Weight
Are weight-loss injections a shortcut? What the trials really show about GLP-1 medicines
Quick answer
Weight-loss injections work well, but they are not a shortcut on their own. In the STEP 1 trial, semaglutide plus lifestyle support led to 14.9% average weight loss over 68 weeks, against 2.4% with placebo. In SURMOUNT-1, the highest dose of tirzepatide led to about 20.9%. But when semaglutide was stopped, people regained about two-thirds of the weight they had lost within a year.
They are in the news, in the boardroom and probably in your group chat. Some colleagues call them a miracle. Others call them cheating. Neither is right. The evidence is strong, and it comes with conditions worth knowing before you start.
What the trials show
| Trial | Medicine | Who took part | Average weight change |
|---|---|---|---|
| STEP 1 (NEJM, 2021) | Semaglutide 2.4 mg weekly, 68 weeks | 1,961 adults with overweight or obesity, all given lifestyle support | −14.9% vs −2.4% with placebo |
| SURMOUNT-1 (NEJM, 2022) | Tirzepatide 5, 10 or 15 mg weekly, 72 weeks | 2,539 adults with obesity, without diabetes | About −15% to −20.9% by dose vs −3.1% with placebo |
In STEP 1, 86.4% of people on semaglutide lost at least 5% of their weight. The most common side effects in both trials were stomach-related, such as nausea, and were mostly mild to moderate.
What happens when you stop
In the STEP 1 extension (Diabetes, Obesity and Metabolism, 2022), people who stopped semaglutide regained about two-thirds of the weight they had lost within a year. They were still about 5.6% below their starting weight. This was an exploratory follow-up, but the message is clear: the medicine manages a long-term condition, it does not cure it.
What most people miss
Every person in STEP 1 received lifestyle support, including the placebo group. The medicine was added to healthy habits, not used instead of them. The people who do best long term are those who use the time on treatment to build habits that last: protein at meals, strength training to protect muscle, better sleep and a plan for stopping.
Questions to ask before you start
- Is it right for me? These medicines are prescribed for people who meet medical criteria. A proper assessment comes first.
- What is the plan for stopping? Agree how you will maintain your weight before you begin.
- How will I protect my muscle? Ask about strength training and enough protein.
- Who is monitoring me? Choose a regulated, doctor-led service, never an unverified online seller.
FAQs
How much weight will I lose on semaglutide? On average about 15% over 68 weeks in STEP 1, but results vary widely between people.
Will I have to take it forever? Many people regain weight after stopping. Discuss a long-term plan with your doctor.
Is it safe? Most side effects in trials were stomach-related and mild to moderate. Your doctor will check whether it is suitable for you.
For the years that matter, Dr Lwin
This article is general education, not personal medical advice. If you have symptoms or concerns, speak to your GP.