By Dr. Asnat Raziel, bariatric surgeon specializing in obesity treatment, metabolic health and healthy longevity; Director of the Multidisciplinary Center for Obesity Treatment, Assia Medical, Assuta Ramat HaChayal, Tel Aviv
Ozempic (semaglutide): what to know before you start
Ozempic (semaglutide) is a once-weekly injection originally developed to treat type 2 diabetes. Its active ingredient is semaglutide, and Ozempic is the brand name. Over the years, it has become clear that this medication does far more than control blood sugar: it helps people lose weight, protects the heart and slows kidney damage.
Semaglutide represents a profound shift in how we think about treatment. Rather than focusing on weight alone, it acts on the biological system that drives hunger, fullness and energy balance. In this guide, you will learn what the medication does, what the research has shown, how it is used and who it is right for.
Who is Ozempic (semaglutide) for?
Ozempic’s official indication is type 2 diabetes in adults. In the United States, the FDA has approved it for three purposes. First, to improve blood sugar control alongside diet and exercise. Second, to reduce cardiovascular events in people with diabetes and heart disease. Third, in January 2025, an indication was added for slowing chronic kidney disease in people with diabetes.
For treating obesity without diabetes, there is a dedicated product containing the same active ingredient: Wegovy. The main differences are the dose and the official indication. If you prefer a pill, you may consider Rybelsus for diabetes, or the Wegovy pill for obesity.
How it works: not just fullness, but a brain–metabolic shift
Ozempic belongs to a class of drugs called GLP-1 receptor agonists. GLP-1 is a natural incretin hormone that the gut releases in response to eating, and it affects many systems throughout the body.
Semaglutide mimics this hormone and triggers several mechanisms at once. It boosts insulin release, but only when blood sugar is high. It also reduces glucagon secretion, so the liver produces less glucose. And it slows the rate at which the stomach empties.
The most important effect, however, happens in the brain. The medication acts on the satiety and reward centers in the hypothalamus and the limbic system. This reduces hunger, weakens the drive to eat and quiets “food noise.” As a result, many patients experience a new sense of control over their eating.
Ozempic (semaglutide) and weight loss: how effective is it?
The scientific basis for weight loss with semaglutide comes from the STEP trials. In these studies, participants received 2.4 mg a week, which is the Wegovy dose. The figures below therefore reflect what the active ingredient can achieve at the obesity dose.
- STEP 1: The trial enrolled 1,961 adults without diabetes. After 68 weeks, average weight loss reached 14.9% of body weight, compared with 2.4% in the placebo group.
- STEP 3: Here, researchers added intensive behavioral therapy. Average weight loss reached 16%, versus 5.7% with placebo.
- STEP 5: Follow-up lasted two years. At week 104, weight loss stood at about 15.2%, compared with about 2.6% with placebo.
In people with diabetes, the results are somewhat more modest. In STEP 2, for example, average weight loss was 9.6%, compared with 3.4% with placebo. At Ozempic doses of up to 2 mg, weight loss is usually smaller than at 2.4 mg.
Beyond weight, the researchers documented consistent improvements in cardiometabolic markers, including lower blood pressure, lower triglycerides and reduced markers of inflammation such as CRP.
Effects on the heart and kidneys
The SUSTAIN-6 trial included 3,297 people with diabetes at high cardiovascular risk. The risk of a major cardiovascular event fell by 26% (hazard ratio 0.74). Such events include heart attack, stroke and cardiovascular death.
The SELECT trial studied 17,604 people with overweight or obesity and heart disease, but without diabetes. The risk of cardiovascular events fell by 20% (6.5% vs. 8.0%). This trial used the 2.4 mg dose. Its findings position semaglutide as a preventive tool, not merely a weight-loss drug. I discuss this in more detail in my article on semaglutide and the heart.
In addition, the FLOW trial included 3,533 people with diabetes and chronic kidney disease. Ozempic at 1 mg reduced the risk of worsening kidney disease, kidney failure and cardiovascular death by 24%.
Broader benefits: fatty liver, sleep and overall health
Semaglutide’s impact reaches beyond the classic measures. At 2.4 mg, it improved liver health in people with inflammatory fatty liver disease (MASH), and in August 2025 the FDA approved Wegovy for this indication. Weight loss also often improves sleep apnea and uric acid levels.
There are also hints of effects on the brain, including protection against cognitive decline. However, this area is still under study, and there is currently no definitive proof.
How to use Ozempic (semaglutide): simple, but it needs fine-tuning
Ozempic is given as a subcutaneous injection once a week, using an easy-to-use pen. You can inject it at any time of day, with or without food, but it is best to stick to the same day each week.
Treatment starts at 0.25 mg a week for four weeks, then moves up to 0.5 mg. After that, your doctor may increase the dose to 1 mg and then to 2 mg, depending on blood sugar control and how well you tolerate it. Increasing the dose gradually reduces side effects and gives your body time to adjust.
Side effects and safety
Most patients tolerate the treatment well. The most common side effects involve the digestive system: nausea, a feeling of fullness, vomiting, diarrhea or constipation. These usually pass and are related to the dose and the adjustment period.
There are also rare risks, including pancreatitis, gallstones and temporary worsening of diabetic retinopathy. In SUSTAIN-6, for example, retinopathy complications occurred in 3% of patients, compared with 1.8% with placebo.
In June 2025, the European Medicines Agency concluded that NAION is a very rare side effect of semaglutide. NAION is damage to the optic nerve that can cause vision loss. It occurs in up to 1 in 10,000 patients. Any sudden loss of vision therefore requires immediate medical attention.
The medication must not be used during pregnancy, or by people with a history of medullary thyroid cancer or MEN2 syndrome. Careful patient selection and regular medical follow-up are therefore an essential part of treatment.
Long-term treatment: not a magic bullet
Ozempic changes the biology of hunger and fullness, but it does not work in a vacuum. To succeed, patients combine personalized nutrition, regular physical activity and good-quality sleep. Working on eating patterns and behavior strengthens the results even further.
When all of these come together, the result is more than weight loss. It is a genuine lifestyle change that helps you hold on to what you have achieved. In my clinic, Ozempic (semaglutide) is part of a multidisciplinary program that includes a dietitian and behavioral support.
The bottom line
Ozempic (semaglutide) marks a true revolution in the treatment of type 2 diabetes, with proven benefits for weight, the heart and the kidneys. The weekly injection is simple to use and backed by large clinical trials. Even so, long-term success requires guidance, close follow-up and lasting lifestyle change.
The information in this article is general information only and is not a substitute for personal medical advice. Treatment decisions should be made together with your doctor.
Frequently asked questions about Ozempic (semaglutide)
Is Ozempic only for people with diabetes?
Its official indication is type 2 diabetes. High-dose semaglutide, sold as Wegovy, is also approved for obesity. In practice, doctors sometimes use Ozempic for weight management as well, based on their clinical judgment.
How long does it take to see weight loss?
Sometimes within the first few weeks. However, significant weight loss develops over months, and in clinical trials it peaks after about a year of treatment.
Does the weight come back after stopping treatment?
In most cases, yes. When treatment stops, the body’s biology returns to its previous state. That is why it is a good idea to plan ahead for maintaining your weight after stopping GLP-1 medication.
Do I need to diet while on treatment?
Yes, but not an extreme diet. It is important to eat enough protein and preserve muscle mass. Nutritional adjustments make the most of the window of opportunity the medication creates.
Can anyone take Ozempic?
No. There are contraindications, so a full medical evaluation is needed before starting treatment.
What is the difference between Ozempic and Wegovy?
Both are based on semaglutide. Ozempic goes up to 2 mg and is intended for diabetes. Wegovy goes up to 2.4 mg, and in some countries 7.2 mg, and is intended for obesity.
Is this a lifelong treatment?
In many cases, yes. Obesity and diabetes are chronic diseases, and treating them requires a long-term approach.
References
Semaglutide Treatment Effect in People With Obesity – STEP 1
Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial
Semaglutide Improves Weight Loss in Patients With Diabetes (STEP 2)
Semaglutide Effects on Cardiovascular Outcomes in People With Overweight or Obesity – SELECT
