Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Many people notice great results with weight loss injections, while others seem stuck at the same number. What causes that difference, and what can you actually do about it?
Clinical data shows that while medications like Ozempic (semaglutide) and Mounjaro (tirzepatide) can help people lose an average of 13.7% and 20.2% of their body weight, respectively over time, not everyone experiences the same success. In fact, research found that around 10–17% of people using semaglutide were ‘non-responders’, losing less than 5% of their starting weight during clinical trials. These injections can be powerful tools, but only when used consistently and paired with healthy habits.
Weight loss injections, such as Mounjaro, Ozempic, Wegovy, or Saxenda, work by mimicking hormones in your body that regulate appetite and blood sugar. These medications activate GLP-1 (glucagon-like peptide-1) or dual GLP-1/GIP receptors, which signal your brain to feel full sooner and slow down digestion.
These injections can help reduce calorie intake and support significant weight loss when combined with lifestyle changes. For example, a 2023 study found participants lost an average of 15–20% of their body weight after consistent use over 68 weeks, alongside a healthy diet and exercise plan.
But remember: these injections support your efforts; they don’t replace them.
Sometimes, it’s not the medication that’s failing, but rather other factors that are quietly sabotaging your progress. Here are the most common ones:
Most treatments begin with a small dose to minimise side effects like nausea. This means the early weeks may not show dramatic changes. According to clinical trial data, semaglutide doses are gradually increased over about 16 weeks before reaching the full maintenance level, meaning it can take around 12–16 weeks for your dose and body response to stabilise enough for noticeable results.
Skipping doses or taking them irregularly disrupts your hormone response. GLP-1 levels drop quickly when you miss a shot, which can increase hunger and reduce the medication’s overall effect.
Even with appetite suppression, weight loss still depends on burning more energy than you consume. Overeating, even slightly, can cancel out the medication’s impact.
Dressings, sauces, fancy coffees, and ‘healthy’ snacks can sneak in hundreds of extra calories daily. A latte here, a drizzle of olive oil there—it all adds up.
While GLP-1s lower appetite, they don’t burn calories directly. Studies show combining injections with regular exercise leads to double the fat loss compared to medication alone.
Less than 7 hours of sleep can disrupt hormones like ghrelin and leptin, which control hunger and fullness. Poor rest also reduces willpower and recovery, making it harder to stay consistent.
Stress triggers cortisol release, which can increase appetite and fat storage, especially around the belly. Chronic stress may also blunt your body’s insulin sensitivity, slowing progress.
Thyroid issues, PCOS, or insulin resistance can make losing weight harder, even with medication. If your progress has plateaued despite effort, it’s worth checking in with your doctor.
Certain antidepressants, steroids, or birth control pills can counteract weight loss efforts. Always discuss all your prescriptions with your healthcare provider.
As you lose weight, your metabolism naturally slows down. This plateau phase is completely normal but can feel discouraging. Adjusting your calorie intake or exercise intensity often helps restart progress.
Small, consistent habits often make or break your results. Here’s how to make your medication work its best.
Take your medication consistently. Set a reminder or link it to a routine (like brushing your teeth). Consistency is key for stable appetite control and blood sugar regulation.
Follow a balanced, portion-controlled diet. Pair your injection with nutrient-dense foods like lean proteins, whole grains, vegetables, and healthy fats. Eating slowly and mindfully helps prevent overeating.
Prioritise protein and fibre in meals. Protein supports muscle retention, while fibre keeps you fuller for longer. Aim for 25–30 grams of fibre and 1.2–1.6 grams of protein per kg of body weight daily.
Stay physically active with regular exercise. Include both cardio and strength training. Studies show resistance training helps preserve lean muscle during weight loss, which keeps metabolism higher.
Drink enough water daily. Dehydration can mimic hunger. Aim for around 2–3 litres of water daily, or more if you’re active or live in a hot climate.
Get adequate sleep each night. Good sleep improves appetite regulation and recovery. Try sticking to a consistent bedtime and limit screens an hour before bed.
Manage stress effectively. Try yoga, walking, journalling, or even short breathing exercises. Reducing stress helps control cortisol and cravings.
Track progress with logs and measurements. Weight isn’t the only metric. Measure waist circumference, take progress photos, and note how your clothes fit. Tracking helps you spot trends that the scale might miss.
Avoid excess alcohol and sugary drinks. These liquid calories can easily derail progress. Alcohol can also affect sleep quality and appetite control, reducing your medication’s effectiveness.
Sometimes, it’s not just the medication. Your daily habits can make all the difference. Read this article on what to eat while taking weight loss injections for practical strategies to maximise your results.
Sometimes, you need a little expert guidance to get things moving again. Consult a professional when you experience any of these signs:
No weight loss after several months of use
Experiencing severe or persistent side effects
Difficulty staying consistent with medication
Unexplained weight gain despite proper use
Signs of underlying medical conditions
Concerns about medication interactions
Questions about adjusting your dose
Uncertainty about long-term results
Your doctor may review your dosage, assess any other health issues, or refer you to a dietitian for more personalised support.
If your weight loss injection isn’t working, don’t panic; it’s often just a matter of fine-tuning your habits and dosage. With consistent use, mindful eating, regular activity, and proper medical guidance, you can unlock the full potential of your medication and keep the results long-term.
Dr Nick Fuller is the founder of Interval Weight Loss and is a leading obesity expert at the University of Sydney with a Ph.D. in Obesity Treatment. Dr Fuller is also the author of three best-selling books and his work been published in top ranked journals in the medical field, including JAMA, Lancet and American Journal of Clinical Nutrition.