood pressure, a prospective study of patients starting anti-CGRP antibodies found that both systolic and diastolic blood pressure increased at every follow-up time point. The maximum estimated rise in systolic pressure was about 5 mmHg. A small fraction of patients who started with normal blood pressure eventually needed blood pressure medication after beginning erenumab treatment.¹⁸ A larger study from the Veterans Health Administration found that among patients who already had hypertension, anti-CGRP treatment was associated with a small but steady annual increase in the number of blood pressure medications needed. Among patients without baseline hypertension, though, the rate of developing new hypertension was similar to what was seen with topiramate, a standard older migraine preventive.¹⁹ The overall risk appears modest, but monitoring makes sense, particularly if you already take blood pressure medication.²⁰

Constipation is the other commonly reported issue, and it has a clear mechanistic explanation. CGRP normally helps drive peristalsis, the wave-like muscle contractions that push food through your intestines. It also stimulates fluid secretion into the gut. Blocking CGRP disrupts both of those processes, slowing transit and reducing the water content of stool.²¹ Interestingly, receptor-blocking drugs (like erenumab) may cause more constipation than ligand-targeting antibodies (like galcanezumab or fremanezumab). Animal research suggests this is because blocking the receptor shuts down signaling from a related receptor called AMY1 in addition to the CGRP receptor, while antibodies that grab the free CGRP molecule may leave some residual signaling through AMY1 intact.²²

CGRP’s Protective Role in the Heart

Beyond the gut and blood vessels, CGRP acts as a natural vasodilator and appears to play a protective role in cardiovascular stress. Animal research has demonstrated that CGRP helps protect the heart during events like ischemia (reduced blood flow), heart failure, and high blood pressure.²³ This has naturally raised the question of whether long-term CGRP blockade could increase cardiovascular risk. So far, clinical trials have not shown a clear signal of heart attacks or strokes in people taking anti-CGRP treatments, and the drugs have been used widely enough to give some reassurance. Still, CGRP’s vasodilating function in healthy physiology is well established,²⁴ and long-term cardiovascular outcomes over decades of use remain an open question that ongoing pharmacovigilance should eventually help answer.

Pregnancy, Breastfeeding, and Limited Data

Migraine disproportionately affects women of childbearing age, so the safety of these drugs during pregnancy and breastfeeding is a practical concern. So far, direct clinical trial data in pregnant women is essentially absent, because trials excluded them. A disproportionality analysis of global safety reports found that anti-CGRP therapies did not show higher rates of adverse pregnancy or fetal outcomes compared to triptans, which have a longer track record of use during pregnancy.²⁵ That is somewhat reassuring but far from definitive, given the limited exposure data.

For breastfeeding, one early study of atogepant in healthy lactating women found that the drug appeared in breast milk at levels roughly 93% lower than in plasma. The estimated relative infant dose was well under 1% of the mother’s dose, and no safety signals emerged in the small group studied.²⁶ These are encouraging numbers, but the study was small, and current prescribing guidance generally recommends caution.

Beyond Migraine: Cluster Headache

CGRP is not unique to migraine. It is also released during cluster headache attacks, which are shorter but often described as even more excruciating. Galcanezumab was tested in episodic cluster headache and showed a significant reduction in weekly attack frequency compared to placebo, with about 71% of treated patients achieving at least a 50% reduction at three weeks.²⁷ Real-world use has supported those findings.²⁸ However, in chronic cluster headache, where attacks persist for months or years without remission, a phase 3 trial of galcanezumab failed to meet its primary endpoint.²⁹ The disconnect between episodic and chronic cluster headache results suggests that CGRP plays a different or less dominant role once the condition becomes continuous.

Salivary CGRP as a Potential Biomarker

One appealing idea is to use CGRP levels to diagnose migraine or predict who will respond to treatment. Saliva is the easiest fluid to test, and early research has found that people with episodic migraine have higher salivary CGRP levels between attacks than healthy controls.³⁰ Even more interesting, one study found that saliva CGRP levels rose during the premonitory and headache phases of an attack, and patients who responded well to a triptan saw their levels drop back toward baseline. Non-responders showed no such drop.³¹ If this finding holds up in larger studies, a simple saliva test could eventually help clinicians identify which patients are likely to benefit from CGRP-targeted drugs before prescribing them, rather than relying on the current trial-and-error approach.

Cost, Insurance, and Sticking With Treatment

Anti-CGRP antibodies are expensive compared to older generic migraine preventives like topiramate or propranolol. In many health care systems, insurers require patients to try and fail cheaper options before covering a CGRP-targeted therapy. A European cost-benefit analysis of working-age migraine patients found that when you factor in reduced emergency visits, fewer specialist appointments, and fewer lost workdays, anti-CGRP antibodies generated net savings of roughly 640 euros per patient per year despite the higher drug cost.³² In the United States, a claims-database analysis of chronic migraine patients found that total healthcare costs were essentially the same whether a patient received anti-CGRP antibodies or botulinum toxin injections.³³

The financial burden still matters for persistence. A real-world Korean study of patients treated with anti-CGRP antibodies found that those with national insurance coverage had notably higher rates of staying on treatment at six and twelve months compared to those paying out of pocket, even though the overall sample was small.³⁴ A drug that works well does not help much if a patient cannot afford to keep taking it, and that tension between clinical efficacy and financial access is one of the defining challenges for this class of treatment going forward.