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Semaglutide Explained: How Ozempic and Wegovy Work in Your Body

Semaglutide, the drug in Ozempic and Wegovy, does more than curb appetite. Here's how it works in your body and what major trials show for heart, kidney, and liver health.

Semaglutide: what it is and how it works in your body

The best-known medicine of its kind, with the longest track record: one copied gut hormone, and effects that reach from your brain to your kidneys. Here is what the research actually shows, in plain language.

Peptide Advocate · Evidence review · Updated September 2026

What it isA lab-made, longer-lasting version of GLP-1, a natural gut hormone
Brand namesOzempic and Rybelsus (type 2 diabetes); Wegovy (weight, heart, and liver)
How it's takenA weekly injection under the skin, or a daily pill
Headline resultAbout 15% average weight loss at the 2.4 mg dose in a 68-week trial6

What is semaglutide?

Semaglutide is a prescription medicine made by Novo Nordisk. It is a peptide, a short chain of 31 amino acids, and it is 94% identical to GLP-1 (glucagon-like peptide-1), a hormone your gut releases after you eat.4 Natural GLP-1 lasts only about two minutes in the blood. Semaglutide was engineered to last much longer. An amino acid swap blocks the enzyme that normally cuts GLP-1 apart, and a fatty-acid "tail" grips albumin, a protein in your blood. Together, these changes stretch its half-life to about a week.5

The pill versions pair semaglutide with an absorption enhancer that protects it in the stomach and helps it pass into the bloodstream.4 Pills are taken daily on an empty stomach, because food blocks absorption.

FDA-approved uses (as of September 2026)

  • Ozempic (weekly injection): blood sugar control in adults with type 2 diabetes; lowering the risk of heart attack, stroke, and cardiovascular death in adults with type 2 diabetes and heart disease; and, since January 2025, lowering the risk of kidney failure, major kidney decline, and cardiovascular death in adults with type 2 diabetes and chronic kidney disease.3
  • Rybelsus (daily pill): blood sugar control in type 2 diabetes, with a cardiovascular risk-reduction approval added in October 2025.24
  • Wegovy (weekly injection, and since December 2025 a daily 25 mg pill): long-term weight management in adults with obesity, or overweight plus a weight-related condition; lowering cardiovascular risk in adults with heart disease and obesity or overweight; and treating fatty-liver inflammation (MASH) with moderate to advanced scarring, under accelerated approval.1,2,24 A higher 7.2 mg dose, Wegovy HD, was approved in March 2026 for people who have already tolerated 2.4 mg.20

How it works: one hormone signal, many tissues

When you eat, cells in your intestines release GLP-1. It tells your pancreas to release insulin, tells your stomach to slow down, and tells your brain you've eaten. Semaglutide activates the same GLP-1 receptor, but around the clock, all week long.

That single-receptor design is the key difference from tirzepatide (Mounjaro, Zepbound), which also activates a second hormone receptor called GIP. Semaglutide does its work through GLP-1 alone, and GLP-1 receptors are found in the pancreas, brain, gut, heart, blood vessels, and kidneys.5

Why semaglutide lasts a weekNatural GLP-1 is cut apart by the DPP-4 enzyme within minutes. Semaglutide has a swapped amino acid that blocks the enzyme and a fatty-acid tail that binds albumin in the blood, so it lasts about a week and keeps activating the GLP-1 receptor.Natural GLP-1DPP-4 enzyme cuts it hereBroken down in about 2 minutesSemaglutidealbumin(blood protein)swapped amino acidblocks the enzymefatty-acid tail gripsalbuminLasts about 1 weekGLP-1 receptorOutside the cellInside the cellOne receptor, many tissues: more insulin and less glucagon when blood sugar is high,slower stomach emptying, and stronger fullness signals in the brain
How semaglutide is engineered to last a week, and the receptor it acts on. Diagram: Peptide Advocate.

A tour of the body

Some of semaglutide's effects come directly from GLP-1 receptors in that tissue. Others show up as fewer heart attacks, slower kidney decline, and healthier livers in long-term outcome trials, where weight loss is only part of the explanation.

Where semaglutide acts in the bodyBody outline with callouts for brain, blood vessels, liver, kidneys, heart, stomach, pancreas and fat tissue.BrainQuiets hunger signals andfood cravings; you feelfull soonerBlood vesselsLower blood pressure andinflammation (CRP); heartbenefit starts earlyLiverFDA-approved for fatty-liver inflammation (MASH)with scarringKidneys24% fewer serious kidneyevents in people withdiabetes and kidney diseaseHeart20% fewer heart attacks,strokes and CV deaths inpeople with heart diseaseStomachEmpties more slowly, someals feel bigger andlast longerPancreasMore insulin when sugaris high, less glucagon;lowers A1CFat tissueAbout twice as much fatlost as lean mass;less belly (visceral) fatdirect GLP-1 effectbenefit shown in outcome trials
Where semaglutide acts, and what studies have found in each area. Green marks direct GLP-1 effects; teal marks benefits shown in outcome trials. Diagram: Peptide Advocate.

Brain: appetite and cravings

GLP-1 receptors in the brain's appetite centers help turn down hunger and increase the feeling of fullness.5 Many people describe eating smaller portions, feeling satisfied sooner, and thinking about food less often. This is the main driver of weight loss.

Stomach and gut: slower emptying

Semaglutide slows how fast food leaves your stomach, so a meal feels bigger and fullness lasts longer. The same effect causes the most common side effects: nausea, fullness, constipation, and diarrhea. It can also change how quickly some pills you swallow are absorbed.1

Pancreas: blood sugar control

Semaglutide helps the pancreas release insulin, and lowers glucagon (a hormone that raises blood sugar), but only when blood sugar is elevated.5 Because of that built-in brake, it rarely causes low blood sugar by itself; the risk rises when it's combined with insulin or sulfonylureas.

Fat tissue: mostly fat, including belly fat

In a body-scan substudy of STEP 1, people on semaglutide lost 19.3% of their total fat mass and 27.4% of their visceral (deep belly) fat. Lean mass fell 9.7%, but because fat fell faster, the share of the body made up of lean mass actually rose.7 Some lean-mass loss happens with any large weight loss, which is why protein intake and strength training matter during treatment.

Liver: fatty-liver inflammation

In the first part of the ESSENCE trial, adults with MASH (the inflammatory form of fatty liver disease) and moderate to advanced scarring took semaglutide 2.4 mg or placebo for 72 weeks. Liver inflammation resolved without scarring getting worse in 62.9% of people on semaglutide versus 34.3% on placebo, and scarring improved in 36.8% versus 22.4%.18 That led to accelerated FDA approval in August 2025. The second part of the trial, which will show whether it prevents cirrhosis and other liver events, is expected to report in 2029.17

Heart and blood vessels

SELECT followed 17,604 adults with heart disease and overweight or obesity, none with diabetes, for about three years. Heart attack, stroke, or cardiovascular death occurred in 6.5% of people on semaglutide versus 8.0% on placebo, a 20% lower risk.10,11 Interestingly, the benefit appeared early, before much weight had been lost, and one analysis estimated that only about a third of it was explained by a smaller waistline.11,13 Researchers suspect effects on inflammation, blood pressure, and blood vessel health also contribute.

For people with obesity and a common type of heart failure (HFpEF), the STEP-HFpEF trial of 529 adults found that semaglutide improved heart-failure symptoms and physical limits, lengthened walking distance, and lowered the inflammation marker CRP over one year.19

Kidneys

FLOW was the first large trial of a GLP-1 medicine built specifically around kidney outcomes. In 3,533 adults with type 2 diabetes and chronic kidney disease, semaglutide lowered the risk of kidney failure, major loss of kidney function, or death from kidney or heart causes by 24%, and slowed the yearly decline in kidney function.15,16 In SELECT, among people without diabetes, a composite of serious kidney outcomes was also less common with semaglutide.14 One caution: vomiting or diarrhea can cause dehydration, which can injure the kidneys, so drinking enough fluids matters.1

Brain health: a clear "not proven." Semaglutide was tested for early Alzheimer's disease in two large trials, EVOKE and EVOKE+, with 3,808 participants over two years. Although some Alzheimer's-related blood markers improved, the pill did not slow memory or functional decline compared with placebo.22 Be skeptical of claims that semaglutide protects the brain.

What the major trials found

Semaglutide has been studied in more than a dozen large trials: SUSTAIN and PIONEER (type 2 diabetes), STEP (weight management), and dedicated trials for heart, kidney, and liver outcomes.

Average weight loss with semaglutide 2.4 mgSTEP 1 at 68 weeks: placebo 2.4 percent, semaglutide 14.9 percent. SELECT at 4 years: placebo 1.5 percent, semaglutide 10.2 percent.Average weight lost on semaglutide 2.4 mgEach trial compared semaglutide with placebo in the same group of people0%−5%−10%−15%−20%STEP 1 · 68 weeks−2.4%Placebo−14.9%SemaglutideSELECT · 4 years−1.5%Placebo−10.2%SemaglutideSELECT enrolled people with heart disease and did not focus on weight loss. Sources: Wilding, NEJM 2021; Ryan, Nat Med 2024.
Weight loss in a 68-week weight-management trial and a four-year heart trial. These are averages; individual results vary widely.6,12
TrialWho was studiedKey finding
STEP 11,961 adults with obesity or overweight, no diabetes; 68 weeks14.9% average weight loss vs. 2.4% on placebo6
STEP 4803 adults after a 20-week lead-inStopping led to weight regain (see below)9
STEP UP1,407 adults with obesity; 72 weeks20.7% average weight loss on the 7.2 mg dose20
SURMOUNT-5751 adults with obesity; head-to-head vs. tirzepatide13.7% average weight loss on semaglutide vs. 20.2% on tirzepatide at 72 weeks21
SELECT17,604 adults with heart disease and overweight or obesity, no diabetes20% lower risk of heart attack, stroke, or CV death10
FLOW3,533 adults with type 2 diabetes and kidney disease24% lower risk of major kidney events or kidney/CV death15
ESSENCEAdults with MASH and moderate to advanced liver scarringLiver inflammation resolved in 62.9% vs. 34.3% on placebo18
STEP-HFpEF529 adults with obesity and HFpEF heart failureBetter symptoms, walking distance, and inflammation markers19
EVOKE / EVOKE+3,808 adults with early Alzheimer's diseaseNo slowing of decline vs. placebo22

What happens if you stop?

In STEP 4, everyone took semaglutide for 20 weeks and lost an average of about 10.6% of their weight. Then some were switched to placebo without knowing it. Over the next 48 weeks, those who stopped regained 6.9% of their body weight, while those who continued lost another 7.9%, for a total loss of 17.4% versus 5.0%.9

The STEP 1 extension found the same pattern: one year after stopping semaglutide and the lifestyle program, people had regained about two-thirds of the weight they lost, and improvements in blood pressure, blood sugar, and cholesterol drifted back toward where they started.8

What happens when semaglutide is stopped, STEP 4After 20 weeks everyone had lost about 10.6 percent. People who continued reached 17.4 percent total loss at week 68; those switched to placebo regained weight and ended at 5.0 percent.Staying on it vs. stoppingSTEP 4: average total weight change from the start of the study0%−5%−10%−15%−20%Everyone on itWeek 0Week 20Week 68−10.6%−17.4%kept taking it−5.0%switched toplaceboAverages at the three reported time points; lines connect them. Source: Rubino et al., JAMA 2021.
Weight loss was largely maintained only when treatment continued.9

This doesn't mean you can never stop. It means obesity behaves like a chronic condition, and any plan to stop should be made with your prescriber, with a strategy for nutrition, activity, and follow-up.

Side effects and safety

Common side effects

Most side effects involve digestion: nausea, diarrhea, vomiting, constipation, stomach pain, burping, and heartburn. They are usually mild to moderate and most common when starting or raising the dose. That's why the Wegovy injection starts at 0.25 mg weekly and steps up every four weeks to the 2.4 mg maintenance dose.1 At the new 7.2 mg dose, about 22% of people in the trial reported unusual skin sensations such as tingling or sensitivity, compared with 6% on 2.4 mg.20

Serious risks to know about

  • Thyroid tumors (boxed warning). Semaglutide caused thyroid C-cell tumors in rodents; whether it does in humans is unknown. Don't use it if you or a family member has had medullary thyroid cancer, or if you have MEN 2 syndrome. Report a neck lump, hoarseness, trouble swallowing, or shortness of breath.1
  • Pancreatitis and gallbladder problems. Seek care for severe stomach pain that won't go away, pain in the upper right belly, fever, or yellowing skin.
  • Dehydration and kidney injury from ongoing vomiting or diarrhea.
  • Low blood sugar when combined with insulin or sulfonylureas.
  • Diabetic eye disease. People with type 2 diabetes and existing retinopathy should have their eyes monitored, especially when blood sugar drops quickly.
  • Sudden vision loss (NAION). Studies disagree on whether semaglutide raises the risk of this rare optic-nerve condition, but European regulators now list it as a very rare side effect.23 Get care right away for any sudden change in vision.
  • Mood changes. As with other weight-management medicines, the Wegovy label advises watching for depression or suicidal thoughts. In SELECT, psychiatric problems were no more common with semaglutide than placebo.11
  • Pregnancy. Weight loss isn't recommended during pregnancy. Because semaglutide stays in the body so long, the label advises stopping at least two months before a planned pregnancy.1
  • Surgery and anesthesia. Because it slows stomach emptying, tell your surgical team you take it before any procedure that involves sedation.

Key dates

  1. December 2017 · FDA approves Ozempic for type 2 diabetes
  2. September 2019 · Rybelsus becomes the first GLP-1 pill24
  3. June 2021 · FDA approves Wegovy for chronic weight management2
  4. March 2024 · Wegovy approved to lower cardiovascular risk, based on SELECT
  5. January 2025 · Ozempic approved for kidney protection in type 2 diabetes, based on FLOW3
  6. August 2025 · Wegovy gets accelerated approval for MASH17
  7. December 2025 · The Wegovy pill becomes the first oral GLP-1 approved for weight management24
  8. March 2026 · Wegovy HD (7.2 mg) approved20

Questions to ask your provider

  • Am I a candidate based on my weight, health conditions, and goals?
  • Does my personal or family history rule it out, such as thyroid cancer, MEN 2, or pancreatitis?
  • Would the injection or the pill fit my routine better?
  • How will we handle side effects and dose increases?
  • How should I adjust protein intake and exercise to protect muscle?
  • What is the long-term plan, including whether and how I would ever stop?

The bottom line

Semaglutide is one of the most thoroughly studied medicines in modern metabolic care. By copying a single gut hormone and making it last a week, it reduces appetite, improves blood sugar, and produces meaningful weight loss. Its outcome trials go further than most: fewer heart attacks and strokes, slower kidney decline, and healthier livers. It also has real side effects, works best as a long-term treatment, and should be used under the care of a qualified prescriber.

References

  1. Novo Nordisk. Wegovy (semaglutide) injection and tablets prescribing information. U.S. FDA; 2026. accessdata.fda.gov
  2. Wegovy (semaglutide) FDA approval history. Drugs.com. May 2026. drugs.com
  3. GLP-1 medication list 2026: FDA-approved indications, including Ozempic cardiovascular and kidney approvals. WeightLossRankings. weightlossrankings.org
  4. Editorial: Reviews and novel clinical perspectives on semaglutide, a GLP-1 receptor agonist with both injectable and oral formulations. Frontiers in Endocrinology. ncbi.nlm.nih.gov
  5. Semaglutide: an overview. ScienceDirect Topics, Elsevier. sciencedirect.com
  6. Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384(11):989–1002. pubmed.ncbi.nlm.nih.gov
  7. Impact of semaglutide on body composition in adults with overweight or obesity: STEP 1 DXA substudy. pmc.ncbi.nlm.nih.gov
  8. Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab. 2022. pubmed.ncbi.nlm.nih.gov
  9. Rubino D, et al. Effect of continued weekly subcutaneous semaglutide vs placebo on weight loss maintenance (STEP 4). JAMA. 2021;325(14):1414–1425. pubmed.ncbi.nlm.nih.gov
  10. Lincoff AM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med. 2023;389(24). nejm.org
  11. Full SELECT results affirm CV risk reduction with semaglutide in nondiabetics. TCTMD. tctmd.com
  12. Ryan DH, et al. Long-term weight loss effects of semaglutide in obesity without diabetes in the SELECT trial. Nature Medicine. 2024. nature.com
  13. SELECT trial analysis shows semaglutide's heart benefits extend beyond weight loss. Metabolic Care Today. October 2025. docwirenews.com
  14. Colhoun HM, et al. Long-term kidney outcomes of semaglutide in obesity and cardiovascular disease in the SELECT trial. Nature Medicine. 2024. ncbi.nlm.nih.gov
  15. Perkovic V, et al. Effects of semaglutide on chronic kidney disease in patients with type 2 diabetes (FLOW). N Engl J Med. 2024;391(2):109–121. pubmed.ncbi.nlm.nih.gov
  16. The FLOW study: effects of semaglutide on chronic kidney disease in patients with type 2 diabetes. International Society of Nephrology. theisn.org
  17. Novo Nordisk. Wegovy approved in the US for noncirrhotic MASH with moderate to advanced fibrosis. August 15, 2025. novonordisk.com
  18. AASLD releases updated practice guidance on semaglutide (Wegovy) for MASH. HCPLive. July 2026. hcplive.com
  19. Kosiborod MN, et al. Semaglutide in patients with heart failure with preserved ejection fraction and obesity (STEP-HFpEF). N Engl J Med. 2023;389(12):1069–1084. pubmed.ncbi.nlm.nih.gov
  20. FDA approves higher-dose semaglutide (Wegovy HD) injection 7.2 mg for obesity. HCPLive. 2026. hcplive.com
  21. Tirzepatide demonstrates superior weight loss to semaglutide in SURMOUNT-5. Applied Clinical Trials. 2026. appliedclinicaltrialsonline.com
  22. CTAD presentation lays out insights into disappointing phase 3 EVOKE trials of semaglutide in Alzheimer disease. NeurologyLive. 2026. neurologylive.com
  23. Can Ozempic and Wegovy cause blindness? Drugs.com. February 2026. drugs.com
  24. Oral semaglutide wins cardiovascular approval, followed by first-ever weight management indication. MedCentral. December 2025. medcentral.com

This article is for general education and is not medical advice. Semaglutide is a prescription medicine; talk with a licensed healthcare provider about whether it is right for you. Information is current as of September 2026 and may change as new research and FDA decisions are published. Diagrams are original illustrations by Peptide Advocate.