Obesity is a complex, chronic health condition that can lead to numerous related health issues, including type 2 diabetes, high blood pressure, and certain types of cancer. Managing weight often involves a comprehensive approach, including dietary changes, increased physical activity, and behavioral modifications. For some, medical interventions like prescription medications become part of this broader strategy. This article compares various prescription weight loss medications, discussing their mechanisms, effectiveness, and considerations.
Main Types of Weight Loss Medications
Prescription weight loss medications work through different pathways to help individuals reduce body weight.
One prominent class is GLP-1 receptor agonists, which mimic glucagon-like peptide-1, a natural gut hormone. Medications like semaglutide (Wegovy) and liraglutide (Saxenda) signal the brain to reduce appetite and slow stomach emptying, increasing fullness. A newer medication, tirzepatide (Zepbound), acts as a dual agonist, mimicking both GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) hormones for enhanced appetite suppression.
Another category includes sympathomimetic amines, which primarily affect the central nervous system to suppress appetite. Phentermine is a common example, increasing brain chemicals that reduce hunger signals. These are generally prescribed for shorter durations.
Lipase inhibitors target fat absorption in the digestive system. Orlistat (Xenical) blocks lipase, an enzyme that breaks down dietary fats. This prevents about a third of consumed fat from being absorbed, leading to its excretion.
Combination medications combine two different drugs for a more comprehensive effect. Naltrexone-bupropion (Contrave) acts on brain areas involved in appetite regulation and reward pathways, helping to reduce cravings and control hunger.
Efficacy and Side Effects Compared
The effectiveness and side effect profiles of weight loss medications vary significantly.
GLP-1 Receptor Agonists
Semaglutide has shown substantial weight loss, with trials demonstrating average body weight reductions of 15% to 20% over 68 weeks. Liraglutide typically results in 5% to 10% average weight loss. These are administered via subcutaneous injection, usually once daily or weekly. Common gastrointestinal side effects include nausea, vomiting, diarrhea, and constipation, which often decrease over time.
Sympathomimetic Amines
Phentermine generally leads to 5% to 10% of initial body weight loss over 12 weeks. This oral medication is usually taken once daily. Side effects relate to its stimulant properties and can include increased heart rate, elevated blood pressure, insomnia, and nervousness.
Lipase Inhibitors
Orlistat typically results in 5% to 7% weight loss over a year. Taken orally with each main meal containing fat, its most common side effects are gastrointestinal. These include oily spotting, gas with discharge, fatty or oily stools, and increased bowel movements, often related to dietary fat intake.
Combination Medications
Naltrexone-bupropion typically leads to 5% to 9% weight loss over a year. This oral tablet’s common side effects include nausea, constipation, headache, and dizziness.
Who Qualifies for These Medications?
Prescription weight loss medications are generally for individuals who have struggled to achieve and maintain weight loss through lifestyle interventions alone. Eligibility criteria are primarily based on Body Mass Index (BMI).
Individuals typically qualify with a BMI of 30 kg/m² or higher, classified as obesity. Alternatively, those with a BMI of 27 kg/m² or higher may qualify if they also have at least one weight-related comorbidity. These can include type 2 diabetes, high blood pressure (hypertension), or high cholesterol (dyslipidemia). These medications are for managing a diagnosed medical condition, not cosmetic weight loss.
Before prescribing, a healthcare provider conducts a thorough medical evaluation. This assessment determines if the medication is appropriate and safe. Certain situations may preclude their use, such as pregnancy, a history of eating disorders, or specific heart conditions.
Important Considerations for Treatment
Starting weight loss medication is most effective when integrated with comprehensive lifestyle modifications. Adopting a reduced-calorie diet and increasing physical activity are fundamental components that enhance the medication’s effects and contribute to overall health improvements. These changes create a caloric deficit necessary for weight loss and support long-term weight management.
Weight loss medications are often prescribed for long-term use, as obesity is a chronic condition requiring ongoing management. These medications help individuals maintain weight loss and prevent weight regain. Discontinuing medication often leads to a return of appetite and potential weight regain if lifestyle changes are not sustained.
Ongoing medical supervision is important for safe and effective treatment. Regular follow-up appointments with a healthcare provider allow for monitoring progress, managing side effects, and adjusting dosages as needed. This continuous oversight ensures the treatment plan remains appropriate.
Individuals should approach weight loss with realistic expectations. While medications significantly aid in weight reduction, they are not a quick fix or a substitute for consistent healthy habits. The journey involves commitment to both the medication regimen and lifestyle changes. Costs vary substantially, and insurance coverage differs, so checking with your provider and insurance company regarding potential expenses is advisable.
References
Novo Nordisk. WEGOVY® (semaglutide) injection 2.4 mg. [Accessed July 29, 2025].
Novo Nordisk. SAXENDA® (liraglutide) injection 3 mg. [Accessed July 29, 2025].
Eli Lilly and Company. ZEPBOUND™ (tirzepatide) injection 2.5 mg, 5 mg, 7.5 mg, 10 mg, 12.5 mg, 15 mg. [Accessed July 29, 2025].
Mayo Clinic. Phentermine (Oral Route). [Accessed July 29, 2025].
U.S. National Library of Medicine. Orlistat. [Accessed July 29, 2025].
Currax Pharmaceuticals LLC. CONTRAVE® (naltrexone HCl and bupropion HCl) extended-release tablets. [Accessed July 29, 2025].