Medically reviewed guide · Last updated: 23 June 2026 · Reading time: approx. 12 min

Weight-loss injections compared: Ozempic, Wegovy and Mounjaro explained objectively

Hardly any health topic is currently searched and discussed as much and as controversially as the so-called weight-loss injections. Trade names such as Ozempic, Wegovy and Mounjaro are on everyone's lips, but between hype, headlines and advertising, what these agents actually differentiates often gets lost. This guide places the topic neutrally and objectively: how do the active ingredients semaglutide and tirzepatide differ, how effective are they, which side effects are there, what do they cost and how does it stand with the availability? Important beforehand: these are prescription-only medicines that are only sensible within a medically accompanied therapy. This guide does not replace medical advice and gives no recommendation for a particular preparation. The goal is rather to place the most-searched trend topic seriously and to present the most important facts in such a way that an informed decision together with the medical practice becomes possible.

How weight-loss injections work

All three mentioned preparations belong to the large group of modern incretin mimetics. Incretins are the body's own gut hormones, above all GLP-1 and GIP, that are released after eating and are involved in the regulation of appetite, satiety and blood sugar. The active ingredients imitate these hormones and work via receptors in the gut and in the central nervous system. They increase among other things the glucose-dependent release of insulin and slow the release of the counterpart glucagon, which originally served the treatment of diabetes. In the brain they set the impulse to be full: feelings of hunger are reduced, cravings less frequent, and the preference for very calorie-rich foods decreases. In addition they delay the emptying of the stomach, so that the feeling of satiety lasts longer. Originally GLP-1 receptor agonists were, by the way, developed from a component in the venom of a lizard species, which shows how closely modern medicines and basic research are sometimes connected.

Important is a widespread misconception: the injections do not break down fat directly. They throttle the appetite and change the eating behaviour, so that fewer calories are taken in. That is an important difference to the widespread idea that an injection would, so to speak, dissolve fat. Exactly for this reason experts emphasise that the agents are only lastingly sensible together with a change of diet and more exercise. A weight-loss injection is thus no sure-fire success that alone provides slim results but a medical building block within a more comprehensive change of lifestyle. Without these accompanying measures there is moreover the risk that not only fat but also muscle mass is lost. Originally these active ingredients were developed for the treatment of type 2 diabetes and showed a clear weight reduction as an additional effect, which explains the present use with obesity. From a diabetes medicine, over the years a therapy option in its own right with strong overweight thus arose, which today is intensively researched and developed further.

Approval: why Ozempic is a special case

One point regularly causes confusion: although Ozempic is considered the best-known name, it is in Germany not approved for weight loss. Ozempic contains semaglutide and is exclusively approved for the treatment of type 2 diabetes. If it is nevertheless prescribed for weight reduction, this is a so-called off-label use, that is a use outside the official approval. Such an off-label use too always requires a medical assessment and prescription and is not permissible without these. Wegovy contains the same active ingredient semaglutide but is specifically approved for weight reduction and available in higher dosages. This difference explains why the same active ingredient is sold under two different trade names: one preparation is geared towards the diabetes treatment, the other specifically towards the weight reduction.

Mounjaro with the active ingredient tirzepatide is in Germany approved both for the treatment of type 2 diabetes and for weight reduction with strong overweight. For the use for weight loss, as a rule a body mass index from 30 applies, or from 27 in connection with accompanying illnesses. The body mass index is thereby only a rough indication and does not replace the individual medical assessment of the entire health situation. Which conditions must be met in the individual case and which preparation is suitable the medical practice always assesses. These approval differences are not only formal but also decide whether and under which conditions an agent may be prescribed at all. They are moreover a reason why the same substance under different names can be differently expensive and differently well available.

Effectiveness compared

With the effectiveness, the previous study situation shows a rather clear trend that is, however, to be read carefully and not as a blanket promise. In large approval studies, the average weight reduction under semaglutide was around 15 percent of the starting weight, under tirzepatide around 20 to 21 percent, in each case over about one and a half years and under accompanying lifestyle change. With a starting weight of for example 100 kilograms, this corresponds on average roughly to 15 against around 20 kilograms, whereby the actual values vary strongly. A direct comparison study tended to confirm that with tirzepatide on average more people lost weight and the weight loss turned out larger. The German consumer organisation Stiftung Warentest also rated tirzepatide and semaglutide as the two most suitable active ingredients for weight reduction. In a large direct comparison study, clearly more participants under tirzepatide reached the thresholds of five, ten or fifteen percent weight loss than under semaglutide, while the gastrointestinal side effects were similarly frequent in both groups.

As clear as these figures seem, so important is the placement. The values come largely from separate studies with different study durations and participant groups and are therefore not comparable one to one. Average values moreover say little about the individual case: how much a person actually loses depends on many factors, among them starting weight, accompanying illnesses, tolerability and above all the accompanying change of lifestyle. More strongly effective is therefore not the same as better suited. Which active ingredient is sensible in the concrete case can only be assessed medically and individually. In addition, with both active ingredients many participants in studies discontinued the treatment prematurely, whether because of side effects or costs, which shows that the purely average effectiveness does not depict the whole picture.

Costs and availability

The costs are for many a decisive point and at the same time one of the most frequent reasons for a discontinuation of therapy. The prices depend strongly on the preparation and dosage and lie depending on the source and dose roughly between around 130 and 500 euros per month. Since the treatment runs over many months or even permanently, these amounts add up quickly to several thousand euros a year, which should be realistically planned for in the decision. Mounjaro with tirzepatide tends to be among the more expensive options, Wegovy with semaglutide is often somewhat below it. In addition there are often costs for injection needles as well as for the medical advice and the prescription. Concrete and current prices can best be asked for in the pharmacy, since they can change. In the meantime, with a liraglutide generic there is also a cheaper option than the established preparations, however with an older active ingredient that is injected daily and works on average more weakly.

Particularly important for the cost question is the reimbursement. For pure weight reduction, the statutory health insurers as a rule currently do not cover the costs, because the responsible bodies classify these agents for weight loss as lifestyle preparations. Users therefore mostly have to pay the therapy themselves. If a preparation is, on the other hand, used within a diabetes therapy, the costs can be covered under certain conditions. Private health insurers reimburse differently depending on the tariff and diagnosis. Courts have also confirmed that the statutory insurers do not have to pay the weight-loss injection with pure obesity, so that the costs in most cases are to be borne privately. With the availability, supply shortages occur again and again, in particular with strongly demanded preparations, which can temporarily make the access harder. Anyone who begins a therapy should therefore plan for the fact that not every preparation is deliverable at all times and that a change or a waiting time can be possible, which is likewise best clarified medically and in the pharmacy.

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In sum, weight-loss injections with the active ingredients semaglutide and tirzepatide are effective but complex medicines that can represent a real medical progress in the treatment of obesity. Tirzepatide led in studies on average to a stronger weight reduction, but decisive in the end always remains the individual case. They are not a lifestyle product for fast weight loss but a medically accompanied therapy with side effects, costs and the question of the long-term course after stopping. Precisely this last point is often overlooked: if one stops the injection without having changed the living habits, the weight often returns, which is known as the yo-yo effect. Anyone who understands this and makes the decision together with the medical practice can approach the topic objectively instead of by hype. Important remains in the end that a weight-loss injection is no substitute for a permanent change of diet and exercise but a building block that only in this frame unfolds its full and lasting effect.