Mounjaro (tirzepatide) is the most effective weight-loss medication available, causing 14.9% more weight loss than lifestyle changes alone after one year. However, a comprehensive analysis of 262 randomized controlled trials reveals a significant trade-off: Mounjaro also causes the largest loss of lean muscle mass, which could make it harder to maintain weight loss after stopping the medication.

Which Weight-Loss Drugs Work Best?

Researchers analyzed how much weight people lost on different medications compared to healthy eating and exercise alone. The findings show a clear ranking of effectiveness, with all top performers belonging to a class of drugs called GLP-1 agonists. These medications work by mimicking hormones in the body to lower appetite, slow digestion, and increase feelings of fullness, helping people eat less naturally.

• Mounjaro (tirzepatide) injection: 14.9% more weight loss than lifestyle alone; available on the UK National Health Service (NHS) if you meet certain criteria
• CagriSema (cagrilintide-semaglutide) injection: 14.8% more weight loss; not yet approved in the UK
• Wegovy (semaglutide) pill: 10.9% more weight loss; available only by private prescription in the UK
• Orforglipron pill: 9.9% more weight loss; not yet approved
• Wegovy (semaglutide) injection: 9.8% more weight loss; available on the NHS if you meet certain criteria

Some older medications, including Saxenda (liraglutide), orlistat, and Mysimba (naltrexone-bupropion), were not found to be more effective than lifestyle changes alone.

Why Muscle Loss Matters More Than You Might Think?

While Mounjaro delivers the strongest weight-loss results, the study uncovered a concerning pattern: the most effective drugs also cause the most muscle loss. Mounjaro led to an 8.3% loss of lean mass, such as muscle tissue, compared to lifestyle changes alone. The Wegovy injection caused a 5.8% loss of lean mass, while the Wegovy pill had a smaller effect at 3.3%.

This matters because losing muscle during rapid weight loss can slow your metabolism, making it harder to keep the weight off once you stop taking the medication. Muscle tissue burns more calories at rest than fat tissue, so preserving it is crucial for long-term weight management success.

How to Protect Your Muscles While Taking Weight-Loss Medications

• Eat adequate protein: Consuming more protein helps preserve muscle mass during weight loss and supports your body's ability to maintain lean tissue
• Do regular strength exercises: Resistance training and weight-bearing activities help prevent muscle loss and maintain metabolic rate
• Combine medication with healthy behaviors: Weight-loss drugs work best alongside healthy eating, regular physical activity, and other sustainable lifestyle changes

The Heart Health Trade-Off: Which Drug Protects Your Cardiovascular System?

Interestingly, the most effective weight-loss drug is not the best for heart health. While Mounjaro ranked first for weight loss, the Wegovy injection proved superior at reducing cardiovascular risk. People taking weekly Wegovy injections were 28% less likely to have a heart attack and 19% less likely to die from any cause after 57 weeks, compared to those making lifestyle changes alone.

Both Wegovy and Mounjaro lowered the risk of developing heart failure by 57% and 51% respectively after one year. Mounjaro also reduced hospitalizations for heart failure by 53%. However, neither medication decreased the risk of stroke, and neither significantly improved participants' overall quality of life scores based on self-reported health and wellbeing.

What About Side Effects and Treatment Burden?

The analysis revealed that more effective weight-loss medicines tend to come with greater side effects and higher discontinuation rates. CagriSema caused the most gallbladder-related disorders, while Mysimba led to the most digestive problems and fatigue. The researchers concluded that "larger benefits are generally accompanied by greater harms, treatment burden, and discontinuation".

This means choosing a weight-loss medication involves balancing effectiveness against tolerability. A drug that causes fewer side effects might be worth considering even if it produces slightly less weight loss, especially if it helps you stay on treatment long-term.

Why the Study's Limitations Matter for Your Decision?

The analysis combined data from nearly 100,000 adults with an average age of 49 and body mass index (BMI) of 34.7, roughly equivalent to 245 pounds for someone 5'10". However, most trials were relatively short, averaging around 26 weeks, with only a few lasting longer than two years. This limited timeframe makes it difficult to assess long-term effectiveness, especially for measuring cardiovascular disease risk, which typically develops over decades.

Newer drugs like the Wegovy pill and CagriSema have fewer long-term studies available. For example, researchers found only two trials on orforglipron compared to 31 trials on the Wegovy injection, meaning evidence for newer medications is less certain.

"For some of the medicines included in the analysis, the evidence is still emerging with trials in progress, so it is too early to make strong conclusions of their relative effects," said Dr. Sonya Babu-Narayan, Clinical Director and cardiologist at the British Heart Foundation.

Dr. Sonya Babu-Narayan, Clinical Director and Cardiologist, British Heart Foundation

Dr. Babu-Narayan added that the findings reinforce an important message: "GLP-1 medicines, prescribed by a doctor, are an important option for some people and that they work best alongside healthy eating, regular physical activity, including strength exercises, and other healthy behaviours".

If you're considering a weight-loss medication, your doctor can help you weigh the benefits and potential side effects based on your individual health profile, cardiovascular risk factors, and ability to tolerate side effects. The choice between maximum weight loss and heart protection, or between effectiveness and muscle preservation, depends on your personal health goals and medical history.