Adults with overweight or obesity lost an average of 14.9% of their starting body weight after 68 weeks of weekly semaglutide treatment in a major clinical trial. Participants receiving a placebo lost 2.4% on average. The results helped turn a diabetes medicine into the active ingredient behind one of the world’s most closely watched weight-management treatments. The STEP 1 trial, published in The New England Journal of Medicine, also found wide variation between patients, with some losing at least 20% and others responding far less.
That ingredient, semaglutide, is sold under several brand names. Ozempic is primarily prescribed for type 2 diabetes, while Wegovy is approved for long-term weight management in eligible patients. The products contain the same molecule but are prescribed for different purposes and may use different maintenance doses. Both have helped move medications that regulate appetite and blood sugar into mainstream discussion.
Their rise comes as obesity affects a large and growing share of the global population. The World Health Organization reports that more than 890 million adults were living with obesity in 2022, while worldwide adult obesity had more than doubled since 1990. Semaglutide offers an effective treatment option for some patients, but it also changes digestion, appetite signals, and glucose regulation in ways that can cause significant side effects.
How Semaglutide Changes Hunger and Blood Sugar
Semaglutide belongs to a group of medicines known as GLP-1 receptor agonists. GLP-1, short for glucagon-like peptide-1, is a hormone released by the intestines after food is eaten. It sends signals involved in digestion, appetite, and blood sugar control. Semaglutide activates the same receptors, allowing it to reproduce several of the hormone’s effects for much longer than naturally produced GLP-1. FDA prescribing information for Ozempic describes semaglutide as a GLP-1 receptor agonist used to improve glucose control in adults with type 2 diabetes.
When blood sugar rises, the medicine encourages the pancreas to release insulin, which helps move glucose from the bloodstream into cells. It also reduces glucagon, a hormone that normally tells the liver to release more glucose. These effects occur in a glucose-dependent way, meaning they become stronger when blood sugar is elevated. This mechanism allows semaglutide to improve glucose control while also addressing some of the metabolic problems associated with type 2 diabetes.
Semaglutide also slows the movement of food out of the stomach and affects appetite-related signals in the brain. Food can remain in the stomach longer, extending the feeling of fullness after a meal. Many patients become satisfied with smaller portions or experience fewer food cravings. Natural GLP-1 is broken down quickly, but semaglutide has a half-life of about one week. That longer activity supports its use as a once-weekly injection, usually given under the skin of the abdomen, thigh, or upper arm.
Weight-Loss Results Drove Worldwide Demand
Semaglutide’s weight-loss effects first became widely visible among people taking it for diabetes. Novo Nordisk later developed Wegovy as a higher-dose treatment for chronic weight management. The current FDA prescribing information for Wegovy covers its use for long-term weight reduction in eligible adults and younger patients, alongside reduced calorie intake and increased physical activity. Eligibility and reimbursement differ between countries, so access depends on local approval rules, health systems, and insurance coverage.
The STEP 1 trial tested weekly semaglutide at 2.4 milligrams in adults who had overweight or obesity but did not have diabetes. Both treatment and placebo groups received lifestyle support, which included guidance on calorie intake and physical activity. After 68 weeks, the difference in average weight loss between the groups was more than 12 percentage points. The trial showed that the drug’s results went beyond the smaller reductions previously observed with diabetes doses, although the treatment did not produce the same outcome for every participant.
Results depend on dosage, treatment duration, starting weight, health conditions, adherence, lifestyle support, and individual biology. Some patients lose a substantial amount of weight, while others lose relatively little or stop because they cannot tolerate the treatment. Weight can also return after treatment ends, so semaglutide is generally approached as long-term medical care rather than a brief course designed to produce permanent weight loss after a few injections.
Public interest grew faster than manufacturers could initially meet demand. The US Food and Drug Administration reported that injectable semaglutide products had been in shortage since 2022 because of increased demand. The agency declared the US shortage resolved in February 2025, but the episode showed how rapidly interest in weight-loss treatment could affect supplies intended for patients with diabetes and obesity. Availability has continued to vary across countries and healthcare systems.
Digestive Effects Are Common, While Serious Risks Are Less Frequent
Semaglutide’s effects on stomach emptying and food intake make gastrointestinal side effects the most frequent problems during treatment. Nausea, diarrhea, vomiting, constipation, abdominal pain, bloating, and indigestion are commonly reported.
Symptoms often appear while the dose is being increased and may improve as the body adjusts, but some patients experience persistent or severe reactions. In adult Wegovy weight-management trials, nausea affected about 44% of participants, diarrhea 30%, and vomiting and constipation roughly one-quarter each.
About 4.3% of adults receiving Wegovy in the trials permanently stopped treatment because of digestive reactions. Repeated vomiting or diarrhea can lead to dehydration, which may worsen kidney function in vulnerable patients. Severe constipation or continuing abdominal symptoms also require medical assessment rather than simply waiting for the discomfort to pass. The treatment is normally introduced through gradual dose increases to improve tolerance, but slower escalation cannot prevent every reaction.
A less common concern is acute pancreatitis, an inflammation of the pancreas that can cause severe, persistent abdominal pain, sometimes spreading to the back. Nausea and vomiting may occur at the same time. Cases of hemorrhagic, necrotizing, and fatal pancreatitis have been reported with GLP-1 medicines, although a report occurring during treatment does not by itself establish that semaglutide caused the condition. Current prescribing information advises stopping the medicine promptly when pancreatitis is suspected.
Gallstones and inflammation of the gallbladder are also recognized concerns. Rapid weight loss can independently raise the chance of developing gallstones, so both the medication and the pace of weight reduction may contribute. Other warnings include severe digestive reactions and possible worsening of diabetic retinopathy in some patients with existing eye disease. The balance of benefits and risks therefore depends on a person’s medical history, treatment goals, and ability to tolerate the medicine.
A Very Rare Eye Condition Has Been Added to Safety Information
European regulators concluded in June 2025 that NAION, short for non-arteritic anterior ischemic optic neuropathy, is a very rare adverse effect of semaglutide medicines. NAION develops when blood flow to the optic nerve is reduced, causing sudden vision loss that is usually painless. It commonly affects one eye at a time, although the other eye may later be affected. The condition is sometimes called an eye stroke because both involve interrupted blood supply, but it is not a stroke in the brain.
After reviewing clinical trial data, post-marketing reports, and published studies, the European Medicines Agency’s safety committee placed the estimated frequency at up to one case for every 10,000 people taking semaglutide. The committee recommended updating product information for Ozempic, Wegovy, and Rybelsus and stopping semaglutide if NAION is confirmed. Sudden loss of vision or rapidly worsening eyesight during treatment requires urgent medical attention.
This risk remains far less common than digestive side effects, but the potential consequence is more serious. Researchers are still examining which patients are most vulnerable and whether existing conditions affecting blood vessels or the optic nerve alter the risk. The regulatory decision does not mean that every vision problem during treatment is caused by semaglutide. It means the available evidence was strong enough to recognize NAION as a very rare adverse effect and add it to formal safety information.
Pregnancy Reports Do Not Show That Semaglutide Disables Birth Control
Reports of unexpected pregnancies among GLP-1 users have led to the phrase “Ozempic babies” on social media. The accounts have raised concerns about whether delayed stomach emptying interferes with oral contraceptives. However, a clinical pharmacology study indexed by PubMed found that once-weekly injectable semaglutide did not reduce the overall bioavailability of a combined pill containing ethinyl estradiol and levonorgestrel. The available evidence does not support the claim that semaglutide directly makes these contraceptives ineffective.
Other factors may explain some pregnancies reported during treatment. Vomiting or severe diarrhea can interfere with the absorption of any oral medicine, including a contraceptive pill. Weight loss and improved insulin sensitivity may also restore ovulation in people whose menstrual cycles were disrupted by obesity or polycystic ovary syndrome. These mechanisms are plausible, but an unexpected pregnancy does not prove that semaglutide directly increased fertility.
Semaglutide is not approved as a fertility treatment and should not be used during pregnancy for weight reduction. Current FDA information instructs patients to discontinue Wegovy when pregnancy is recognized. Because semaglutide remains in the body for several weeks, prescribing information also advises stopping treatment at least two months before a planned pregnancy.
Farid Amber is a Canada-based writer and Editor-in-Chief who covers technology, space, and the environment. With a strong technical background, he brings a clear and practical perspective to stories about innovation, science, and the future of our planet.
His education includes a diploma in Applied Science, a master’s degree in Industrial Electrical Engineering, and a diploma in Electromechanical Automated Systems. This gives him a deep understanding of how modern technologies work, from complex engineering systems to the ideas driving new discoveries.
As Editor-in-Chief, Farid focuses on making complex topics easy to read, accurate, and meaningful. His goal is to help readers understand not only what is happening in the world of science and technology, but why it matters.
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