Semaglutide

Quick summary

Semaglutide is a once-weekly subcutaneous (or once-daily oral) peptide that activates the GLP-1 receptor (glucagon-like peptide-1 receptor). It is available under three brand names: Ozempic for type 2 diabetes (subcutaneous, launched 2017), Wegovy for chronic weight management (subcutaneous 2.4 mg, launched 2021), and Rybelsus for type 2 diabetes (oral tablet, launched 2019).

In adults with type 2 diabetes the SUSTAIN program showed HbA1c reductions of approximately 1.2 to 1.8 percentage points versus placebo across the 0.5 and 1 mg doses.^[5] In adults with obesity but without diabetes the STEP-1 trial reported a mean body weight reduction of approximately 14.9 % at the 2.4 mg dose over 68 weeks.^[2] The SELECT cardiovascular outcomes trial (2023) demonstrated a 20 % relative reduction in major adverse cardiovascular events (MACE) in people with overweight or obesity and established cardiovascular disease but without diabetes.^[3]

Semaglutide has a mean terminal half-life of approximately 165 hours(about one week), supporting once-weekly dosing. It carries a boxed warning for thyroid C-cell tumors observed in rodent studies and is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN-2).^[7]

Discovery and development

Semaglutide was developed by Novo Nordisk from the earlier GLP-1 analogue liraglutide (Victoza), which had a 13-hour half-life requiring daily injection. The design objective was a molecule with a half-life long enough for once-weekly dosing, achieved primarily by switching the fatty acid conjugate attached to the peptide backbone from a C16 chain (liraglutide) to a C18 fatty diacid connected through a short linker.^[10] A substitution at position 8 of the GLP-1 sequence also protected the peptide against rapid cleavage by the enzyme DPP-4.

The subcutaneous formulation received FDA approval as Ozempic for type 2 diabetes in December 2017, followed by approval for cardiovascular risk reduction in T2DM patients with established CVD in 2020 (based on the SUSTAIN-6 trial). An oral formulation, Rybelsus, was approved in September 2019, the first oral GLP-1 receptor agonist to reach the market. The higher 2.4 mg dose was approved as Wegovy for chronic weight management in June 2021, and in March 2024 the FDA approved an additional cardiovascular risk-reduction indication for Wegovy based on the SELECT trial outcome.

Structure and design

Semaglutide is a 31 amino-acid synthetic peptide with a molecular weight of approximately 4,113 daltons. Three structural features distinguish it from native GLP-1:

• Aib substitution at position 8. An alpha-aminoisobutyric acid residue replaces alanine at position 8. This sterically blocks DPP-4 from cleaving the N-terminus of the peptide, dramatically extending in-vivo stability from a plasma half-life of minutes (native GLP-1) to days.
• Arg34 substitution. Replacement of lysine with arginine at position 34 redirects site-specific chemistry to lysine at position 26, ensuring the fatty acid linker is attached at a defined location.
• C18 fatty diacid at Lys26 via a linker. A C18 fatty diacid is attached to lysine-26 through a gamma-glutamate and two mini-PEG (OEG) spacer units. The hydrophobic chain non-covalently binds serum albumin, slowing renal filtration and extending the half-life to approximately one week.^[10]

The oral formulation (Rybelsus) adds a further challenge: peptides are not absorbed across the gastric epithelium without help. Rybelsus co-formulates semaglutide with SNAC(sodium N-(8-(2-hydroxybenzoyl)amino)caprylate), an absorption enhancer that transiently increases gastric mucosal permeability and raises local pH to protect the peptide from proteolytic degradation. Oral bioavailability with SNAC is approximately 1 %, far below the approximately 89 % achieved subcutaneously, but high enough to produce therapeutically meaningful plasma exposures at the 7 and 14 mg doses.

Mechanism of action

Semaglutide is a selective GLP-1 receptor agonist. On binding the GLP-1 receptor, it stimulates glucose-dependent insulin secretion from pancreatic beta cells, suppresses inappropriate glucagon from alpha cells, slows gastric emptying (which blunts postprandial glucose spikes), and acts on hypothalamic and brainstem circuits to reduce appetite and food intake. Together these effects lower fasting and postprandial glucose and reduce body weight. The weight loss effect is substantially driven by central appetite suppression rather than glucose-mediated calorie restriction alone.

A more detailed breakdown of receptor signaling and downstream metabolic effects is in the dedicated article: Semaglutide Mechanism of Action →

Pharmacokinetics in summary

• Subcutaneous bioavailability: approximately 89 %.^[7]
• Oral bioavailability (Rybelsus with SNAC): approximately 1 %. Highly sensitive to food; must be taken on an empty stomach with a maximum of 120 mL of plain water, 30 minutes before the first food or drink of the day.
• Time to peak (Tmax, SC): 1 to 3 days post-dose.
• Terminal half-life (t½): approximately 165 hours (about 1 week); supports once-weekly dosing with steady-state reached in 4 to 5 weeks.^[7]
• Volume of distribution at steady state (Vss): approximately 12.5 L.
• Plasma protein binding: greater than 99 %, primarily to serum albumin via the C18 fatty diacid moiety.
• Metabolism: proteolytic cleavage of the peptide backbone and beta-oxidation of the fatty acid chain. No cytochrome P450 involvement.

Full PK parameters, dose-titration schedules for all three formulations, and special-population data are in: Semaglutide Half-Life and Pharmacokinetics →

Pivotal clinical evidence

Four registered Phase III programs anchor semaglutide's evidence base: SUSTAIN (subcutaneous semaglutide in T2DM, ten trials), PIONEER (oral semaglutide in T2DM, ten trials), STEP (subcutaneous semaglutide 2.4 mg for obesity, four trials), and SELECT (cardiovascular outcomes in overweight/obesity without diabetes).

The cardiovascular benefit was first demonstrated in T2DM patients by SUSTAIN-6^[1] and later confirmed and extended to people without diabetes by SELECT.^[3] SELECT enrolled 17,604 participants, making it one of the largest cardiovascular outcomes trials in the GLP-1 RA class.

Safety overview

The most common adverse events in pivotal trials were gastrointestinal: nausea, diarrhea, vomiting, constipation, and decreased appetite. Most were mild to moderate in intensity and attenuated with continued dosing at a stable dose. The product label carries a boxed warning for thyroid C-cell tumors based on rodent studies; semaglutide is contraindicated in patients with a personal or family history of medullary thyroid carcinoma or MEN-2.^[7]

SUSTAIN-6 identified a numerically higher rate of new or worsening diabetic retinopathy complications in the semaglutide arm (3.0 % vs 1.8 % placebo), attributed provisionally to the speed of glycemic improvement in patients with established retinopathy.^[1] This signal led to a label warning for patients with diabetic retinopathy.

Detailed safety data, including frequencies for each adverse event category, pancreatitis risk, gallbladder disease, the post-marketing suicidal ideation signal, gastroparesis considerations, pregnancy, and lactation, are in: Semaglutide Safety Profile →

Approved indications and access

Regulatory status differs by formulation and indication; use the region switcher to view the agency-specific block for your jurisdiction. As of the last review date, semaglutide is approved in the United States, the European Union, the United Kingdom, Australia, and Canada for type 2 diabetes mellitus (Ozempic and Rybelsus). The 2.4 mg weight management formulation (Wegovy) is approved in all five regions, though reimbursement and access vary substantially by jurisdiction and payer. The cardiovascular risk-reduction indication based on SELECT is approved in the United States for Wegovy; regulatory review of this indication is ongoing in other regions.