CGRP
Pain / MigraineAlso known as: Calcitonin Gene-Related Peptide, Alpha-CGRP
Mechanism
A 37-amino acid neuropeptide and the most powerful vasodilator known in the human body. It's the key mediator of migraine headaches — released from trigeminal nerve endings during a migraine attack, causing intense blood vessel dilation and pain. Understanding CGRP revolutionized migraine treatment. Multiple FDA-approved drugs now block CGRP or its receptor (erenumab, fremanezumab, galcanezumab, and the gepant class).
Technical detail
Alpha-CGRP: 37-amino acid neuropeptide encoded by CALCA gene (alternative splicing of calcitonin gene). Released from C-fiber and A-delta trigeminal sensory neurons (cell bodies in trigeminal ganglion). Receptor: heterotrimeric complex of CLR (calcitonin receptor-like receptor) + RAMP1 (receptor activity-modifying protein 1) + RCP (receptor component protein). Activates Gs → cAMP → PKA cascade in vascular smooth muscle → potent vasodilation (10-100x more potent than substance P). Migraine pathophysiology: cortical spreading depression activates trigeminal afferents → CGRP release → meningeal vasodilation, mast cell degranulation, neurogenic inflammation → pain via nociceptive trigeminal pathway. Anti-CGRP therapeutics: monoclonal antibodies targeting CGRP ligand (fremanezumab/Ajovy, galcanezumab/Emgality, eptinezumab/Vyepti) or receptor (erenumab/Aimovig). Small molecule CGRP receptor antagonists (gepants): ubrogepant/Ubrelvy, rimegepant/Nurtec, atogepant/Qulipta.
Effects
## Cardiovascular System [Tier 1 — Extensive Human Data] CGRP is one of the most potent endogenous vasodilators known. It acts on CGRP receptors (CLR/RAMP1 heterodimer) in vascular smooth muscle to cause dose-dependent vasodilation, particularly in cranial, meningeal, and coronary vascular beds. IV infusion causes a 15-25% decrease in mean arterial pressure with compensatory tachycardia. It plays a protective role in hypertension and heart failure — CGRP knockout mice develop hypertension, and CGRP levels are elevated in human heart failure as a compensatory mechanism. ## Nervous System — Migraine Pathophysiology [Tier 1 — Extensive Human Data] CGRP is released from trigeminal sensory neurons during migraine attacks. Serum CGRP levels rise during spontaneous and nitroglycerin-triggered migraine and normalize after successful triptan treatment. IV CGRP infusion triggers migraine-like headache in ~65% of migraineurs but not in healthy controls. CGRP sensitizes trigeminal nociceptors, promotes neurogenic inflammation, and maintains the central sensitization that underlies migraine chronification. It does not cross the blood-brain barrier significantly, so its migraine role is primarily peripheral (dural vasculature, trigeminal ganglion). ## Gastrointestinal System [Tier 2 — Moderate Human Data] CGRP is expressed throughout the enteric nervous system. It inhibits gastric acid secretion, slows gastric motility, and increases mucosal blood flow. Elevated CGRP levels are seen in irritable bowel syndrome (IBS) and functional dyspepsia. It plays a gastroprotective role — CGRP-mediated vasodilation helps maintain mucosal integrity under stress. ## Musculoskeletal System [Tier 2 — Moderate Human Data] CGRP promotes osteoblast differentiation and bone formation. It is released from sensory nerve fibers in periosteum and bone marrow. CGRP receptor signaling enhances fracture healing in animal models. Levels are altered in osteoarthritis joints, where it contributes to both pain signaling and attempted repair responses. ## Immune/Inflammatory System [Tier 2 — Moderate Human Data] CGRP modulates immune responses by suppressing dendritic cell antigen presentation, inhibiting TNF-alpha release from macrophages, and promoting a Th2-skewed cytokine profile. It has a net anti-inflammatory effect in many contexts but contributes to neurogenic inflammation in the trigeminovascular system during migraine.
Practitioner Guide
## The Migraine Revolution: How Anti-CGRP Therapy Changed Everything ### Background for Practitioners Before anti-CGRP drugs, migraine prevention relied on repurposed medications (beta-blockers, antidepressants, anticonvulsants) with modest efficacy and significant side effects. The anti-CGRP class represents the first migraine-specific preventive therapy and has fundamentally changed the treatment landscape. ### The Anti-CGRP Drug Classes **Monoclonal Antibodies (Monthly/Quarterly Injections)** - **Erenumab (Aimovig)** — Targets the CGRP receptor (CLR/RAMP1). The only receptor-targeting antibody. 70mg or 140mg SC monthly. First FDA-approved anti-CGRP (2018). - **Fremanezumab (Ajovy)** — Targets CGRP ligand. 225mg SC monthly or 675mg quarterly. The quarterly option is unique and preferred by patients who dislike frequent injections. - **Galcanezumab (Emgality)** — Targets CGRP ligand. 240mg loading dose then 120mg SC monthly. Also FDA-approved for episodic cluster headache (the only preventive treatment with this indication). - **Eptinezumab (Vyepti)** — Targets CGRP ligand. 100mg or 300mg IV quarterly. The only IV-administered option. Fastest onset of benefit — some patients report improvement within 1-4 days after first infusion. **Receptor vs. Ligand Targeting — Clinical Implications:** Erenumab (receptor blocker) and the ligand-binding antibodies appear comparably effective (~50% of patients achieve ≥50% migraine day reduction). However, some patients who fail one mechanism respond to the other. A practical approach: if a patient fails 2+ months on erenumab, switch to a ligand-targeting antibody, and vice versa. Constipation is more common with erenumab (receptor blockade affects GI CGRP signaling) at ~3-4% incidence. Hypertension has been reported rarely with erenumab. **Small Molecule CGRP Receptor Antagonists (Gepants) — Oral Options** - **Rimegepant (Nurtec ODT)** — 75mg oral disintegrating tablet. FDA-approved for both acute treatment AND prevention (every other day dosing for prevention). This dual indication is unique. - **Ubrogepant (Ubrelvy)** — 50mg or 100mg oral, acute treatment only. Can redose once after 2 hours. - **Atogepant (Qulipta)** — 10mg, 30mg, or 60mg daily oral, prevention only. The first oral CGRP preventive designed purely for daily use. - **Zavegepant (Zavzpret)** — 10mg intranasal spray, acute treatment. Useful for patients with nausea/vomiting who cannot take oral medications. ### When to Recommend Anti-CGRP Therapy - **First-line prevention consideration:** Patients with ≥4 migraine days/month who want to avoid traditional preventives (which have more side effects). - **After traditional preventive failure:** Patients who have tried and failed or cannot tolerate ≥2 traditional preventives (the insurance-required step therapy threshold for most US payers). - **Chronic migraine (≥15 headache days/month):** Anti-CGRP antibodies show strong efficacy here, with ~30% of chronic migraine patients reverting to episodic pattern. - **Medication overuse headache:** Can initiate anti-CGRP therapy while simultaneously withdrawing overused acute medications. Evidence suggests anti-CGRP mAbs facilitate detoxification. ### Practical Dosing Guidance - Set expectations: Most patients see meaningful benefit by month 3. The official guidance is to trial for 3-6 months before declaring failure. - Antibodies have minimal drug-drug interactions (they are catabolized like endogenous proteins, not hepatically metabolized). - Gepants are CYP3A4 substrates — check for interactions with strong CYP3A4 inhibitors (ketoconazole, clarithromycin) and inducers (rifampin, carbamazepine). - No rebound headache risk with gepants (unlike triptans and NSAIDs). - Patients on anti-CGRP prevention can still use triptans or gepants for breakthrough acute attacks. ### Safety Considerations - Theoretical cardiovascular concern: CGRP is a coronary vasodilator and may be cardioprotective. Long-term CGRP blockade safety in patients with established cardiovascular disease is still being studied. Current data (5+ years) show no cardiovascular signal, but most trials excluded patients with significant CVD. - Pregnancy: All anti-CGRP drugs are Category C. Antibodies should be discontinued 5 half-lives before conception (~5 months for most). Gepants have shorter half-lives and can be stopped closer to conception.
Research Summary
## Tier 1 — Strong Clinical Evidence - CGRP is causally involved in migraine pathophysiology (demonstrated by IV provocation studies, serum level measurement during attacks, and the clinical success of anti-CGRP drugs) - Anti-CGRP monoclonal antibodies reduce monthly migraine days by 3.5-6.6 days vs. 1.5-3.0 for placebo across Phase III trials (ARISE, STRIVE, EVOLVE-1/2, REGAIN, HALO, PROMISE-1/2, CONQUER) - Gepants are effective for acute migraine treatment (2-hour pain freedom: 19-21% vs. 11-14% placebo) and prevention (atogepant reduced monthly migraine days by 3.7-4.2 vs. 2.5 placebo) - CGRP is one of the most potent known endogenous vasodilators — well-established cardiovascular physiology ## Tier 2 — Moderate/Emerging Evidence - CGRP may play a role in cluster headache (galcanezumab FDA-approved for episodic cluster headache based on a single positive trial) - Elevated CGRP levels associated with various pain conditions (fibromyalgia, temporomandibular disorder, irritable bowel syndrome) - CGRP promotes bone formation and fracture healing in preclinical models with supportive human tissue data - Long-term cardiovascular safety of chronic CGRP blockade still being evaluated (no signal to date at 5+ years) ## Tier 3 — Preclinical/Theoretical - CGRP may have neuroprotective properties in stroke (preclinical data showing reduced infarct size with CGRP administration) - CGRP-mediated immune modulation could have therapeutic implications beyond headache - Role in wound healing via promotion of angiogenesis and keratinocyte proliferation (animal models)