Why do weight-management medicines mention BMI 27 with a related condition?

You see this wording because it comes from how weight-management medicines are licensed. Approval is generally written around a BMI threshold, with a lower threshold applying when someone also has a weight-related condition such as high blood pressure, type 2 diabetes or obstructive sleep apnoea.

BMI is a screening tool rather than a measure of health. It uses only height and weight, so it does not distinguish muscle from fat and does not account for where fat is carried, which is why it can misclassify very muscular people and why it is used alongside other measures rather than alone.

Where you fall against a threshold is one input into a clinical decision, not the decision itself. If the number puts you just either side of a cut-off, that is a conversation with a clinician about the whole picture rather than a verdict.