Blood tests for the GLP-1 era.

GLP-1 medications, Ozempic, Wegovy, Mounjaro and their relatives, have changed weight loss in the UK faster than any drug class in memory, with well over a million people now estimated to be using them. What has not kept pace is monitoring. Many people start a powerful metabolic medication, often bought privately online, with no baseline bloods at all, which means no way of knowing what the drug is doing to the systems it touches.

Blood testing earns its place at three moments. Before starting, a baseline of liver, kidney, thyroid and metabolic markers records where you began and flags anything that needs a doctor's input first. During treatment, markers such as HbA1c and fasting insulin show whether the metabolic picture is genuinely improving, while nutritional markers matter because eating much less can quietly mean absorbing much less: B12, iron, vitamin D and folate all deserve attention when appetite drops sharply. And because rapid weight loss takes muscle as well as fat, the wider picture, including protein intake and strength work, is worth tracking honestly.

The guides below cover each medication and each marker in plain English: what it measures, the UK reference ranges, what changes on a GLP-1 and what should prompt a conversation with your prescriber. They are education, not a substitute for the monitoring your prescriber provides, and any new or worsening symptom on these medications belongs with a clinician promptly.

At-home testing works with a finger-prick kit posted to a UKAS-accredited UK laboratory, with results reviewed by a qualified clinician, usually within days. For GLP-1 users it is a practical way to hold a baseline before the first dose and to watch the trend as the months pass, so decisions about dose and duration rest on numbers rather than guesswork.