Clinically reviewed by Dr. Ponlawat Pitsuwan, Physician, Doctor Bangkok. Last reviewed: July 2026
Semaglutide is a GLP-1 receptor agonist, a medicine that mimics a natural gut hormone. It reduces appetite, slows stomach emptying and helps control blood sugar, so you feel full on less food. It is the active ingredient in Ozempic and Wegovy, given as a weekly injection under medical supervision.
Behind the brand names Ozempic and Wegovy sits a single active ingredient: semaglutide. Patients often arrive knowing the brand but not the science, so in this guide I explain what semaglutide actually is, how it produces weight loss, and what a sensible course of treatment looks like.
Understanding the mechanism helps you use the medicine well and set realistic expectations. As a physician in central Bangkok, I find that patients who grasp how it works tend to tolerate it better and stick with the plan.
What is semaglutide?
Semaglutide is a GLP-1 receptor agonist. GLP-1 is a hormone your gut naturally releases after eating, but the natural version breaks down within minutes. Semaglutide is engineered to last around a week, which is why a single weekly injection can keep its effects going. It is the active ingredient in both Ozempic and Wegovy.
How does it work for weight loss?
Semaglutide works in several ways at once. It acts on appetite centres in the brain to increase fullness, it slows how quickly the stomach empties so you feel satisfied longer, and it helps regulate blood sugar. Together these effects reduce how much you want to eat, which is what drives the weight loss. It is a treatment that supports better eating, not a licence to ignore diet entirely.
How semaglutide compares with tirzepatide
Semaglutide acts on the GLP-1 pathway alone. Tirzepatide (Mounjaro) adds a second pathway, GIP, and tends to show greater average weight loss in trials. Which suits you depends on your health and tolerance; our Ozempic vs Mounjaro comparison covers this in full.
What to expect on treatment
Semaglutide is started at a low dose and increased gradually over weeks. This titration is deliberate: it lets your body adjust and reduces nausea. Your doctor will advise the exact schedule. It is a weekly self-injection with a pen, and our injection guide walks through the technique.
Side effects and who should not take it
The most common side effects are digestive and usually ease with time. Semaglutide is not suitable for everyone, including people with certain thyroid tumours, a history of pancreatitis, or those who are pregnant. Full details are in our guide to GLP-1 side effects and the eligibility criteria.
When to see a doctor
Seek prompt care for severe abdominal pain that may spread to the back, persistent vomiting, dehydration, or an allergic reaction. If you take diabetes medication, be alert to low blood sugar. Screening before starting and supervision during treatment are how these risks are managed, and our 24/7 clinic can review you quickly if needed.
Curious whether semaglutide could work for you? Begin with a screening consultation. Read our overview of weight-loss injections in Bangkok or contact the clinic.
Frequently asked questions
Is semaglutide the same as Ozempic?
Semaglutide is the active ingredient; Ozempic and Wegovy are brand names that contain it. Ozempic is licensed for diabetes and used for weight, while Wegovy is a higher-dose version for weight loss.
How is semaglutide given?
As a once-weekly injection under the skin using a pre-filled pen, started low and increased gradually as your doctor advises.
Does it work without diet changes?
It reduces appetite, which makes eating less easier, but it works best alongside sensible eating and activity rather than replacing them.
How long do people stay on it?
This is individual. Because appetite tends to return after stopping, we plan for the longer term rather than a brief course.
Is it safe?
It is well-studied and widely used, but not suitable for everyone. That is why medical screening before starting is essential.
Dr. Ponlawat Pitsuwan
Physician, Doctor Bangkok
Dr. Ponlawat is a physician at Doctor Bangkok, a private medical clinic in central Bangkok. He explains and prescribes semaglutide as part of a supervised weight-management programme.
Dr. Ponlawat Pitsuwan is a physician at Doctor Bangkok, a private clinic in central Bangkok. He sees expats, residents, and medical tourists for general medicine, wellness consultations, and IV therapy. His focus is straightforward, evidence-based care delivered in plain language.