Wegovy, Ozempic and Mounjaro are among the most talked-about weight loss medications available today. But what can you actually expect? How quickly do they work, how much weight will you lose, and what happens when the scale stops moving? This article gives you an honest, plain-language overview based on the best clinical evidence.
How do GLP-1 medications work?
GLP-1 receptor agonists — including semaglutide (Wegovy, Ozempic) and tirzepatide (Mounjaro) — work by mimicking a hormone your body normally releases after eating. They reduce appetite, create a feeling of fullness sooner, and slow down how quickly your stomach empties. The result is that you eat less without necessarily feeling hungry.
This isn't just a standard appetite suppressant. These medications actually change the biological signalling that controls hunger and satiety — which is why they work for many people for whom diet alone hasn't been enough.
What do the clinical trials show?
Let's look at the real numbers from the major studies:
Semaglutide 2.4 mg (Wegovy) — the STEP 1 trial
In the large STEP 1 trial (published in the New England Journal of Medicine), participants lost an average of 14.9% of their body weight over 68 weeks (approximately 16 months) with semaglutide 2.4 mg. The placebo group lost only 2.4%. For a person weighing 220 lbs (100 kg), that equals roughly 33 lbs (15 kg) on average.
Tirzepatide (Mounjaro) — the SURMOUNT-1 trial
In the SURMOUNT-1 trial (also in NEJM), participants on the highest dose (15 mg tirzepatide) achieved an average weight loss of 20.9% over 72 weeks. At 10 mg it was 19.5%, and at 5 mg it was 15.0%. The placebo group lost 3.1%. Tirzepatide acts on two hormones (GLP-1 and GIP), which may explain the somewhat greater effect.
Timeline: when does weight loss happen?
Many people ask: "When will I start seeing results?" Here is a realistic timeline:
- Weeks 1–4: Most people notice reduced appetite fairly quickly. Some lose a little weight in the first month — typically 2–6 lbs (1–3 kg).
- Months 2–6: Weight loss accelerates. This is when most people see the most visible results. You are still titrating up in dose, and the body responds strongly.
- Months 6–12: Weight loss continues but the pace slows. You are nearing your maximum effective dose and beginning to reach a new equilibrium.
- After 12 months: Most people reach a plateau. Weight loss stalls — but this is not a sign the medication has stopped working; the body has simply adapted.
What is a weight loss plateau?
A plateau occurs when your body has adjusted its metabolism to your lower weight and reduced calorie intake. Your body is not "resisting" the medication — it has simply reached a new balance. Studies show that plateaus typically occur after 9–12 months on a stable dose.
It is important to know: even a plateau is a success. Maintaining a lower weight is just as important as losing it in the first place. Research shows that patients who continue treatment maintain their weight loss significantly better than those who stop.
What can you do about a plateau?
- Optimise your diet: Make sure you get enough protein (it protects muscle mass and keeps you fuller for longer).
- Move more: Even moderate amounts of exercise can help the body break through a plateau.
- Get enough sleep: Poor sleep increases hunger and can counteract the medication's effect.
- Talk to your doctor: In some cases, a dose increase or change in treatment may be worth considering.
Are results the same for everyone?
No — and it is important to have realistic expectations. Clinical trials show average figures, but there is significant variation. Some people lose 5%, others 25%. Factors such as starting weight, diet, exercise, sleep, genetics and other health conditions all play a role.
If you are not seeing the results you expected after 3–4 months on your target dose, it is a good idea to speak with your doctor. There may be underlying reasons — or a different treatment may suit you better.
What happens when you stop the medication?
It is well documented that many people regain a significant portion of the lost weight when they stop GLP-1 medication. The SURMOUNT-4 trial showed that patients who stopped tirzepatide regained an average of 14% of their body weight over the following 52 weeks — while those who continued lost a further 5.5%. This underlines that GLP-1 medication typically requires long-term treatment to maintain its effect.
Practical expectations — a quick summary
- Expect 10–20% weight loss over 1–1.5 years depending on the medication and dose
- Initial results are typically seen within the first couple of months
- A plateau after 9–12 months is normal and expected
- Weight loss requires long-term treatment to be maintained
- Diet, exercise and lifestyle still play an important role
Sources
- Wilding et al. (2021). Once-Weekly Semaglutide in Adults with Overweight or Obesity. NEJM (STEP 1).
- Jastreboff et al. (2022). Tirzepatide Once Weekly for the Treatment of Obesity. NEJM (SURMOUNT-1).
- NHS England. Weight management injections.
- Mayo Clinic. Semaglutide (subcutaneous route).
- Tremblay & Chaput (2023). Physiology of the Weight Loss Plateau. PMC/NCBI.