Metabolic medicines.

Start with the clinical question

Type 2 diabetes and obesity can overlap, but they are not interchangeable diagnoses. A diabetes trial may ask whether a treatment lowers HbA1c, reduces hypoglycaemia or changes another risk marker while people continue background medicines. A weight-management trial may ask about body weight, waist circumference, cardiometabolic markers, physical function or maintenance after an initial loss. A cardiovascular-outcomes trial asks a different question again: whether events such as cardiovascular death, myocardial infarction or stroke change over longer follow-up.

The same active substance can have different product names, labels, formulations and authorised uses. The current U.S. Mounjaro label describes tirzepatide for improving glycaemic control in adults and children aged 10 and older with type 2 diabetes, and for reducing major cardiovascular events in adults with type 2 diabetes at high cardiovascular risk. The Zepbound label covers chronic weight management in adults meeting specified BMI and weight-related-condition criteria, and treatment of moderate-to-severe obstructive sleep apnoea in adults with obesity, together with diet and physical activity. Those are product-specific regulatory statements, not a general claim that tirzepatide is suitable for every metabolic condition.11415

Keep jurisdiction and product attached

EMA describes Mounjaro as authorised for type 2 diabetes in adults and children aged 10 years and above under defined conditions, and for weight management in adults with obesity or overweight plus specified weight-related health problems. The EU description and US labels are separate jurisdiction-specific records. Authorisation can change as evidence, labels and safety monitoring change.

The existence of an authorised product does not mean every formulation, compounded preparation, online product or proposed use is authorised. Conversely, a medicine under investigation may have encouraging early findings without being approved for that indication.45

How incretin medicines fit the biology

Some medicines act on receptors for signals released by the gut. GLP-1 receptor activity can affect insulin, glucagon, stomach emptying and appetite. Regulators describe tirzepatide as acting on both GIP and GLP-1 receptors. This helps explain why researchers study it; it does not by itself establish how large or lasting a clinical benefit will be.

A change in a receptor signal may affect appetite or blood sugar. A trial must then measure a defined outcome in a particular group over time. Moving directly from “acts at two receptors” to “prevents disease” skips the evidence in between.5

What diabetes trials can show

SURPASS-2 was a 40-week randomised trial in adults with type 2 diabetes. It compared three tirzepatide doses with semaglutide 1 mg; participants and clinicians knew which treatment was given. Tirzepatide produced larger average reductions in HbA1c and body weight in that study.

The result applies to that population, dose comparison and treatment setting over 40 weeks. Digestive side effects were common in both groups, and the manufacturer funded the trial. It does not rank every diabetes medicine for every person.6

What weight-management trials can show

SURMOUNT-1 studied tirzepatide for 72 weeks in adults with obesity, or overweight and a weight-related complication, who did not have diabetes at the start. It reported substantial average weight reductions at the doses studied.

Those people and that period matter. The results do not directly answer how treatment performs in people with type 2 diabetes, adolescents, people with a different starting weight or people who stop treatment. Studies of keeping weight off can answer a different question from studies of initial weight loss.7

Read benefits and harms together

Across trials and regulator summaries, gastrointestinal effects such as nausea, diarrhoea and vomiting are prominent for incretin-based medicines. Their frequency, intensity, timing and consequences vary by product, dose, titration schedule, comparator and participant characteristics. Read percentages with definitions, follow-up, treatment discontinuations, serious adverse events and missing data. “Common” does not mean harmless, and an adverse event does not by itself prove that the medicine caused it.

The risk context also depends on co-medication and clinical setting. The current Zepbound prescribing information describes gastrointestinal adverse reactions and a hypoglycaemia warning with insulin or insulin secretagogues, alongside other product-specific warnings. In January 2026, FDA said its review found no increased risk of suicidal thoughts or behaviour with GLP-1 receptor agonist medicines and requested removal of that warning from the labels of three named weight-management products, including Zepbound. That communication addresses a specific safety question; it is not a source for every warning or a finding that these products have no other risks. These are not instructions for self-adjustment; they show why a mechanism summary cannot substitute for current prescribing information and professional assessment.283

Do not compare unlike headlines

Two studies can both report “weight loss” but include different people, starting weights, support, missing-data methods and follow-up periods. One may report an average; another may report how many people crossed a threshold. Placing those numbers side by side as if they came from one experiment can overstate what is known.

The same applies to HbA1c, a measure of average blood sugar. An average change, the proportion reaching a target and a clinical outcome such as a heart attack are different results. A marker can be useful without proving every outcome that matters to patients.67910

A current retatrutide evidence snapshot

Three 2026 peer-reviewed reports add phase 3 context to the historical retatrutide studies. TRIUMPH-1 studied obesity without diabetes for 80 weeks; TRIUMPH-2 studied obesity with type 2 diabetes for 80 weeks; TRANSCEND-T2D-1 studied type 2 diabetes inadequately controlled by diet and exercise alone for 40 weeks. They used different populations and primary endpoints, so their placebo-controlled results must not be pooled or treated as a head-to-head ranking. PubMed abstracts report substantial weight changes in TRIUMPH-1 and TRIUMPH-2, and HbA1c and weight reductions in TRANSCEND-T2D-1, alongside gastrointestinal events and dose/population-specific discontinuations. These are Lilly-funded trials and the current appraisal here is abstract-level; full publisher articles and supplements have not been fully appraised here. Retatrutide remains investigational, not an approval or treatment recommendation. Read the historical 2023 study and the profile together for population, comparator and status context.111213

What remains uncertain

Evidence differs across medicines, uses, people and time periods. Trial participants may be healthier or receive closer monitoring than people in routine care. Long-term effects, uncommon harms, staying on treatment, access, cost and what happens after stopping can need further evidence. Manufacturer-funded studies can be rigorous, but funding and author relationships belong in the assessment.72

Five questions for a metabolic-medicine claim

Which medicine and product does the claim concern, and in which country? Who was studied and what other treatment or lifestyle support did they receive? What was measured, against what comparison and for how long? What benefits, harms, treatment stopping, missing data and uncertainty were reported? Is the claim about a biological mechanism, a marker, a patient outcome or an approved use?159103