Weight-loss injections: effects, eligibility criteria, side effects and limitations

‘Weight-loss injection’ is a colloquial term for prescription medicines used to treat obesity. The term is no longer entirely accurate, as since July 2026, an active ingredient for weight regulation that is taken as a tablet has also been authorised in the EU. There remains a significant gap between the public perception of these medicines as lifestyle products and the medical reality. This article explains how these medicines work, who they are intended for, what side effects may occur and what their limitations are.

Key points at a glance

• This refers to prescription medicines for the treatment of obesity and excess weight accompanied by at least one weight-related comorbidity. They are not intended for voluntary weight loss.
• The active ingredients influence the body’s own appetite and satiety regulation. They are not a substitute for changes to diet and exercise, but are used in conjunction with them.
• Gastrointestinal complaints are among the very common side effects. The prescribing information also includes warnings and situations in which use is not recommended.
• Obesity is considered a chronic condition. In studies, weight increased significantly again on average once treatment had ended.

What is meant medically by the term ‘weight-loss injection’

The term refers to active substances that mimic the body’s own intestinal hormones. They are known as GLP-1 receptor agonists; a newer active substance also acts on the GIP receptor. They are predominantly administered as subcutaneous injections, either once a week or once a day, depending on the active substance. Since July 2026, a tablet for weight management has also been authorised in the EU.

The mimicked hormones are also released naturally after eating and influence satiety and appetite. The prescribing information states that the active substances act on receptors in the brain that regulate appetite and satiety. In addition, the stomach empties more slowly, and blood sugar metabolism is affected. This is why related active substances are also used in the treatment of diabetes.

It is important to make a clear distinction: these are medicinal products authorised for specific indications; they are neither dietary supplements nor cosmetic products. They are supplied only on prescription.

Who is eligible for drug therapy?

The approved indications are for adults with a body mass index (BMI) of 30 or above, as well as for adults with a BMI of 27 or above but less than 30 who also have at least one weight-related comorbidity. The prescribing information lists, amongst other conditions, impaired glucose metabolism including prediabetes and type 2 diabetes, high blood pressure, dyslipidaemia, obstructive sleep apnoea and cardiovascular diseases. One active substance is also authorised for use in adolescents aged 12 and over with obesity, subject to further conditions. The exact criteria vary depending on the medicinal product and are set out in the relevant current product information.

A medical assessment must therefore be carried out prior to treatment. This includes identifying any co-morbidities, the patient’s weight history to date, previous treatment attempts, current medication and determining whether there are any contraindications. Eating habits are also part of this assessment. If an eating disorder is also present, it should be identified and treated in accordance with German guidelines, as it influences the course of treatment.

The German guideline on the treatment of obesity from 2024 does not regard drug therapy as the first step. It makes a non-mandatory recommendation for its use as a supplementary measure alongside a comprehensive approach comprising dietary, exercise and behavioural therapy.

Only a doctor can determine whether such treatment is appropriate in your situation. Your GP’s surgery is usually the best place to start; depending on the situation, you may also need to see a specialist. Find doctors offering weight-loss consultations near you

What has been observed in studies and what this means for you

In large randomised trials, each involving around 2,000 to 2,500 adults without diabetes, the average weight loss over 68 or 72 weeks, depending on the active substance and dose group studied, ranged from around 15 per cent to just over 22 per cent of baseline weight. In the placebo groups, the figure was around 2 per cent. All participants also received a diet and exercise programme.

These figures are averages for a group. Within the studies, the range varied from very marked changes to barely measurable ones. No prognosis can be derived from this for you personally, neither upwards nor downwards. It is therefore advisable to discuss the course of treatment with your GP without making any assumptions about the outcome.

Furthermore, weight is not the only relevant result. Blood pressure, blood sugar levels, mobility, physical resilience and the progression of existing comorbidities are equally important for health.

Side effects, warnings and what requires medical supervision

Very common side effects include nausea, vomiting, diarrhoea and constipation. These occur particularly at the start of treatment and following dose increases, and tend to subside over time in many patients. Common side effects include, amongst others, abdominal pain, headaches, dizziness, fatigue and gallstones. Reactions at the injection site are also described.

The product information lists pancreatitis, amongst other things, as a warning. Persistent severe upper abdominal pain should therefore be assessed by a doctor and not simply ignored. Since 2025, a very rare circulatory disorder affecting the optic nerve has also been included.

When considering when a medicine should not be used, it is worth making a distinction. The only formal contraindication listed in the reviewed product information is hypersensitivity to the active substance or any other ingredients. In addition, there are restrictions on use and warnings, such as the fact that these medicines should not be used during pregnancy and whilst breastfeeding, and that their use should be discussed with a doctor if a woman is planning to become pregnant.

Drug interactions are relevant, particularly because delayed gastric emptying can affect the absorption of other medicines. It has been reported that, for at least one active substance in this class, the efficacy of oral hormonal contraceptives may be impaired. For the same reason, it is important to mention this treatment even before planned procedures involving anaesthesia or deep sedation. Anyone taking other medicines should provide a full list of these.

Another point concerns body composition. With any significant weight loss, lean body mass is lost alongside fat mass. An adequate protein intake and strength training are therefore considered sensible complementary measures, even though there is as yet a lack of robust studies specifically for this class of active substances.

Why treatment must be considered in the longer term

Obesity is medically recognised as a chronic condition. This has implications for expectations regarding treatment. In the extension phase of one of the major studies, weight trends were monitored after both the medication and the lifestyle programme had been discontinued. Within a year, participants regained, on average, around two-thirds of the weight they had previously lost. There was no continuation group in this extension phase. In another study, which compared continued treatment with discontinuation, weight continued to decrease slightly on average amongst those continuing treatment, whereas it increased significantly in the discontinuation group.

It is understood that the heightened satiety signals cease once treatment ends. Direct measurement data on appetite regulation following discontinuation are less reliable than the weight data.

This does not imply that a particular medicine must be taken on a long-term basis. It does, however, mean that the question of what happens afterwards is part of the treatment plan from the outset.

Frequently asked questions

From what BMI are such medicines considered an option?

The approved indications apply from a BMI of 30, and from a BMI of 27 if there is at least one additional weight-related comorbidity. The exact criteria vary depending on the medicinal product. In any case, BMI alone is not the decisive factor, as pre-existing conditions, medication and warnings are also taken into account.

How quickly do you lose weight with this?

There is no general answer to this. The courses of the condition varied considerably across studies, and average values for a group say little about individual cases. A slow increase at the outset is common, meaning that a change only becomes apparent over a period of weeks.

Is the treatment suitable for anyone who wants to lose weight?

No. These are medicines for specific conditions and risk factors, not a means of losing weight at will. If there are indications of disordered eating behaviour, this should be included in the doctor’s assessment, as it influences the course of treatment and may require separate treatment.

What about medicines purchased online?

This is strongly discouraged. When sourcing from places other than pharmacies, the contents, manufacture and labelling cannot be verified. Regulatory authorities have documented cases of counterfeit pre-filled pens; in one instance, these contained insulin instead of the declared active ingredient, which can lead to dangerous episodes of hypoglycaemia. Furthermore, without a medical examination, there is no way of checking for warnings or potential interactions.

Classification

These medicines have transformed the treatment of obesity, but they are neither a substitute for lifestyle changes nor a short-term treatment offering lasting results. When used appropriately, they form part of a long-term treatment plan involving medical supervision, clear objectives and regular monitoring of tolerability.

If you would like to find out which treatment options are suitable for you, a practice with the relevant experience is the right place to turn to. View doctors offering weight-loss consultations by region

Fact-checking as at: 20 August 2026. Key topics checked: Mechanism of action and dosage forms, including EU authorisation of an oral active substance for weight management; authorised indications with BMI and age limits; classification of drug therapy according to the 2024 version of the S3 guideline; results and populations of the authorisation studies, adverse effects with frequency categories, distinction between contraindications and warnings, interactions including anaesthesia and hormonal contraception, course of events following discontinuation, regulatory warnings regarding counterfeit medicines.