How GLP-1 weight loss drugs really differ

Novo Nordisk's chief executive, Mike Doustdar, told Reuters on 13 August 2026 that the investor community is wrong to read obesity as "a zero-sum game between two players". He compared the class to insulin, where Novo sells a dozen brands that lower blood sugar in slightly different ways, and said of these drugs: "GLP-1s all reduce weight, but they all do different things"^[1]. He runs one of the two companies selling them. So this piece sets his framing aside and reads the approved labels instead, to work out what actually separates semaglutide from tirzepatide and from the newer pills.

Three different molecules, not three brands of the same one

Start with what is inside the pen or the tablet. Semaglutide is a peptide that activates a single receptor, the GLP-1 receptor. GLP-1 is a gut hormone released after you eat; it prompts insulin release and signals fullness to the brain. Tirzepatide activates two receptors. Its US label describes it as a GIP receptor and GLP-1 receptor agonist^[3], GIP being a second gut hormone that also boosts insulin when blood glucose is already high.

Orforglipron, approved in the US under the brand Foundayo and sold as a film-coated tablet, is not a peptide at all^[4]. It is a small molecule that acts on the same GLP-1 receptor semaglutide does. That is a genuine difference in kind, not a marketing distinction, and it is the reason a pill exists in a class that started as injections only.

How you take it, and the fine print that comes with it

Wegovy, the semaglutide brand licensed for weight management, goes under the skin once a week as an injection. The label escalates the dose from 0.25 mg over sixteen weeks to a maintenance dose of either 1.7 mg or 2.4 mg^[2]. Zepbound, the tirzepatide weight brand, is also weekly and subcutaneous, with maintenance doses of 5, 10 or 15 mg, and 10 or 15 mg when it is used for sleep apnea^[3]. Both are titrated slowly because the side effects arrive early.

The two tablets are where daily routine diverges. Wegovy tablets come with a strict instruction: take one "orally once daily on an empty stomach in the morning with water (up to 4 ounces)", then "wait at least 30 minutes before eating food, drinking beverages or taking other oral medications"^[2]. Foundayo has no such rule. Its label says once daily, with or without food, swallowed whole^[4]. If your mornings are not your own, that gap may matter more to you than a percentage point on the scale.

The labels do not cover the same ground

This is the difference patients hear least about, and it is the one that decides who can be prescribed what. Wegovy injection carries several US indications: reducing the risk of major adverse cardiovascular events in adults with established cardiovascular disease and obesity or overweight; reducing and maintaining weight loss in adults and in patients aged 12 and older with obesity, and in adults with overweight plus at least one weight-related condition; and treating noncirrhotic metabolic dysfunction-associated steatohepatitis, a liver disease^[2]. Wegovy tablets carry the cardiovascular and the weight indications, but for adults only^[2].

Zepbound is licensed to reduce and maintain weight loss, and separately to treat moderate to severe obstructive sleep apnea in adults with obesity^[3]. Foundayo is licensed for weight reduction and maintenance, and so far nothing else^[4]. A reader with sleep apnea and a reader with fatty liver disease are therefore not choosing from the same list, even though every one of these products reduces weight. Indications differ by country too, which we track on the semaglutide regulation section and on the tirzepatide page.

What the one head-to-head trial measured

Only one large trial has put two of these drugs against each other. SURMOUNT-5 randomised 751 adults who had obesity but not type 2 diabetes to the maximum tolerated dose of tirzepatide (10 or 15 mg) or of semaglutide (1.7 or 2.4 mg), injected weekly for 72 weeks^[5]. Mean weight change at week 72 was -20.2% on tirzepatide and -13.7% on semaglutide. Waist circumference fell by 18.4 cm against 13.0 cm^[5]. Gastrointestinal events were the most common problem in both groups, mostly mild to moderate, and clustered during dose escalation^[5].

Read that result for what it is. One comparison, in one population, over 72 weeks, using weight and waist as the endpoints. It tells you nothing about the tablets, nothing about sleep apnea or liver disease, and nothing about which drug a given person will tolerate. Eli Lilly funded it^[5], which is normal for a head-to-head trial and still worth knowing when you read the headline number.

What optionality does not stretch to

A choice only exists once a regulator has approved the thing being chosen. Retatrutide, Eli Lilly's triple agonist, is the compound most often discussed online as the next tier. Its Phase 3 obesity trial, TRIUMPH-1, enrolled 2,335 participants and finished in April 2026^[6]. Finishing a trial is not the same as being approved. DailyMed carries no approved prescribing information for retatrutide; the retatrutide entries it does list are unapproved products registered by a cross-border e-commerce seller^[7]. Our retatrutide page and the regulation hub track that position as it changes.

Some things do not differ at all. All three approved products carry the same boxed warning about thyroid C-cell tumours seen in rodents, with the human risk unknown, and all three are contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN 2^[2][3][4]. Nausea and other gut effects are common across the class, on the semaglutide products and the tirzepatide ones alike. Choosing between agents does not let you choose your way past either of those.

What this means for readers

The choice an individual patient actually faces is narrower than the market picture suggests. It is bounded by which product is licensed for your condition where you live, whether your insurer or health service will pay, and whether a weekly injection or a daily tablet fits the life you have. The head-to-head figure is one input into that, not the answer to it. Availability varies sharply by country, which is why we track semaglutide in the United States and tirzepatide in the United Kingdom on separate pages.

This article is educational and is not medical advice. It does not recommend a dose, a product or a supplier. Which of these medicines suits you, if any of them does, is a decision for a qualified healthcare provider who knows your history, your other medicines and your other conditions.