Different receptors, same axis
Sermorelin is an analog of growth-hormone-releasing hormone, corresponding to the active portion of the natural GHRH molecule. It acts at the GHRH receptor.
Ipamorelin is a ghrelin-receptor agonist — a growth-hormone secretagogue acting through a separate pathway, noted in research for its selectivity.
Regulatory standing differs
Sermorelin has a long clinical history and established characterization as a prescription medication.
Ipamorelin has not been through the same approval pathway. That difference matters more than any mechanistic comparison when considering what a provider can appropriately prescribe.
Why they are paired in discussion
Because the two act on separate receptors, research protocols have examined them together — the same reasoning behind pairing CJC-1295 with ipamorelin.
Combination does not mean additive benefit. Whether any of this applies to an individual is a clinical judgment, not an inference from mechanism.