Semaglutide

Semaglutide is a synthetic GLP-1 receptor agonist developed by Novo Nordisk. It is a 31-amino-acid peptide with a fatty acid chain that binds albumin, extending the half-life to approximately one week. It is sold as Ozempic (type 2 diabetes injection), Wegovy (obesity injection), and Rybelsus (oral type 2 diabetes tablet).

The molecule was approved by the FDA in December 2017 as Ozempic for adults with type 2 diabetes. The oral formulation Rybelsus was approved in September 2019, making semaglutide the first orally bioavailable GLP-1 agonist. Wegovy followed in June 2021 for chronic weight management. The cardiovascular indication was added to Wegovy in March 2024 after the SELECT readout. The chronic kidney disease label expansion in type 2 diabetes followed the FLOW trial published in NEJM in 2024.

The Diabetes Evidence: SUSTAIN

The SUSTAIN program established semaglutide for type 2 diabetes. SUSTAIN-6 (Marso et al., NEJM, 2016) was the cardiovascular safety trial that the FDA required for the original approval. In 3,297 patients with type 2 diabetes and high cardiovascular risk, semaglutide reduced major adverse cardiovascular events by 26 percent over 2 years versus placebo. This was the first GLP-1 cardiovascular outcomes trial to show clear benefit.

SUSTAIN-7 compared subcutaneous semaglutide head-to-head with dulaglutide. Semaglutide produced superior A1C reduction and weight loss across both doses tested. The SOUL trial (oral semaglutide cardiovascular outcomes, published in NEJM in 2025) extended cardiovascular benefit to the oral formulation in high-risk type 2 diabetes.

The Obesity Evidence: STEP

The STEP program tested injectable semaglutide 2.4 mg weekly in adults with obesity, with or without comorbidities. STEP-1 (Wilding et al., NEJM, 2021) randomized 1,961 adults to semaglutide or placebo for 68 weeks. Mean weight loss was 14.9 percent with semaglutide versus 2.4 percent with placebo. STEP-2 in adults with type 2 diabetes reported lower weight loss in the diabetic population (a recurring pattern across incretin trials).

STEP-4 was the maintenance trial. Patients who completed a 20-week lead-in were randomized to continue semaglutide or switch to placebo for 48 weeks. The placebo group regained an average of 6.9 percent of body weight. The semaglutide group continued to lose. The trial established the same durability pattern seen with tirzepatide: the drug works while you take it.

The most recent STEP trial is STEP UP, which tested a higher 7.2 mg weekly dose versus the standard 2.4 mg. Announced by Novo Nordisk in January 2025, STEP UP reported 20.7 percent mean weight loss at 7.2 mg over 68 weeks versus the standard dose, with 33 percent of patients achieving 25 percent or greater weight loss. STEP UP brings semaglutide closer to tirzepatide in efficacy, though the head-to-head SURMOUNT-5 trial still favored tirzepatide at labeled doses.

SELECT: The Cardiovascular Outcomes Trial

SELECT (Lincoff et al., NEJM, 2023) is the cardiovascular outcomes trial that changed how semaglutide is prescribed. The trial randomized 17,604 adults aged 45 or older with a BMI of at least 27 and established cardiovascular disease but without diabetes to semaglutide 2.4 mg weekly or placebo. The primary endpoint was a composite of cardiovascular death, non-fatal myocardial infarction, or non-fatal stroke.

After a median follow-up of 39.8 months, semaglutide reduced the primary endpoint by 20 percent (hazard ratio 0.80, 95% CI 0.72 to 0.90, p < 0.001). The Kaplan-Meier curves separated early and stayed separated, suggesting both early and sustained benefit. The trial led to the March 2024 FDA label expansion adding cardiovascular risk reduction to the Wegovy indication.

A 2025 prespecified analysis published in The Lancet (Deanfield et al., 2025) examined whether the cardiovascular benefit tracked with weight loss. It did not. The cardioprotective effect appeared largely independent of baseline adiposity and the magnitude of weight reduction, with waist circumference change accounting for only about 33 percent of the observed effect in mediation analysis. The authors argued that GLP-1 agonists should be reconceptualized as disease-modifying cardiovascular drugs rather than tools for weight management alone.

Long-term weight-loss data from SELECT (Ryan et al., Nature Medicine, 2024) reported sustained 10.2 percent mean weight reduction at 208 weeks (4 years) versus 1.5 percent for placebo. Weight loss continued through 65 weeks and was maintained thereafter, which is the longest published follow-up for any GLP-1 in obesity.

Semaglutide binds the GLP-1 receptor, a G-protein-coupled receptor expressed in pancreatic beta cells, the hypothalamus, the area postrema (brainstem nausea center), and several peripheral tissues. The structural modifications compared with native GLP-1 are what make the drug a useful therapy rather than a curiosity.

Native GLP-1 has a half-life of about 1 to 2 minutes due to rapid degradation by dipeptidyl peptidase IV (DPP-IV). Semaglutide carries two substitutions at positions 8 and 34 plus an attached C18 fatty acid that binds plasma albumin. The combination produces a half-life of approximately 165 hours (around 7 days) and allows once-weekly subcutaneous dosing.

In the pancreas, semaglutide stimulates glucose-dependent insulin release. The glucose-dependent feature matters: insulin is only released when blood glucose is increased, which prevents hypoglycemia in patients without other glucose-lowering drugs. In the brainstem and hypothalamus, GLP-1 receptor activation reduces appetite and slows gastric emptying. The appetite effect is what drives the weight-loss outcomes seen in the STEP and SELECT programs. Cardioprotection appears to involve direct vascular effects, blood pressure reduction, and reduced systemic inflammation, mechanisms that are still being characterized in mechanistic substudies.

Type 2 Diabetes Outcomes

In SUSTAIN trial pooled data, semaglutide at the 1 mg weekly dose produced mean A1C reduction of 1.5 to 1.8 percentage points from baseline over 30 to 56 weeks, with concurrent fasting plasma glucose reduction of 30 to 50 mg/dL and mean weight loss of 4.5 to 6.5 kg. The A1C response is larger than what older GLP-1 agonists (exenatide, liraglutide) produced and is the basis for the head-to-head superiority of semaglutide in SUSTAIN-7 versus dulaglutide. Real-world A1C reductions tend to be smaller than trial figures because patient adherence in clinical practice is lower than in supervised trials.

The oral Rybelsus formulation produces somewhat smaller effects than the injectable. The PIONEER program reported A1C reduction of 1.0 to 1.4 percentage points at the 14 mg maximum oral dose. The lower potency reflects the limited oral bioavailability of GLP-1 peptides, even with the SNAC absorption enhancer used in Rybelsus.

Obesity Outcomes

The STEP program data spans the full range of obesity treatment.

STEP-1 (no diabetes): 14.9 percent mean weight loss at 2.4 mg over 68 weeks, with 32 percent of patients achieving 20 percent or greater weight loss and 50 percent achieving 15 percent or greater.

STEP-2 (with type 2 diabetes): 9.6 percent mean weight loss. The diabetic population consistently loses less weight on GLP-1 agonists than the non-diabetic population, an unexplained pattern that recurs across the entire incretin class.

STEP-4 (maintenance): Patients who continued semaglutide after a 20-week lead-in continued to lose weight through 68 weeks. The placebo-crossover group regained 6.9 percent. The drug must be continued for weight loss to be sustained.

STEP-5 (long-term, 104 weeks): 15.2 percent mean weight loss versus 2.6 percent for placebo. The 2-year data showed weight loss largely plateaued by week 60 and was maintained thereafter.

STEP UP (7.2 mg high dose, 2025): 20.7 percent mean weight loss with 33 percent of patients achieving 25 percent or greater weight loss over 68 weeks. The 7.2 mg dose is awaiting FDA submission and has not yet been added to the Wegovy label.

Body composition changes track total weight loss. Approximately 40 percent of weight lost on semaglutide is fat-free mass (muscle, bone, water, organs), which is consistent with other obesity interventions. This proportion has driven the conversation about combining semaglutide with resistance training to preserve lean mass.

Cardiovascular Outcomes

The SELECT trial outcomes have been described in detail in the research summary. Three additional points are worth noting here.

First, the cardiovascular benefit in SELECT was driven primarily by reduced non-fatal myocardial infarction (28 percent reduction) and cardiovascular death (15 percent reduction). Stroke reduction was smaller and not individually statistically significant. The composite outcome was driven by MI and CV death.

Second, the benefit emerged early. The Kaplan-Meier curves separated within the first year, before most weight loss had occurred. This early divergence is consistent with the 2025 Lancet mediation analysis suggesting weight-loss-independent mechanisms.

Third, secondary outcomes included heart failure with preserved ejection fraction (HFpEF). STEP-HFpEF, a separate trial of 263 patients with HFpEF and obesity, reported improved Kansas City Cardiomyopathy Questionnaire scores and 6-minute walk distance with semaglutide. The HFpEF indication was added to the Wegovy label in 2024.

Chronic Kidney Disease Outcomes

The FLOW trial in adults with type 2 diabetes and chronic kidney disease reported a 24 percent reduction in major kidney events (kidney failure, sustained 50 percent decline in eGFR, or kidney or cardiovascular death) over a median 3.4 years. The benefit emerged within the first year and persisted throughout follow-up. The CKD label expansion in 2024 made semaglutide one of the few diabetes drugs with formal renal protection labeling alongside SGLT2 inhibitors.

Off-Label and User-Reported Effects

Beyond approved indications, patient and clinician reports describe several off-label effect patterns.

Reduced food cravings and "food noise." This is the most commonly reported subjective change. Patients describe the loss of constant thoughts about food, particularly cravings for sweets, salty snacks, and alcohol. Reduced alcohol intake has been formally observed in retrospective cohort studies. A small randomized trial in alcohol use disorder is ongoing.

Reduced compulsive behaviors. Anecdotal reports describe reduced gambling, shopping, and other compulsive behaviors. These effects have not been characterized in controlled trials and remain hypothesis-generating observations rather than established outcomes.

"Ozempic face" and skin changes. Rapid weight loss produces visible loss of facial fat. The effect is mechanically expected with any rapid weight loss intervention and is not unique to semaglutide. It is reversible if weight is regained or if hyaluronic acid fillers are used to restore facial volume.

Hair shedding. Reported in 3 to 4 percent of obesity-trial patients versus 1 to 2 percent of placebo patients. Mechanistically consistent with telogen effluvium from rapid weight loss rather than a direct drug effect. Generally reversible after weight stabilization.

Fatigue and reduced energy. Reported during the dose-escalation phase and during periods of reduced caloric intake. The effect typically resolves with continued treatment as the body adjusts to the lower caloric intake.

None of the off-label effects has the trial-grade evidence backing of the approved indications.

Approved Label Doses

The FDA-approved dose protocols differ across the three semaglutide products.

Ozempic (type 2 diabetes, subcutaneous injection): Start at 0.25 mg once weekly for 4 weeks (a starter dose not intended for glycemic effect, used solely to limit gastrointestinal side effects). Increase to 0.5 mg weekly for at least 4 weeks. The maintenance dose is 0.5, 1.0, or 2.0 mg weekly depending on glycemic response. Maximum approved dose for type 2 diabetes is 2.0 mg weekly.

Wegovy (obesity, subcutaneous injection): Start at 0.25 mg weekly and escalate every 4 weeks through 0.5 mg, 1.0 mg, and 1.7 mg to reach the maintenance dose of 2.4 mg once weekly by week 16. The new 7.2 mg weekly dose from the STEP UP trial has been announced but is not yet on the Wegovy label as of mid-2026. Awaiting FDA submission and review.

Rybelsus (oral type 2 diabetes): Start at 3 mg once daily for 30 days (a tolerance-building starter dose). Increase to 7 mg once daily. If additional glycemic control is needed after 30 days at 7 mg, increase to 14 mg once daily. Maximum approved oral dose is 14 mg daily. Rybelsus must be taken at least 30 minutes before the first food, beverage, or other oral medication of the day with no more than 4 ounces of water, because the SNAC absorption enhancer requires an empty stomach to function.

Cardiovascular and renal indications: Use the dose for the underlying condition (T2D or obesity). The CV indication in Wegovy uses 2.4 mg weekly. The CV indication in Ozempic uses the established type 2 diabetes dose. The CKD indication uses the type 2 diabetes Ozempic dose.

Dose Titration Rationale

The slow upward titration across 16 weeks for Wegovy and across at least 8 weeks for Ozempic is driven by gastrointestinal tolerance, not by pharmacokinetic considerations. Starting at the target dose would produce intolerable nausea, vomiting, and diarrhea in most patients. The titration allows the gastrointestinal system to adapt. About 7 percent of patients still discontinue due to side effects despite the titration schedule.

Pharmacokinetics

Semaglutide has an apparent terminal elimination half-life of approximately 165 hours, or roughly 7 days. Steady-state plasma concentrations are reached after 4 to 5 weekly doses (about a month). Peak concentrations occur 1 to 3 days after each subcutaneous injection. The long half-life is what allows once-weekly dosing. It also means dose changes take a month to fully take effect, and side effects can persist for weeks after discontinuation.

The injectable formulation is administered subcutaneously in the abdomen, thigh, or upper arm. Injection site rotation is recommended but the site does not meaningfully affect absorption. Oral Rybelsus has bioavailability of approximately 1 percent (compared with ~100 percent for the injectable), which is enabled by the SNAC absorption enhancer.

The molecule is metabolized through proteolytic cleavage and beta-oxidation of the fatty acid side chain. Renal and hepatic impairment do not produce clinically meaningful changes in semaglutide pharmacokinetics in published dose-finding studies, so no dose adjustment is required in mild to moderate organ impairment.

Unit Conversion (Compounded Products)

The labeled semaglutide products are dosed in milligrams. Compounded semaglutide (now no longer legally available, see below) was often dosed in "units" using insulin syringes. The conversion depends on the concentration of the compounded product, which varied widely.

A common compounded concentration was 1 mg/mL. At that concentration, 40 units on a U-100 insulin syringe (which measures 0.4 mL) corresponds to approximately 0.4 mg of semaglutide. Compounded concentrations of 2.5 mg/mL and 5 mg/mL also circulated, with corresponding higher mg-per-unit ratios. Dosing errors during the compounded-semaglutide era were attributed in significant part to concentration confusion and unit-to-mg conversion mistakes.

Off-Label Compounded Use (No Longer Legal in US)

Compounded semaglutide was widely available through 503A and 503B pharmacies from 2022 through early 2025 under the FDA shortage provisions. The drug shortage was driven by demand outstripping Novo Nordisk supply capacity. In February 2025, the FDA removed semaglutide from the active shortage list, which terminated the legal basis for compounding the active pharmaceutical ingredient. Most compounding pharmacies stopped producing the drug between February and June 2025. The compounded-semaglutide market has largely ended in the US compounding system, although some operations continue in regulatory gray zones.

Off-label dose patterns that circulated during the compounding era included microdosing (0.1 to 0.25 mg weekly, below the standard starter dose) for appetite control without weight loss, and stop-reduce-restart cycles to maintain weight loss after target weight was reached. Neither pattern has trial-grade evidence support. The microdosing approach was particularly popular but lacks any controlled pharmacokinetic or efficacy data, and the steady-state requirement (4 to 5 weeks at any given dose) makes rapid dose adjustments problematic in any case.

The dominant adverse event is gastrointestinal. Nausea (44 percent in STEP-1), diarrhea, constipation, and vomiting are most common during dose escalation. The dose-titration schedule (0.25 mg weekly increased every 4 weeks to a target maintenance dose) is designed to limit these effects. Most events are mild to moderate and resolve with continued treatment. Discontinuation due to adverse events ran 7 percent in STEP-1 versus 3 percent in placebo.

Acute pancreatitis has been observed across the GLP-1 class at low rates and requires immediate discontinuation if suspected. Gallbladder disease (cholecystitis and cholelithiasis) occurs at modestly increased rates compared with placebo, an effect related to rapid weight loss. Acute kidney injury can develop in patients who become severely dehydrated from vomiting.

Thyroid C-cell tumors are the subject of a boxed warning based on rodent data with liraglutide (a related GLP-1 agonist). Personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia syndrome type 2 (MEN2) is a contraindication.

Reports of suicidal ideation in patients on GLP-1 agonists prompted FDA review in 2023 to 2024. The agency concluded that the available evidence did not support a causal association, and labeling was not changed. Monitoring continues.

Three molecules dominate the incretin obesity space in 2026.

Semaglutide is the established standard with the broadest clinical evidence base, the longest cardiovascular outcomes data, and the most extensive real-world experience. Wegovy weight loss at 2.4 mg is approximately 15 percent at 68 weeks. The new 7.2 mg dose (STEP UP) increases this to about 20 percent.

Tirzepatide outperformed semaglutide head-to-head in SURMOUNT-5 (20.2 percent vs 13.7 percent at 72 weeks). It has cardiovascular benefit data emerging from the SUMMIT and SURPASS-CVOT programs. The OSA indication is unique to tirzepatide in 2026.

Retatrutide is investigational. TRIUMPH-4 reported 28.7 percent mean weight loss at 12 mg over 68 weeks in obesity with knee osteoarthritis. FDA approval is projected for late 2027. Retatrutide carries a higher gastrointestinal and dysesthesia signal than the other two.

For most patients, the choice depends less on efficacy ranking and more on insurance coverage, side-effect tolerance, and the specific comorbid indication being targeted.

For informational and educational purposes only. Not medical advice. Not for human consumption unless prescribed by a licensed physician for an FDA-approved indication. Consult a qualified healthcare provider before using any peptide or pharmaceutical product.