Weight-loss injection: effects, risks & nutrition

Hardly any health topic has changed as radically in such a short time as weight loss. Medications originally developed for people with type 2 diabetes now help millions of people with severe obesity lose weight they had been unable to shed for years. Whether you are currently considering a weight-loss injection, already using one, or simply want to understand what everyone is talking about: this guide gives you the clear, contextualising answers that often fall short in a doctor's appointment.

We are a food supplement company, not a pharmaceutical manufacturer, and we do not sell any injection. That is precisely why we can address the topic in a way that rarely happens: honestly, with sources, and with an eye on what many underestimate. Because the injection takes away your hunger. It does not take away your responsibility for turning weight loss into genuine health.

The key points at a glance

Weight-loss injections are prescription-only medications from the group of GLP-1 receptor agonists. They enhance the feeling of satiety and reduce appetite, so that energy intake drops considerably. For people with obesity they can, prescription-only and prescribed by a doctor, be part of the treatment of severe obesity.

There are three things you should know from the outset:

A relevant part of the weight lost, in registration trials roughly 25 to 40 percent, does not come from fat but from fat-free mass (including muscle).
Because you eat considerably less, the intake of important nutrients also drops. Vitamin D, magnesium, vitamin B12, iron and others can become scarce.
Strength training, sufficient protein and a targeted nutrient supply are not extras, they determine whether you end up healthier or merely lighter.

In the rest of this guide we get concrete: what the injection is, how it works, what it costs, what risks there are, what new developments are coming, and above all how you can really make the process work for you with nutrition, training and nutrient supply.

What weight-loss injections are and which ones currently exist

Behind the term weight-loss injection there are no miracle cures, but active ingredients with clear names. The best known are semaglutide and tirzepatide. They belong to the group of GLP-1 receptor agonists, which mimic a natural gut hormone that signals satiety.

In everyday life you mainly encounter three brand names. Ozempic contains semaglutide and is actually approved for the treatment of type 2 diabetes, but is often used off-label for weight loss. Wegovy contains the same active ingredient, semaglutide, and is the variant explicitly approved for weight reduction in obesity. Both come from the Danish manufacturer Novo Nordisk. Mounjaro, with the active ingredient tirzepatide, comes from the US manufacturer Eli Lilly and acts via two hormone pathways simultaneously, which led to stronger weight reduction in studies.

Wegovy has been approved in the European Union for the treatment of severe obesity since early 2022 and available in Germany since mid-2023. Which preparation is suitable for whom is always decided by your doctor, depending on diagnosis, pre-existing conditions and individual circumstances. You can find a detailed comparison of the three medications in the article Ozempic, Wegovy, Mounjaro: what sets the weight-loss injections apart.

How the weight-loss injection works

GLP-1 receptor agonists mimic the hormone GLP-1, which your gut releases after eating. This signal makes you feel full, slows gastric emptying and dampens appetite. The result is noticeable: you are simply less hungry and eat less of your own accord.

Tirzepatide, the active ingredient in Mounjaro, additionally acts on a second hormone receptor, the GIP receptor. This dual action is considered the reason why weight reduction is on average higher here.

In practice, energy intake under these medications can drop by up to 40 percent. That explains why weight loss is often substantial, and at the same time it explains the central problem of this guide: someone who eats 40 percent less takes in not only fewer calories, but also less protein, fewer vitamins and fewer minerals.

Who the injection is intended for and what it can achieve

Weight-loss injections were developed for people with obesity, or with overweight and additional risk factors, not as a lifestyle shortcut for the last few kilos. For those who have tried unsuccessfully to lose weight for years, the medication can, following a medical decision, be one component of treatment. It is prescription-only and prescribed by a doctor, a point we want to stress once again here. The reduced appetite can create room for more movement, less strain on joints and metabolism, and for a new relationship with one's own body.

The weight reductions achieved in studies are considerable and, depending on the active ingredient and dose, are in the double-digit percentage range. That is a magnitude that was hardly attainable through diet and exercise alone for many people with obesity.

What matters is the attitude behind it. The injection is a medical tool, not a substitute for a healthy lifestyle. It creates the window of time in which change comes more easily, because the constant hunger falls away. What you build in this window, in eating habits, in muscle, in nutrient supply, determines how sustainable the success is.

What the weight-loss injection costs and when insurance pays

In Germany, the statutory health insurers currently do not cover the cost of weight-loss injections for weight reduction alone. Anyone who wants to use the medications purely for weight loss generally needs a private prescription and pays out of pocket.

The monthly costs are significant: Wegovy is up to roughly 276 euros per month, Mounjaro up to roughly 490 euros. The situation is different in the case of diabetes; here a prescription covered by statutory insurance is possible for the corresponding approved preparations.

One point is often overlooked: these therapies are designed for the long term. If you stop the medication, most people regain weight. What you can do to counter this effect is covered in the section on stopping and in detail in the article After the weight-loss injection: maintaining weight and avoiding the yo-yo effect.

Side effects and risks: the honest flip side

No effective medication is without side effects, and honesty is part of a serious assessment. The most common are gastrointestinal complaints: nausea, vomiting, bloating, diarrhoea or constipation. They occur mainly at the start and after a dose increase and often ease over time. A slow, gradual increase in the dose improves tolerability.

Rarer but more serious are possible risks named in the prescribing information and studies: acute pancreatitis, gallbladder problems, strain on the kidneys due to fluid loss, and severe gastrointestinal reactions. Important for context: large analyses do not support a general pancreatitis risk for the entire drug class, and rapid weight loss itself is already a risk factor for certain complaints.

The data on long-term safety is also still limited. The longest controlled studies run for roughly four years for semaglutide and roughly two years for tirzepatide. That is no reason to panic, but a good reason to have the therapy medically supervised and to pay attention to your own body. You can read how to cushion typical gastrointestinal complaints through nutrition in the article Side effects of the weight-loss injection: how nutrition and nutrients make the transition easier.

What is currently developing: tablets and new active ingredients

The field is moving fast, and it is worth knowing the direction. Since early 2026 there has been an oral form of semaglutide, that is, a tablet instead of an injection, which is absorbed in the stomach via a special technology. For many people this lowers the barrier, because the previously necessary injection is no longer needed.

With orforglipron, Eli Lilly is working on an oral active ingredient that is built as a small molecule and is intended to work without strict rules on timing around meals. It is not yet approved; its efficacy and safety have not been conclusively assessed. The manufacturer is, however, seeking approval; whether and when it will come remains to be seen.

Combined approaches go even further, though they too are not yet approved and their efficacy and safety have not been conclusively assessed. Retatrutide acts on three hormone receptors simultaneously; early study data point to a weight reduction in the region of 24 to 26 percent. CagriSema, a combination of cagrilintide and semaglutide, achieved roughly 20 percent weight reduction after 68 weeks in studies. For both: the manufacturers are seeking approval; whether and when it will come remains to be seen. With all this progress, the basic logic stays the same: the more strongly appetite is dampened, the more important it becomes how well you use the food that remains.

The underestimated price: muscle loss

This is the most important blind spot, rarely discussed amid the hype. When you lose weight quickly and substantially, you lose not only fat. A considerable part of the weight lost comes from fat-free mass (including muscle). Across the registration trials (including STEP-1, SURMOUNT-1), summarised in a review (Neeland et al. 2024), this share is around 25 to 40 percent.

In the STEP-1 study on semaglutide, fat-free mass fell by roughly 13 percent, and depending on the analysis it accounted for a large part of the total loss. In the SURMOUNT-1 study on tirzepatide, the share of fat-free mass in the weight loss was around a quarter. The exact figures differ, but the message is clear: muscle loss is real and relevant.

Why this is a problem: muscle is responsible not only for strength and mobility, it is also metabolically active and influences how many calories your body burns at rest. Anyone who loses muscle weakens, over the long term, precisely the structure that helps to maintain weight later. The good news: you can counteract it. Exactly how, you can read in the article Muscle loss under the weight-loss injection: how much you lose and how to counteract it.

What happens to your nutrient supply

When the amount of food drops sharply, the intake of vitamins and minerals almost inevitably drops too. On top of that, food choices often change under the injection and variety decreases. This is exactly what is observed in studies.

Among the nutrients most likely to become scarce with reduced intake are vitamin D, magnesium, potassium, choline, iron, vitamin B12, calcium and thiamin, that is, vitamin B1. This is not a theoretical concern but a practical supply issue that often falls short in the medical follow-up.

Experts therefore recommend paying attention to a nutrient-dense, protein-rich diet, keeping supply under medical review and closing gaps in a targeted way, among other things via a multivitamin. Which nutrients are specifically affected and how you can have your status checked is explored in more depth in the article Nutrient deficiencies under the weight-loss injection: which vitamins and minerals become scarce.

The three pillars that determine your success

If you see the injection for what it is, namely a powerful tool that opens a window of time for you to lose weight, then three pillars determine what you build in this window.

The first pillar is nutrition. When appetite is low, what counts is no longer eating as little as possible, but choosing the little you do eat well: plenty of protein, high nutrient density, a clear meal structure. Perhaps the greatest side benefit of the injection is that it allows a genuine dietary change, best accompanied by consistent tracking of meals, because it teaches you what you really eat. More on this in the articles Nutrition under the weight-loss injection and Tracking meals.

The second pillar is strength training. It is the most effective means against muscle loss, and it is not a topic reserved for pros: two to four sessions per week that engage the entire musculature are enough as a foundation. Sufficient protein and training go together here, protein alone is not enough. You can find the details in Strength training under the weight-loss injection and Protein under the weight-loss injection.

The third pillar is nutrient supply. It is the quiet foundation, without which the first two pillars wobble. Anyone who eats too little must all the more deliberately ensure that the important micronutrients do not fall short.

Where targeted supplementation really makes sense

One thing up front, to be clear: no food supplement replaces the injection, enhances its effect or treats obesity. Supplements belong in a different lane, namely that of basic nutrient supply. That is exactly where they can make sense under a weight-loss injection, because the reduced amount of food leaves gaps.

If you eat considerably less over the long term, a broadly based micronutrient foundation becomes an obvious choice. This is where BASE by Fifty Five comes in, a multivitamin and mineral complex that provides, among other things, vitamin B12 and thiamin, that is, two of the nutrients that frequently become scarce under GLP-1. Vitamin B12, in line with the specifications of the European Food Safety Authority (EFSA), contributes to normal energy-yielding metabolism and to the normal functioning of the nervous system, thiamin to normal energy-yielding metabolism. In everyday terms this means: the base that otherwise comes from food stays covered, even when portions are small.

Two nutrients that BASE deliberately does not contain deserve separate consideration in this context. Vitamin D is among the most common deficiencies of all and contributes to the maintenance of normal muscle function. For that we have RISE by Fifty Five. Magnesium is likewise a typical problem case and contributes to electrolyte balance and to normal muscle function. That is what CALM by Fifty Five is for. Two terms often come up in the weight-loss context: cardiometabolic health refers to the interplay of the cardiovascular system and metabolism, cognitive health to mental performance. As a nutritional building block, PULSE by Fifty Five with the omega-3 fatty acids DHA and EPA can fit here: EPA and DHA contribute to the normal function of the heart from a daily intake of 250 mg, DHA from 250 mg per day additionally to the maintenance of normal brain function.

Which supplement actually makes sense for whom, and what is pure marketing, such as supposed natural weight-loss injections, is assessed in the article Which supplements really make sense under the weight-loss injection.

What happens after stopping

The uncomfortable truth: if you stop the injection without anything having changed in your lifestyle, the old appetite returns, and with it often the weight. That is precisely why the three pillars are not an accompanying measure, but the actual insurance against the yo-yo effect.

Anyone who has preserved muscle during the therapy, learned a sustainable way of eating and kept supply stable stands on a completely different foundation after stopping. How this transition succeeds is covered in the article After the weight-loss injection: maintaining weight and avoiding the yo-yo effect.

FAQ

How does the weight-loss injection work?

Weight-loss injections contain active ingredients such as semaglutide or tirzepatide, which mimic the gut hormone GLP-1. They enhance the feeling of satiety, slow gastric emptying and reduce appetite. As a result, you eat less of your own accord; energy intake can drop by up to 40 percent. Tirzepatide additionally acts on a second hormone receptor.

What is the difference between Ozempic, Wegovy and Mounjaro?

Ozempic and Wegovy both contain the active ingredient semaglutide from Novo Nordisk; Ozempic is approved for diabetes, Wegovy for weight reduction in obesity. Mounjaro from Eli Lilly contains tirzepatide and acts via two hormone pathways, which led to stronger weight loss in studies. Which preparation is suitable is decided by your doctor.

What does the weight-loss injection cost and does health insurance pay?

For weight reduction alone, the statutory health insurers in Germany currently do not pay. Depending on the preparation, up to roughly 276 euros (Wegovy) or up to roughly 490 euros (Mounjaro) per month apply, which you cover yourself. In the case of diabetes, a prescription covered by statutory insurance is possible for the approved preparations.

Can you get the weight-loss injection without diabetes?

Yes, with an appropriate medical indication such as obesity, a weight-loss injection can also be prescribed without diabetes, then generally via a private prescription as a self-payer. The decision is always made by a doctor after individual assessment.

How much muscle mass do you lose with the weight-loss injection?

In registration trials (including STEP-1, SURMOUNT-1), around 25 to 40 percent of the weight lost came from fat-free mass (including muscle). The exact share depends on the active ingredient, dose and individual behaviour. Strength training and sufficient protein can considerably limit muscle loss.

Which nutrients are lacking under the weight-loss injection?

With reduced intake, vitamin D, magnesium, potassium, choline, iron, vitamin B12, calcium and thiamin are most likely to become scarce. The cause is the sharply reduced amount of food and the often lower variety. A nutrient-dense diet and, where appropriate, targeted supplementation help to secure supply.

How much protein should you eat under the weight-loss injection?

To preserve muscle in a calorie deficit, the reference values of the German Nutrition Society (DGE) and EFSA recommend roughly 1.2 to 2.0 g of protein per kilogram of body weight per day, practicably often 1.2 to 1.6 g. Around 20 to 30 g of high-quality protein per meal is sensible; older people tend to need somewhat more. However, many do not even reach the lower guideline value under the therapy.

Do you have to exercise under the weight-loss injection?

Exercise is not a must in a legal sense, but highly relevant from a health perspective. Without strength training, a larger share of the weight is lost from muscle. Two to four strength sessions per week are considered a good foundation for protecting muscle and metabolism.

What happens when you stop the weight-loss injection?

After stopping, appetite returns and many people regain weight. Anyone who has preserved muscle during the therapy, changed their diet and kept supply stable has considerably better chances of maintaining the weight. Stopping should be medically supervised.

All articles on the weight-loss injection and nutrition at a glance

These articles explore individual aspects in detail:

Disclaimer:

This article is for informational purposes only and does not replace medical advice, diagnosis, or treatment by a physician or pharmacist. The information provided here should not be used for self-diagnosis or self-treatment. Food supplements are no substitute for a balanced, varied diet and a healthy lifestyle. For any health questions or complaints, please always consult a doctor you trust. Fifty Five accepts no liability for any inconvenience or harm resulting from the use of the information presented here.

Sources