CGRP inhibitors are a class of medications designed specifically to treat migraines by blocking a protein called calcitonin gene-related peptide, one of the key drivers of migraine pain. First approved in 2018, they represent the first migraine treatments built from the ground up to target the underlying biology of the condition rather than repurposing drugs originally developed for blood pressure, seizures, or depression. There are now eight FDA-approved CGRP inhibitors, split between injectable antibodies used for prevention and oral pills used for both prevention and acute relief.
How CGRP Triggers Migraine Pain
CGRP is a small protein released by nerve fibers that run along blood vessels in and around the brain. During a migraine, nerves in the trigeminovascular system (the network connecting the brain’s outer covering to major facial and head nerves) release large amounts of CGRP. This triggers a cascade: mast cells in the tissue surrounding the brain dump out inflammatory chemicals, blood vessels in the outer brain lining dilate, and nearby pain-sensing nerves become increasingly sensitized. The result is a feedback loop where inflammation makes nerves more reactive, which drives more CGRP release, which fuels more inflammation.
CGRP doesn’t just act at the surface. About half the neurons in the trigeminal ganglion, the main relay station for head and face sensation, contain CGRP. When small pain fibers there release it, neighboring nerve cells and support cells pick up the signal, amplifying the pain message before it even reaches the brain. Inside the brain itself, CGRP receptors sit in areas that process sensory input, contributing to the heightened sensitivity to light, sound, and touch that many people experience during a migraine.
Two Ways These Drugs Block CGRP
CGRP inhibitors use one of two strategies. The first group, monoclonal antibodies, are large lab-engineered proteins. Three of them (fremanezumab, galcanezumab, and eptinezumab) physically bind to the CGRP molecule itself, neutralizing it before it can reach any receptor. The fourth, erenumab, parks itself on the CGRP receptor, blocking the protein from docking. Because antibodies are large molecules, they work primarily outside the brain in the peripheral nervous system and blood vessels.
The second group, called gepants, are small molecules taken as pills. They block the CGRP receptor in a similar way to erenumab but can also cross the blood-brain barrier to some degree, potentially acting on CGRP signaling inside the brain as well. This difference in reach is why some neurologists now combine both classes for patients with difficult-to-treat migraines, reasoning that blocking CGRP in both the peripheral and central nervous systems could produce a stronger effect.
All FDA-Approved CGRP Inhibitors
Seven CGRP inhibitors have been approved by the FDA, with an eighth (zavegepant, brand name Zavzpret) added as a nasal spray for acute treatment. They fall into clear categories based on how you take them and whether they prevent migraines or stop an attack in progress.
For Prevention
- Erenumab (Aimovig): Self-injection once a month
- Fremanezumab (Ajovy): Self-injection once a month or once every three months
- Galcanezumab (Emgality): Self-injection once a month (with a higher loading dose the first time)
- Eptinezumab (Vyepti): IV infusion every three months, administered in a clinic
- Atogepant (Qulipta): Daily oral tablet
For Acute Treatment
- Ubrogepant (Ubrelvy): Oral tablet taken as needed during an attack
- Zavegepant (Zavzpret): Nasal spray taken as needed during an attack
For Both
- Rimegepant (Nurtec ODT): Dissolving oral tablet. Taken as needed for acute attacks or every other day on a schedule for prevention, making it the most versatile option in the class.
What to Expect From Treatment
In clinical trials, the preventive CGRP inhibitors consistently reduced the number of monthly migraine days compared to placebo. Real-world case reports illustrate the range of response: one patient starting erenumab saw monthly migraine days drop from 13 to 7 within the first month. Results vary, and some people respond dramatically while others see modest improvement or none at all. Neurologists typically evaluate response after three months of consistent use before deciding whether to continue, adjust the dose, or switch to a different option.
The injectable antibodies have the advantage of infrequent dosing. Fremanezumab and eptinezumab can be dosed quarterly, meaning just four treatments per year. The oral gepants offer convenience for people who dislike injections, though atogepant requires daily dosing for prevention.
Side Effects
CGRP inhibitors are generally well tolerated compared to older preventive medications like beta-blockers or antidepressants, but they’re not side-effect-free. The most notable issue is constipation. In pre-approval trials, constipation rates looked modest: roughly 2 to 5% for erenumab, 3% for higher-dose fremanezumab, and 7 to 8% for atogepant. But post-marketing surveys tell a different story. Real-world data suggest constipation may affect more than 50% of patients on erenumab, with rates of 20 to 34% depending on the dose in some studies. Galcanezumab and fremanezumab show post-approval constipation rates around 17 to 25%.
This gap between trial data and real-world experience likely reflects longer treatment durations and more sensitive tracking in everyday practice. CGRP plays a direct role in stimulating intestinal movement and fluid secretion, so blocking it slows the gut down. For most people this is manageable with dietary changes or over-the-counter remedies, but for some it becomes a reason to switch medications.
The injectable antibodies can cause reactions at the injection site, including redness, swelling, or pain. Upper respiratory infections and hypersensitivity reactions have also been reported, though serious allergic reactions are rare.
Who Can Get a Prescription
Guidelines adapted from the American Headache Society recommend CGRP inhibitors for people who experience at least four migraine days per month, or fewer if the attacks are severe enough to cause significant disability. Candidates typically need to have tried and failed, or been unable to tolerate, at least one standard preventive treatment. Some insurance plans still require documented failure of two or more older preventive medications before covering CGRP therapies, though these requirements have loosened over time as the drugs have become more established.
Treatment is generally initiated by a neurologist or headache specialist. Response is reassessed after about three months. If migraine days haven’t meaningfully decreased, the typical next step is trying a different CGRP inhibitor or combining a monoclonal antibody with a gepant.
Safety Considerations for Specific Groups
CGRP does more than transmit pain signals. It plays a protective role in the cardiovascular system, helping blood vessels dilate during periods of reduced blood flow. This raises theoretical concerns about blocking it in people with cardiovascular risk factors. CGRP appears to be particularly important in protecting against cardiac events in women, and cardiovascular risk rises significantly after menopause. For postmenopausal women with migraine, the long-term cardiovascular effects of sustained CGRP blockade remain an open question.
Pregnancy is another area of caution. CGRP is involved in blood vessel regulation during pregnancy, and the monoclonal antibodies have long half-lives, meaning they stay in the body for weeks to months after the last dose. Women planning pregnancy are generally advised to stop these medications well in advance. The gepants clear the body much faster, within hours to days, but safety data in pregnant patients is extremely limited for all CGRP inhibitors.