Calcitonin Gene-Related Peptide (CGRP): Biology, Signaling, Pathophysiological Roles, and Therapeutic Applications

The calcitonin gene-related peptide (CGRP) is a 37-amino acid neuropeptide belonging to the calcitonin family, discovered as a product of alternative splicing of the calcitonin gene. CGRP has emerged as a pleiotropic signaling molecule with widespread distribution in the central and peripheral nervous systems, particularly within primary sensory neurons. This narrative review synthesizes current knowledge on the CGRP system, integrating recent advances in its molecular structure, gene organization, and post-translational processing with high-resolution structural insights into its heterodimeric receptor complex (CLR-RAMP1) obtained through cryo-electron microscopy. We also include long-term safety data on anti-CGRP monoclonal antibodies, emerging cardiovascular risk signals, and novel therapeutic applications in vestibular migraine and pediatric populations. The intracellular signaling cascades activated by CGRP, including the canonical cAMP-PKA pathway, MAP kinase activation, and context-dependent calcium signaling, are discussed in relation to its diverse physiological functions. These encompass vasodilation, nociception modulation, neurogenic inflammation, gastrointestinal motility, bone metabolism, tissue regeneration, and energy homeostasis. The central role of CGRP in migraine pathophysiology is examined to understand the development of targeted therapies. The current pharmacological landscape is reviewed, including the evolution of small-molecule CGRP receptor antagonists (gepants) through three generations and the four approved monoclonal antibodies targeting CGRP or its receptor, with comparative analysis of their efficacy, safety profiles, and clinical positioning. Beyond migraine, emerging and predominantly preclinical roles of the CGRP system are discussed in chronic pain, osteoarthritis, cardiovascular diseases, sepsis, cancer (particularly bone metastases and tumor microenvironment immunomodulation), and neurodegenerative disorders such as Alzheimer's disease. In these areas, the available evidence remains heterogeneous and, in most cases, is not yet sufficient to support clinical translation. Finally, future directions are discussed, including the development of stable CGRP analogs, allosteric modulators, and the potential expansion of therapeutic applications into oncology, intensive care medicine, and neuroprotection.