Inside Serena Williams’ 14kg weight loss: How GLP-1 injections work and 5 side effects to know

Recently, tennis legend Serena Williams opened up about using weight-loss medication, aiming to break the ‘stigma’ around such treatments. The 43-year-old, who has won 23 Grand Slam titles and is the epitome of athleticism, admits that after having children, she struggled to shed the extra pounds—just like many of us.

Speaking to the Today Show in the US, Williams described her extra weight as “an opponent.” Despite training five hours a day—running, biking, walking, and climbing stairs—she couldn’t defeat it the way she did on the tennis court. That’s when she decided to ‘try something different.’ Many of her friends were using GLP-1 medications, which help with weight loss, so she gave it a shot.

Williams emphasises that this wasn’t an easy route or a shortcut. Over eight months, she lost 31 lb (14 kg), but the results came with effort and commitment. Beyond weight loss, she says GLP-1 helped her regain energy, ease joint discomfort, stabilize blood sugar, and even boost mental well-being. “It was the medicine my body needed,” she explains, noting that traditional approaches simply weren’t enough anymore.

While this has brought about considerable backlash, do these injections under the brands, Ozempic, Mo and more, actually deliver results? Based on conversations with Lamya Kamal, a Dubai-based family medicine specialist and Zeenat Naseeb Abdul Wahid, Consultant Endocrinology, Medcare Hospital Sharjah, Hala Zakaria, Researcher at Zone Health and Nas Al Jafari, a Dubai-based functional medicinal specialist at DNA Health Clinic, we break it down.

These weight loss injections are a class of medications that help people lose weight by targeting specific hormones, involved in hunger regulation, fat metabolism and blood sugar control. Most of these medications are administered through subcutaneous injections, meaning they are injected just under the skin. These injections are typically taken once a week, though some medications may require daily administration.”

Experts explain that these medications tap into your body’s own hormonal system to help control hunger and manage blood sugar. They mimic two key hormones:

GLP-1 (glucagon-like peptide-1) – This hormone helps keep blood sugar in check and curbs your appetite by slowing how quickly food moves through your stomach.

GIP (glucose-dependent insulinotropic polypeptide) – This hormone triggers insulin release and supports appetite control, helping you feel full faster.

By imitating these hormones, the injections help people feel satisfied with smaller meals and reduce cravings, naturally leading to fewer calories consumed and gradual weight loss. They can also improve blood sugar levels, a major plus for those managing Type 2 diabetes.The popular weight-loss injections:

There are several injectable medications currently approved for weight loss.

There are several injectable medications currently approved for weight loss.

Key players: Wegovy, Saxenda, Mounjaro – what’s the difference?

If you’re hearing a lot about Wegovy lately, it’s because this once-weekly injection has transformed weight management.

How effective are they?

Wegovy is the brand name for semaglutide, a GLP-1 receptor agonist that helps control appetite and calorie intake. When paired with a lower-calorie diet and regular exercise, it delivers impressive results.

How effective is it? A 2021 New England Journal of Medicine study tracked 1,961 adults who were overweight or obese. Those on semaglutide 2.4 mg lost an average of 15.3% of their body weight over 68 weeks, compared to just 2.6% in the placebo group.

Who’s it for? It’s approved for adults with a BMI of 30 or more, or 27 with weight-related conditions.

2. Saxenda (Liraglutide)

Saxenda might sound familiar because it shares a similar approach to Wegovy. This daily injectable, also known as liraglutide, is another GLP-1 receptor agonist designed for chronic weight management. It works by curbing appetite and supporting healthier eating habits.

How well does it work? A 2015 New England Journal of Medicine study followed 3,731 participants who were overweight or obese. Those who received Saxenda 3.0 mg lost an average of 8% of their body weight over 56 weeks, compared to 2.6% in the placebo group.

Who can use it? Saxenda is approved for adults and adolescents aged 12 and older who are overweight or obese with related health conditions.

3. Mounjaro (Tirzepatide)

Meet the newcomer shaking up the scene: Mounjaro, powered by tirzepatide. What makes it different? It’s a dual-action drug, mimicking not just GLP-1 but also GIP hormones, giving it an edge in appetite control and insulin sensitivity.

How does it compare? In a 2022 Diabetes Care study, tirzepatide went head-to-head with semaglutide in people with Type 2 diabetes. The results? Participants on tirzepatide shed an average of 15 kg (33.1 lbs) over 72 weeks, outperforming semaglutide.

Who’s it for? While initially approved for Type 2 diabetes, it’s increasingly prescribed off-label for weight loss due to its strong results.

How Tirzepatide works

Tirzepatide targets two key hormones—GLP-1 and GIP—that naturally regulate appetite, food intake, and blood sugar. By amplifying their effects, it helps you feel full with smaller meals, reduces cravings (especially for sweets and fatty foods), slows stomach emptying, and improves how your body processes sugar. This dual action supports gradual weight loss while also helping control blood sugar.

Why it’s different

Unlike semaglutide, which targets only GLP-1, tirzepatide works on both GLP-1 and GIP receptors. This broader mechanism is believed to contribute to its slightly stronger weight-loss results, as noted by specialists Hala Zakaria and Nas Al Jafari.

Effectiveness

A 2023 JAMA Network study found that participants using tirzepatide lost an average of 25% of body fat within the first year—compared to about 15% for semaglutide users. For someone weighing 150 kg, this could mean losing roughly 30 kg versus 18 kg. These results are achieved alongside lifestyle measures, including a reduced-calorie diet (around 500 fewer calories per day) and at least 150 minutes of exercise per week. Individual results may vary, with some people losing more or less.

What are the side effects and who should avoid them?

As Ozempic use for weight loss surges, so do questions about its effects on lean mass, body weight that isn’t fat, including muscle. New mouse research suggests that while overall muscle mass may not drop as much as expected, muscle strength can still decline, highlighting a gap in understanding that needs urgent human studies.

The study, published in Cell Metabolism, found that roughly 10% of weight lost on Ozempic was lean mass, mostly from organs like the liver rather than skeletal muscles. Some muscles shrank slightly, but others stayed the same, and strength varied independently of size. Researchers note that fat loss naturally leads to some muscle reduction, but potential strength loss could be concerning for older adults, whose mobility and quality of life depend on muscle function.

Experts stress caution in extrapolating these findings to humans and call for clinical trials to clarify how weight loss drugs affect muscle size and strength.

 1. Common side effects (usually when starting or increasing the dose):

Individual responses vary:

Rare but serious side effects:

 Important precautions:

A new 2025 study from Washington University and the VA St. Louis Health Care System examined over 2 million people with diabetes taking GLP-1 receptor agonists (GLP-1RA), widely used for weight loss. Published in Nature Medicine, the research mapped 175 health outcomes, revealing benefits for cognitive and behavioral health, including lower risks of Alzheimer’s, dementia, seizures, addiction, suicidal thoughts, and certain psychiatric disorders. “These drugs act on brain receptors linked to impulse control and reward, which may explain their effects on appetite and addiction,” said senior author Dr. Ziyad Al-Aly in a statement.

However, the study also flagged increased risks for pancreatitis, kidney issues, and other complications. While most benefits were modest (10–20 per cent), they could be meaningful for conditions with few treatment options. Researchers emphasize that GLP-1RA works best alongside lifestyle changes and other interventions, underscoring the need for careful medical supervision.

Moreover, it's important to focus on whole, nutrient-dense foods such as fruits, vegetables, whole grains, lean proteins, and healthy fats. A helpful strategy is to start meals with protein, which can stabilise blood sugar levels and allows the person to feel fuller for longer, lowering the chances of overeating. Protein also plays a crucial role in preserving muscle mass during weight loss, making it an essential part of a balanced diet.

You need to engage in physical activity and resistance training to maintain muscle mass. And of course, a good sleep and stress management is always crucial for weight loss, explain the specialists.

As the specialists advise, even if you lose weight by using the injections, your habits ultimately define the success in a weight journey. Stopping the injections could result in the insulin resistance coming back, and if you do not engage in better diet and exercise, you could experience weight gain again. Similarly, ensure that your diet is protein rich, as this will aid muscle retention and support metabolic health. It is important to balance protein, fat and carb intake, to enhance the medication’s effectiveness.

Moreover, the FDA’s official website warns that unapproved versions of GLP-1 (glucagon-like peptide-1 receptor agonist) drugs can pose serious risks. Unlike approved medications, these products haven’t been reviewed for safety, effectiveness, or quality before hitting the market.