Dr Nick Fuller
Leading Obesity Expert at the University of Sydney and founder of Interval Weight Loss.
Semaglutide has been making headlines as a breakthrough medication for weight loss. But it wasn’t originally made for shedding kilos. It first entered the scene as a treatment for type 2 diabetes, and researchers soon noticed something else: patients were also losing a significant amount of weight. In clinical trials involving individuals classified as overweight or obese based on their BMI, those who received weekly semaglutide injections lost an average of 16% of their body weight over a 68-week period. Fast forward a few years, and now semaglutide is being used worldwide to support people struggling with obesity and long-term weight management.
If you're wondering how it works, what it's actually used for, and whether it’s a good fit for you, this guide breaks it all down.
Semaglutide is a medication that mimics a hormone your body already produces called GLP-1 (glucagon-like peptide-1). This hormone plays a key role in regulating blood sugar levels, insulin production, and appetite. Semaglutide is sold under different brand names depending on its use. For diabetes, it’s known as Ozempic, and for weight loss, it’s Wegovy.
It belongs to a class of drugs called GLP-1 receptor agonists. In short, it helps your body respond better to food by slowing digestion, reducing hunger, and helping you feel full for longer.
Semaglutide works by binding to GLP-1 receptors in your brain and pancreas. Here’s what that does:
It tells your pancreas to release insulin when your blood sugar is high
It slows down the movement of food through your stomach
It sends signals to your brain to reduce appetite
In clinical terms, it improves glycaemic control while supporting appetite regulation — two big drivers of long-term weight management.
Below are the key ways it’s currently being used.
Semaglutide helps lower blood glucose levels by increasing insulin secretion and reducing the amount of sugar released by the liver. It’s been shown to significantly reduce HbA1c levels, a marker of long-term blood sugar control.
In trials like STEP 1, participants taking semaglutide lost an average of 14.9% of their body weight over 68 weeks — far more than those in the placebo group.
Semaglutide has also been found to lower the risk of major cardiovascular events (like heart attacks or strokes) in people with type 2 diabetes who have established heart disease.
By improving insulin response and reducing glucagon (a hormone that raises blood sugar), semaglutide keeps glucose levels in check, particularly after meals.
One of the most talked-about effects: it curbs cravings by influencing hunger signals in the brain.
Semaglutide delays gastric emptying, meaning food stays in your stomach longer, leading to prolonged fullness and fewer spikes in blood sugar.
Thanks to its unique effects on appetite and metabolism, semaglutide offers several benefits for people looking to lose weight or manage chronic conditions like type 2 diabetes.
Helps with weight loss
Clinical trials show that people using semaglutide for weight loss can shed 10–15% of their body weight, depending on dose and duration.
It reduces both fasting and post-meal blood glucose levels, helping people with type 2 diabetes maintain better control without as many fluctuations.
By acting on appetite centres in the brain, semaglutide helps reduce the desire to snack or overeat. This is often the hardest part of weight loss.
According to the SUSTAIN-6 trial, semaglutide lowered the risk of cardiovascular death, heart attack, or stroke by 26% in high-risk patients with type 2 diabetes.
It enhances how your body reacts to insulin, especially after meals, which helps stabilise energy and prevent sugar crashes.
Unlike fad diets, semaglutide targets the biological systems that make weight regain so common, making it more sustainable when used alongside lifestyle changes.
It stimulates GLP-1 receptors in the gut and brain, making people feel satisfied sooner and stay full longer after eating.
Like any medication, semaglutide isn’t without side effects. The most common are related to the digestive system:
Nausea
Vomiting
Diarrhoea
Constipation
Headache
Fatigue
Dizziness
Abdominal pain
Indigestion
Bloating
Belching
Loss of appetite
Injection site reactions
Less common but more serious risks include:
Low blood sugar (especially if taken with other diabetes meds)
Gallbladder problems
Kidney issues
Pancreatitis
Always speak to your doctor if you experience unusual or persistent symptoms.
Semaglutide has been approved for weight loss in:
Adults with a BMI of 30 or higher (classified as obesity)
Adults with a BMI of 27 or higher who also have a weight-related condition like high blood pressure, type 2 diabetes, or high cholesterol
People who have struggled with weight loss through diet and exercise alone
Adults under the supervision of a GP or obesity specialist
It’s not a quick-fix solution, but it can offer real results when paired with long-term lifestyle changes.
Semaglutide is not suitable for everyone. It should be avoided by:
Pregnant or breastfeeding women
People with a history of medullary thyroid carcinoma
Those with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
Individuals allergic to Semaglutide or any of its ingredients
Anyone with a history of pancreatitis
Children and teens under 18
People with severe gut conditions unless medically cleared
Always consult your doctor before starting any new treatment.
Semaglutide works on several pathways in the body to support weight loss.
1. Reduces Appetite: It decreases hunger hormones like ghrelin, so you feel less inclined to snack or overeat.
2. Slows Down Digestion: Food stays in your stomach longer, reducing the urge to eat soon after meals.
3. Increases Feelings of Fullness: It boosts satiety signals to the brain, making you feel full with smaller portions.
4. Lowers Calorie Intake: The combination of reduced hunger and smaller meals naturally cuts your daily intake.
5. Controls Blood Sugar Levels: More stable blood sugar means fewer cravings, especially for high-carb comfort foods.
6. Supports Long-Term Weight Management: By working on the underlying biological drivers of obesity, it offers a long-term strategy, not just a short-term fix.
Some people notice reduced appetite within the first few weeks, while weight loss tends to become more noticeable by week 8 to 12. Clinical trials showed peak weight loss at around 68 weeks, but individual results vary.
Keep in mind: this isn’t an overnight solution. It works best when used consistently, alongside a supportive nutrition and movement plan.
Semaglutide is changing the game for people who’ve been stuck in the cycle of losing and regaining weight. Backed by solid science and used under medical supervision, it offers a new pathway for long-term weight management, especially for those with obesity or related health conditions.
Still, it’s not a magic solution. Like any tool, it works best when paired with meaningful lifestyle changes and personalised support from a healthcare professional.
Thinking about trying semaglutide?
Before you commit, check out this article exploring whether weight loss injections are worthwhile. It breaks down the pros, the cons, and what to consider for long-term success.
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.