How does medical weight loss (GLP-1) work in the body?
Modern weight loss medicines, known as GLP-1 receptor agonists, work by mimicking the effects of the body's own satiety hormones, which, among other things, delays gastric emptying and sends signals of fullness to the brain. This can help you feel full sooner and make it easier to reduce portion sizes.
The hormone GLP-1 (glucagon-like peptide-1) is naturally released from the gut in connection with meals and plays an important role in the body's appetite regulation and blood sugar control. Treatment also affects the brain's regulation of hunger and fullness. For many patients, these effects can reduce the focus on food and cravings for sweet foods. This biological support can make it easier to maintain the lifestyle changes and calorie deficit required for sustainable weight loss.
Examples of medicines in this treatment group include semaglutide (Wegovy) and tirzepatide (Mounjaro), which have shown good results in clinical studies for the treatment of overweight and obesity.
Who may be eligible for medical weight loss?
Medical treatment for weight loss may be appropriate for people with obesity (BMI over 30), or for people with overweight (BMI over 27) in combination with at least one weight-related health condition, such as type 2 diabetes, high blood pressure or abnormal blood lipid levels. Treatment may be an option for people who need support to achieve and maintain a healthy weight, particularly when previous lifestyle changes have not had sufficient effect.
The assessment is based on current clinical guidelines for the treatment of overweight and obesity. Medication is prescribed following an individual medical assessment by a registered doctor, taking into account factors including medical history, any risk factors, current medication and relevant test results.
The foundation of treatment is long-term, sustainable lifestyle habits around diet and physical activity. Medication is used as medical support to make weight loss easier and reduce the risk of weight regain over time.
What are the most common side effects?
The most common side effects of weight loss medicines are gastrointestinal and primarily include nausea, diarrhoea, constipation, vomiting and, in some cases, stomach discomfort. These symptoms are usually mild to moderate and occur mainly at the start of treatment or when the dose is increased.
The side effects are an expected effect of the medicines' mechanism of action, which delays gastric emptying and affects the body's appetite regulation. For most patients, symptoms gradually decrease as the body becomes accustomed to the treatment.
Many symptoms can be relieved by eating smaller portions, eating slowly, chewing food thoroughly and avoiding fatty or strongly spiced foods. Gradually increasing the dose also helps improve tolerability.
If side effects persist or are severe, it is important to contact the doctor responsible for your treatment for an individual assessment and possible adjustment of the treatment.
Why isn't medication alone enough for long-term results?
Weight loss medication provides the best and most sustainable results when combined with long-term lifestyle changes around diet, physical activity and behaviour. The medicines can help increase feelings of fullness and reduce hunger, but they do not replace the need for sustainable habits over time.
With rapid weight loss, there is a risk of losing muscle mass, particularly if treatment is not combined with sufficient protein intake and regular physical activity, including strength training. Muscle mass is important for the body's function, metabolism and energy expenditure, and a reduction in muscle mass can make long-term weight stability more difficult.
Current medical guidelines therefore recommend integrating medication with personalised support around diet, physical activity and lifestyle habits. The goal is not only weight loss, but also improved metabolic health and a reduced risk of related health conditions such as type 2 diabetes and cardiovascular disease.
Frequently asked questions about medical weight loss
Will I be prescribed medication straight away if I ask for it?
No. Weight loss medicines are only prescribed following an individual medical assessment by a registered doctor. The assessment is based on factors including your health questionnaire, medical history, any risk factors and relevant test results, and is carried out in accordance with current medical guidelines for the treatment of overweight and obesity.
It is always the doctor responsible for your treatment who decides whether medication is medically appropriate for you.
Will I need to take medication for the rest of my life to maintain my weight?
Obesity is a chronic disease in which the body's biological mechanisms can counteract long-term weight loss. After weight loss, hunger regulation, energy expenditure and hormonal signals can change in ways that increase the risk of weight regain, a phenomenon sometimes known as metabolic adaptation.
For some patients, long-term or continuous treatment may therefore be appropriate to maintain results over time. However, the need for continued treatment varies between individuals and is reviewed regularly with the doctor responsible for treatment, based on treatment response, health status and individual treatment goals.
How much weight do people lose on average with treatment?
Clinical studies show that modern weight loss medicines, such as semaglutide and tirzepatide, can contribute to significant weight loss when treatment is combined with lifestyle changes around diet and physical activity. On average, studies have shown weight loss of around 15 to 20 per cent of body weight over approximately 12 to 18 months.
However, results vary between individuals and are influenced by factors such as biological characteristics, adherence to treatment, lifestyle habits and any coexisting health conditions. The goal of treatment is not only weight loss, but also improved metabolic health and a reduced risk of health conditions related to overweight and obesity.
Can I take weight loss medication if I'm pregnant?
No. Weight loss medicines should not be used during pregnancy or breastfeeding, as their safety for the unborn baby and breastfed child has not been sufficiently established. Treatment therefore needs to be stopped well in advance of a planned pregnancy, in consultation with the doctor responsible for treatment.
How long before pregnancy treatment should be paused can vary depending on the medicine used, as different medicines remain active in the body for different lengths of time. It is therefore important to always discuss plans for pregnancy with your healthcare team before starting or stopping treatment.
Does the medication negatively affect my muscle mass?
With any weight loss, there is a risk of losing some muscle mass at the same time, regardless of whether weight loss occurs through lifestyle changes, medication or surgery. There is currently no evidence to suggest that GLP-1-based medicines directly break down muscle mass, but as body weight decreases, some muscle mass may also be lost if treatment is not combined with the right diet and physical activity.
Sufficient protein intake and regular strength training are therefore recommended to preserve muscle mass, strength and energy metabolism during treatment. The goal is primarily to reduce body fat while preserving the body's function and muscle mass as much as possible.
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