Continuous Glucose Monitor (CGM)
A wearable sensor that measures glucose levels in real time throughout the day via a small filament under the skin, historically prescription-only, now increasingly available in over-the-counter wellness versions.
A continuous glucose monitor, commonly abbreviated CGM, is a small wearable sensor, typically worn on the upper arm or abdomen, that measures glucose levels in interstitial fluid via a thin filament inserted just under the skin, reporting readings continuously throughout the day rather than requiring a fingerstick blood test at a single point in time. CGMs have historically been Class II prescription medical devices, developed and validated primarily for managing diabetes, where continuous glucose data materially improves treatment decisions compared to periodic fingerstick testing.
More recently, over-the-counter CGM products have entered the market, marketed to people without diabetes for general metabolic wellness and optimization rather than clinical diabetes management. These OTC products use similar underlying sensor technology but are positioned and regulated differently from prescription CGMs, available without a doctor's prescription but without the same clinical-management backing or treatment-decision validation.
The clinical significance of glucose fluctuations within a normal range in healthy, non-diabetic individuals is still an active area of research; unlike CGM's well-established role in diabetes management, its value for general longevity or metabolic optimization in healthy users has not been established with the same level of evidence.
A person without diabetes wears an over-the-counter CGM for several weeks to see how different meals affect their glucose response, a use case increasingly marketed for metabolic self-optimization, distinct from the prescription CGM a person with diabetes wears as part of an ongoing clinical treatment plan.