Medication treatment of obesity

In addition to lifestyle guidance and surgery, there are medicines that can help with weight loss. Most of these agents act on the hormones and signals that regulate your feelings of hunger and satiety, so that you eat less and feel full for longer. They are always prescribed as a supplement to an adapted diet and more exercise, never as a replacement for these. The results vary greatly from person to person, and the effect only lasts as long as you use the agent. Obesity is a chronic disease, which means that the medication therefore also has to be taken chronically (lifelong). If you stop, the weight usually returns completely. In Belgium these medicines are currently not reimbursed for obesity, so you bear the cost yourself. Whether medication is the right choice for you and whether you are eligible for drug treatment depends on your weight, your health and your goals.

You will first have an intake consultation with one of the doctors. During this consultation you will be informed about obesity and the associated health risks. This is followed by general advice about the various treatments and the necessary examinations. Once all examinations and consultations have been completed, the findings will be discussed in a team meeting to which your general practitioner is also invited. Following this, you will receive a definitive recommendation. Throughout the entire process you can ask questions and take time to reflect on the proposed pathway and the final treatment.

The different medicines and how they work

GLP-1 receptor agonists

This is the most commonly used group. GLP-1 is a gut hormone that is produced after eating. It slows gastric emptying, dampens appetite in the brain and gives a quicker feeling of satiety. Medicines that mimic this hormone thereby ensure that you feel less hungry and experience smaller portions as sufficient.

Semaglutide (Wegovy) — an injection that you administer yourself once a week. The dose is built up gradually to limit side effects. (The variant Ozempic contains the same substance, but in Belgium it is only registered for diabetes, not for weight loss.) Wegovy is what is known as a GLP-1 agonist. It is a hormone that has a stimulating effect (agonist) on the glucagon-like peptide 1 (GLP-1) receptor. It stimulates insulin release, inhibits the secretion of glucagon (sugar reserves in the liver and muscles), slows gastric emptying, reduces hunger and gives a quicker feeling of fullness. The medicine is administered weekly via a subcutaneous injection. Since obesity is a chronic disease, the agent will have to be administered lifelong. Wegovy can give a weight reduction of on average 10-15% of total body weight (depending on dosage), provided you combine this with a healthy diet and sufficient physical exercise.

Liraglutide (Saxenda) — an older GLP-1 injection that you administer every day. Because of the daily injection and the generally somewhat smaller effect, it is chosen less often today than the weekly agents. Saxenda (liraglutide), just like Wegovy or Ozempic, is what is known as a GLP-1 agonist. It is a hormone that has a stimulating effect (agonist) on the glucagon-like peptide 1 (GLP-1) receptor. It stimulates insulin release, inhibits the secretion of glucagon (sugar reserves in the liver and muscles) and slows gastric emptying. Saxenda can give a weight reduction of on average 5-8% of total body weight (depending on dosage), provided you combine this with a healthy diet and sufficient physical exercise.

Rybelsus is a GLP-1 analogue in tablet form. Rybelsus can give a weight reduction of on average 5-8% of total body weight (depending on dosage), provided you combine this with a healthy diet and sufficient physical exercise. Rybelsus, just like Ozempic, is registered in Belgium for the treatment of diabetes and not for weight loss.

Dual GIP/GLP-1 agonist

Tirzepatide (Mounjaro) a weekly injection that acts on two gut hormones at the same time (GIP and GLP-1). In studies this leads on average to the greatest weight loss of the agents discussed. Mounjaro can give a weight reduction of on average 15% and in some patients even 20% of total body weight (depending on dosage), provided you combine this with a healthy diet and sufficient physical exercise. It is, however, one of the most expensive options.

Agent acting on the brain

Naltrexone/bupropion (Mysimba) this medicine comes in the form of a tablet. The active combination acts on the areas in the brain that regulate hunger and reward, thereby reducing appetite and snacking. The effect on weight is generally smaller than with the GLP-1 agents, but for those who do not want injections it can be an alternative. Mysimba can give a weight reduction of on average 5% of total body weight (depending on dosage), provided you combine this with a healthy diet and sufficient physical exercise.

Fat blocker

Orlistat (Xenical) — tablets that block the absorption of fat from food in the gut. It is an older agent with a more limited effect. The side effects (greasy, frequent or hard-to-control stools) are directly related to the amount of fat you eat and make it less pleasant to use for many people.

How do they compare with each other?

Effect on weight. Broadly speaking, the weekly injections show the most results: tirzepatide (Mounjaro) on average the most, followed by semaglutide (Wegovy). Liraglutide (Saxenda), Mysimba and orlistat give on average a smaller weight loss. These are averages from studies — your personal result may be higher or lower.

Form of administration. Wegovy and Mounjaro are weekly injections, Saxenda a daily injection. Mysimba and orlistat are tablets. Those who do not want injections are therefore left with fewer options, often with a somewhat smaller effect.

Side effects. With the GLP-1 and GIP/GLP-1 agents, stomach and intestinal complaints are the most common: nausea, vomiting, diarrhoea or constipation, especially during the build-up phase. They usually decrease as the body gets used to them. Mysimba can cause, among other things, nausea, headache, sleeping problems and an increased heart rate, and is not suitable for certain conditions. Orlistat mainly causes intestinal and stool complaints.

Sustainability. For all agents the same applies: they are treatments for the rest of your life. The weight only stays under control as long as the agent is used in combination with the adapted lifestyle. If you stop, the weight returns.

Advantages and disadvantages at a glance

Advantages

• Non-invasive: no surgery, no anaesthesia, no recovery period.
• Can be useful as a first step or when surgery is not (yet) appropriate.
• Proven and beneficial effect on weight and on certain weight-related conditions.

Disadvantages

• The effect depends on continued use; when stopping, the weight returns.
• Often a long-term to lifelong treatment.
• Side effects, certainly in the initial phase.
• No reimbursement for obesity: you bear the cost entirely yourself.

For obesity, this medication is not reimbursed in Belgium. You pay the full cost yourself, month after month for as long as the treatment lasts. Because it is a long-term treatment, the total cost mounts up considerably. It is therefore wise to draw up a realistic treatment and budget plan together with your doctor in advance.