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Semaglutide: The Weekly GLP-1 That Redefined Obesity Care

FDA-approved GLP-1 receptor agonist marketed as Ozempic, Wegovy and Rybelsus. ~15% mean weight loss in adults with obesity at 68 weeks.

✅ Approved

Full name
Semaglutide
Class
Long-acting GLP-1 receptor agonist
Half-life
~7 days (albumin-bound)
Route
Subcutaneous weekly; oral daily (Rybelsus with SNAC absorption enhancer)
Brand names
Ozempic, Wegovy, Rybelsus (Novo Nordisk)
Regulatory status
FDA-approved — Ozempic 2017 (T2D), Rybelsus 2019 (oral T2D), Wegovy 2021 (obesity); CV risk reduction (SELECT) 2024; noncirrhotic MASH with F2–F3 fibrosis August 2025; oral Wegovy for obesity 2025 (first oral GLP-1 for weight loss).

What it is

Semaglutide is a long-acting glucagon-like peptide-1 (GLP-1) receptor agonist with 94% sequence homology to native human GLP-1. A C18 fatty-acid side chain attached via a glutamic-acid linker lets the molecule bind reversibly to plasma albumin, which shields it from the DPP-4 enzyme and extends its half-life to roughly one week — allowing once-weekly subcutaneous dosing. An oral formulation (Rybelsus) uses the absorption enhancer SNAC to shuttle intact peptide across the gastric mucosa. Semaglutide is the single-agent GLP-1 against which every newer incretin therapy is now benchmarked.

How it works

At the cellular level, semaglutide binds the GLP-1 receptor on pancreatic β-cells and potentiates glucose-dependent insulin secretion, suppresses glucagon from α-cells, and slows gastric emptying — the classic incretin triad. These peripheral effects account for its glycaemic benefit in type 2 diabetes.

For body-weight effects the central nervous system is the key site of action. GLP-1 receptors in the arcuate nucleus of the hypothalamus and in the area postrema/NTS of the brainstem respond to semaglutide by increasing anorexigenic POMC/CART neuron activity and dampening orexigenic NPY/AgRP signalling. The result is reduced hunger, increased satiety, and decreased food reward — a central anorexia that, combined with slowed gastric emptying, drives 10–15 kg mean weight loss over a year of treatment in people with obesity.

What the research shows

The STEP and SUSTAIN programmes generated one of the largest and most consistent evidence bases in modern cardiometabolic medicine — tens of thousands of participants across randomised trials in obesity, type 2 diabetes, cardiovascular prevention and organ-protection indications.

Wilding JPH et al. (2021) — STEP 1: weekly semaglutide 2.4 mg for obesity

Wilding J.P.H. et al., NEJM 2021;384:989–1002. 👥 Human studies

STEP 1 randomised 1,961 adults with obesity (mean BMI 37.9, no diabetes) to weekly subcutaneous semaglutide 2.4 mg or placebo for 68 weeks, both combined with lifestyle intervention. The primary endpoints were percent change in body weight and ≥5% weight loss at 68 weeks.

Semaglutide produced a mean weight change of −14.9% versus −2.4% for placebo. Eighty-six percent of semaglutide-treated participants lost ≥5% of body weight, 69% lost ≥10%, and 50% lost ≥15%. Cardiometabolic risk factors — waist circumference, blood pressure, HbA1c, lipids and CRP — improved in parallel.

Limitations: Gastrointestinal adverse events (nausea, diarrhoea, constipation, vomiting) were frequent and were the leading cause of the 7% treatment-discontinuation rate. Weight regain after discontinuation was not assessed in this trial but has been documented in follow-up studies.

Lincoff AM et al. (2023) — SELECT: cardiovascular outcomes in obesity without diabetes

Lincoff A.M. et al., NEJM 2023;389:2221–2232. 👥 Human studies

SELECT enrolled 17,604 adults aged ≥45 with BMI ≥27 and established cardiovascular disease but no diabetes, randomised to weekly semaglutide 2.4 mg or placebo and followed for a mean 39.8 months. The primary composite outcome was cardiovascular death, non-fatal myocardial infarction or non-fatal stroke.

Semaglutide reduced the primary endpoint by 20% (6.5% vs 8.0%; HR 0.80, 95% CI 0.72–0.90, p<0.001). Benefits emerged within the first year and persisted throughout follow-up. The trial established that weight-directed GLP-1 therapy produces cardiovascular benefit in people with obesity independent of diabetes status.

Limitations: The trial enrolled a high-risk secondary-prevention population; applicability to primary prevention is not proven. The mechanism of benefit — direct vascular effect versus weight-mediated effect — remains under analysis.

Rubino D et al. (2021/2022) — STEP 4 and STEP 5: durability of effect

Rubino D. et al., JAMA 2021;325:1414–25; Garvey WT et al., Nat Med 2022;28:2083–91. 👥 Human studies

STEP 4 tested what happens when treatment is continued versus withdrawn: after 20 weeks of open-label semaglutide run-in, 803 participants were randomised to continue 2.4 mg weekly or switch to placebo. Continuation produced a further −7.9% weight loss; withdrawal produced +6.9% weight regain.

STEP 5 extended treatment to 104 weeks in 304 participants, demonstrating a sustained mean weight loss of −15.2% on semaglutide versus −2.6% on placebo. Together these trials establish that semaglutide-induced weight loss requires continued therapy and is partly reversible on discontinuation.

Limitations: Long-term data beyond two years remain limited. Real-world discontinuation rates are higher than in trials owing to cost, supply and GI tolerance.

Safety and limitations

Gastrointestinal adverse effects dominate the safety profile and are most common during dose escalation: nausea (44%), diarrhoea (32%), constipation (24%) and vomiting (25%). Slow titration over 16 weeks and dose pauses reduce but do not eliminate these symptoms.

Rare but serious signals include pancreatitis, gallbladder disease (with accelerated stone formation during rapid weight loss) and a class-wide boxed warning for thyroid C-cell tumours based on rodent findings. Semaglutide is contraindicated in personal or family history of medullary thyroid carcinoma and in multiple endocrine neoplasia syndrome type 2. Diabetic retinopathy complications have been noted when HbA1c falls rapidly in long-standing T2D. Muscle-mass loss (~25–40% of total weight lost) is a recognised concern with high-efficacy GLP-1s.

Sources

  1. Wilding J.P.H. et al. "Once-weekly semaglutide in adults with overweight or obesity." NEJM 2021;384:989–1002. PubMed
  2. Lincoff A.M. et al. "Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT)." NEJM 2023;389:2221–2232. PubMed
  3. Rubino D. et al. "Effect of continued weekly subcutaneous semaglutide vs placebo on weight loss maintenance (STEP 4)." JAMA 2021;325:1414–1425. PubMed
  4. Garvey W.T. et al. "Two-year effects of semaglutide in adults with overweight or obesity: the STEP 5 trial." Nat Med 2022;28:2083–2091. PubMed
  5. Marso S.P. et al. "Semaglutide and cardiovascular outcomes in patients with type 2 diabetes (SUSTAIN-6)." NEJM 2016;375:1834–1844. PubMed
  6. Husain M. et al. "Oral semaglutide and cardiovascular outcomes in patients with type 2 diabetes (PIONEER 6)." NEJM 2019;381:841–851. PubMed

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