Obesity Medications: What they are and how they work

What are obesity medications and how do they work?

Obesity medications are prescription weight loss medicine designed to support weight loss by influencing appetite and satiety regulation and overall energy intake.

Historically, the market for weight loss aids was filled with ineffective supplements. Today, we have entered a new era. Modern prescription weight loss drugs, specifically incretin-based medications, represent a major development in evidence-based obesity management. But how do weight loss injections work?

The most effective treatments available today mimic the effects of naturally occurring hormones in your gut, such as glucagon-like peptide-1 (GLP-1) and glucose-dependent insulinotropic polypeptide (GIP). When you use these medications for obesity, they interact directly with the brain's appetite center. This interaction increases your feeling of fullness and slows down gastric emptying, so food stays in your stomach longer. These medications also influence the brain’s reward pathways, which may reduce intrusive thoughts about food, sometimes referred to as “food noise.”

Who qualifies for a prescription weight loss treatment?

Treatment with approved weight loss medications is strictly regulated to ensure patient safety and clinical efficacy. To be eligible for these treatments, you must meet specific medical criteria based on your Body Mass Index (BMI) and your overall health profile, including the presence of weight-related health problems.

According to European regulatory approvals and clinical practice guidelines, you may qualify if you have:

• BMI ≥ 30: Classified as obesity.

• BMI ≥ 27 with comorbidities: Classified as overweight, accompanied by at least one weight-related health condition, such as type 2 diabetes, high blood pressure, obstructive sleep apnoea, or high cholesterol.

A thorough medical evaluation by a doctor is required before any prescription is issued. When using a digital clinic, an online doctor or healthcare professional should carefully review your medical history, current medications, and blood tests to ensure the treatment is safe for you. Pregnant women, breastfeeding mothers, and individuals with certain medical conditions are not eligible for these medications.

Approved obesity medications

The landscape of medications for obesity has expanded rapidly, offering highly effective weight loss injections and tablets tailored to individual medical needs. Your healthcare professional will help you navigate these options to create a treatment plan that suits your health and lifestyle.

GLP-1 Based Medications

GLP-1–based medications for obesity are GLP-1 receptor agonists that mimic the physiological effects of the endogenous incretin hormone glucagon-like peptide-1 (GLP-1).

• Semaglutide: Branded as Wegovy for chronic weight management (and Ozempic for type 2 diabetes), semaglutide is administered as a once-weekly injection. Semaglutide is also available as a daily oral tablet branded as Rybelsus.

• Liraglutide: Branded as Saxenda, this was the first GLP-1 receptor agonist approved for the treatment of obesity, administered as once-daily injection.

Dual GIP/GLP-1 Medications

The newest generation of treatments targets two incretin hormone receptors simultaneously, enhancing appetite regulation and metabolic control.

• Tirzepatide for obesity: Marketed as Mounjaro (and Zepbound in some markets), tirzepatide is a dual GIP and GLP-1 receptor agonist. By activating both incretin pathways, it produces substantial effects on glycaemic control and body weight. It is currently among the most effective pharmacological treatments available for obesity.

Other Approved Medications

For patients who prefer not to use injectables or who may not tolerate incretin-based therapies, alternative pharmacological mechanisms are available:

• Naltrexone/Bupropion (Mysimba): An oral combination therapy administered daily. It acts centrally by modulating hypothalamic appetite regulation and the mesolimbic reward system, which may reduce food cravings, reward-driven eating, and impulsive intake. It may be particularly useful for individuals whose overeating is linked to emotional or hedonic triggers.

• Orlistat (Xenical): A gastrointestinal lipase inhibitor that acts locally in the digestive tract by reducing the absorption of approximately 30% of dietary fat. Unabsorbed fat is excreted in the stool. Its weight-reducing effect is mediated through reduced caloric absorption rather than appetite suppression.

Results from clinical trials

The increasing use of pharmacological therapy in obesity management is supported by a growing body of high-quality clinical evidence. Randomised controlled trials evaluating modern anti-obesity medications have demonstrated clinically meaningful and sustained weight reduction, representing a substantial advancement in the medical treatment of obesity.

In the extensive STEP clinical trials, patients using 2.4 mg of semaglutide achieved an average weight loss of 15% to 17% of their starting body weight over 68 weeks when combined with lifestyle interventions including a balanced diet and physical activity.

In clinical trials, higher doses of tirzepatide have produced weight reductions approaching 20–22% after 72 weeks in adults with obesity without diabetes, representing one of the most effective pharmacological treatments currently available.  

These clinical trials demonstrate that when combined with structured lifestyle interventions, modern obesity medications can lead to clinically meaningful and sustained weight reduction in a large proportion of patients.

Managing side effects and safety considerations

Like all medications, obesity treatments can cause side effects. Common side effects of GLP-1 based weight loss injections include nausea, constipation, headache, and diarrhea. These gastrointestinal symptoms often improve over time or with dose adjustments to a lower dose.

Gastrointestinal lipase inhibitors may cause oily stools, increased bowel frequency, and fecal urgency, particularly in the setting of higher dietary fat intake. Adherence to a reduced-fat diet significantly decreases the likelihood and severity of these gastrointestinal effects. A healthcare professional should provide guidance on dietary adjustments, side-effect management, and treatment modification if needed.

It is important to inform your healthcare provider about all medications you are taking, including prescription drugs, over-the-counter products, and supplements, as some anti-obesity medications may interact with other therapies. Such interactions can affect drug efficacy or increase the risk of adverse effects.

If you experience symptoms such as severe abdominal pain (which could indicate pancreatitis), symptoms of low blood sugar (particularly in patients using other glucose-lowering medications), or allergic reactions, seek immediate medical attention.

Healthy Eating and Training Alongside Obesity Medication

While obesity medications can help you lose weight, they are most effective when used alongside a reduced calorie diet and healthy lifestyle changes.

A healthy diet rich in whole foods, vegetables, lean proteins, and a low-fat diet helps support weight loss and overall health. Avoiding processed foods, sugary drinks, and high-fat meals is essential. Eating smaller, regular meals can help manage hunger and prevent overeating.

Exercising regularly is also crucial. The World Health Organization recommends at least 150 minutes of moderate-intensity physical activity per week, such as brisk walking, swimming, or cycling. Strength training and balance exercises twice a week support muscle mass and bone health during weight loss.

Support from healthcare professionals, including dietitians and psychologists, can enhance your ability to maintain healthy eating habits and cope with challenges such as emotional eating.  

Long-term weight management and support

Weight loss medications are powerful tools but not quick fixes. Long-term weight management requires ongoing healthy eating, physical activity, and behavioural changes. Many patients regain some weight after stopping medication if lifestyle changes are not maintained.

To support sustained success, patients should receive ongoing care from a specialist weight management service or healthcare team. This includes regular check-ups, nutritional counselling, psychological support, and encouragement to exercise regularly.

Yazen: A comprehensive online weight loss service

While modern medications for obesity are powerful, they are tools, not magic cures. To achieve long-lasting results and preserve your muscle mass during rapid weight loss, weight loss medicine must be combined with comprehensive healthy lifestyle changes and physical activity.

Real-world data from Yazen patients indicate an average weight loss of 16.6% after 18 months of treatment, suggesting that combining obesity medications with structured multidisciplinary support may significantly improve long-term outcomes.

Summary

Obesity medications have revolutionized weight management by providing effective, scientifically backed treatments that work alongside healthy lifestyle changes. These prescription weight loss treatments, including GLP-1 and dual GIP/GLP-1 agonists like semaglutide and tirzepatide, help regulate appetite and satiety to support sustainable weight loss. Eligibility for these medications depends on BMI and weight-related health conditions, and treatment is always guided by healthcare professionals to ensure safety and efficacy.

While side effects are possible, they are generally manageable with proper support. Combining medication with a reduced-calorie diet, regular physical activity, and coaching support offers the best chance for long-term success. Services like Yazen provide a comprehensive digital approach, integrating medication with personalized coaching and medical oversight to help individuals achieve and maintain a healthy weight for improved overall health.

References

Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). The New England Journal of Medicine.
https://www.nejm.org/doi/full/10.1056/NEJMoa2032183

Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). The New England Journal of Medicine.
https://www.nejm.org/doi/full/10.1056/NEJMoa2206038

A Randomized, Controlled Trial of 3.0 mg of Liraglutide in Weight Management. The New England Journal of Medicine.
https://www.nejm.org/doi/full/10.1056/NEJMoa1411892

EMA: Wegovy – EPAR Product Information.
https://www.ema.europa.eu/en/medicines/human/EPAR/wegovy

EMA: Mounjaro – EPAR Product Information.
https://www.ema.europa.eu/en/medicines/human/EPAR/mounjaro

EMA: Saxenda - EPAR Product Information. https://www.ema.europa.eu/en/medicines/human/EPAR/saxenda

EMA: Mysimba - EPAR Product Information. https://www.ema.europa.eu/en/medicines/human/EPAR/mysimba

EMA: Xenical - EPAR Product Information. https://www.ema.europa.eu/en/medicines/human/EPAR/xenical

WHO: WHO Guidelines on Physical Activity and Sedentary Behaviour. https://www.who.int/publications/i/item/9789240015128

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