semaglutide

Ozempic (semaglutide injectable, 0.5–2 mg) is FDA-approved for:

• Type 2 diabetes mellitus — as an adjunct to diet and exercise to improve glycemic control in adults
• Cardiovascular risk reduction — to reduce the risk of major adverse cardiovascular events (MACE: cardiovascular death, non-fatal myocardial infarction, non-fatal stroke) in adults with type 2 diabetes and established cardiovascular disease

Wegovy (semaglutide injectable, 2.4 mg) is FDA-approved for:

• Chronic weight management in adults with initial BMI ≥30 kg/m² (obesity), or ≥27 kg/m² (overweight) with at least one weight-related comorbidity, used as an adjunct to a reduced-calorie diet and increased physical activity
• Cardiovascular risk reduction — to reduce the risk of cardiovascular death, non-fatal MI, and non-fatal stroke in adults with established cardiovascular disease and obesity or overweight (SELECT trial, 2024)

Rybelsus (semaglutide oral, 3–14 mg) is FDA-approved for:

• Type 2 diabetes mellitus — as an adjunct to diet and exercise to improve glycemic control in adults

Off-label uses (not FDA-approved but clinically practiced):

• Ozempic prescribed off-label for weight loss in patients without type 2 diabetes
• Potential benefit in non-alcoholic steatohepatitis (NASH) — under clinical investigation

Semaglutide is not approved for type 1 diabetes, diabetic ketoacidosis, or as a first-line treatment for obesity in patients without the qualifying comorbidities listed above.

Ozempic (injectable, type 2 diabetes & cardiovascular risk)

Starting dose: 0.25 mg subcutaneously once weekly for 4 weeks (initiation dose — not intended for glycemic control).

Maximum dose (Ozempic): 2 mg once weekly

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Wegovy (injectable, weight management)

Starting dose: 0.25 mg subcutaneously once weekly for 4 weeks.

Maximum dose (Wegovy): 2.4 mg once weekly. If the 2.4 mg dose is not tolerated, a temporary dose reduction to 1.7 mg may be considered for 4 additional weeks.

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Rybelsus (oral tablet, type 2 diabetes)

Starting dose: 3 mg orally once daily for 30 days (initiation dose — not intended for glycemic control).

Maximum dose (Rybelsus): 14 mg once daily.

Critical administration instruction for Rybelsus: Take on an empty stomach with up to 4 oz (120 mL) of plain water only. Wait at least 30 minutes before eating, drinking anything other than water, or taking other oral medications. Taking with food, beverages other than water, or other medications reduces absorption by up to 50%.

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General administration (injectable forms):

• Inject subcutaneously in the abdomen, thigh, or upper arm; rotate injection sites
• Administer once weekly on the same day each week, at any time of day, with or without food
• If a dose is missed: administer as soon as possible within 5 days. If more than 5 days have passed, skip and resume the regular schedule
• Storage: Refrigerate at 36°F–46°F (2°C–8°C). After first use, may store at room temperature (up to 86°F/30°C) for up to 56 days. Do not freeze. Protect from light.

Semaglutide is a GLP-1 receptor agonist — it selectively binds to and activates the GLP-1 receptor, mimicking the effects of the endogenous hormone GLP-1 that is released from intestinal L-cells after eating.

GLP-1 receptor activation produces:

• Glucose-dependent insulin secretion — stimulates first- and second-phase insulin release from pancreatic beta cells only when blood glucose is elevated, reducing the risk of hypoglycemia
• Glucagon suppression — inhibits glucagon secretion from pancreatic alpha cells in a glucose-dependent manner, reducing hepatic glucose output
• Delayed gastric emptying — slows the rate at which food leaves the stomach, blunting post-meal glucose spikes and contributing to satiety
• Central appetite suppression — acts on GLP-1 receptors in the hypothalamus and brainstem to reduce hunger signals and food intake, driving the significant weight loss seen at higher doses
• Cardiovascular benefits — direct GLP-1 receptor activation in the heart and vasculature reduces inflammation, improves endothelial function, and lowers cardiovascular event rates independent of glucose control (demonstrated in SUSTAIN-6 and SELECT trials)

Structural features enabling once-weekly dosing: Semaglutide has a plasma half-life of approximately 1 week (168 hours), achieved through two modifications: (1) a C18 fatty diacid chain attached via a linker that enables reversible albumin binding, protecting it from renal clearance; and (2) a substitution of alanine with alpha-aminoisobutyric acid at position 8, which prevents degradation by the DPP-4 enzyme. These changes extend the half-life from the 2-minute half-life of native GLP-1 to approximately 7 days.

Comparison with tirzepatide: Unlike tirzepatide, which activates both GLP-1 and GIP receptors, semaglutide activates only the GLP-1 receptor. This explains why tirzepatide produces greater average weight loss (20.2% vs. 13.7% at 72 weeks in SURMOUNT-5, NEJM 2025), though semaglutide has a longer clinical track record and more cardiovascular outcomes data.

Semaglutide does not inhibit or induce cytochrome P450 enzymes and is not a substrate of CYP enzymes, so direct pharmacokinetic drug interactions via CYP pathways are not expected.

Clinically significant interactions:

Insulin and insulin secretagogues (sulfonylureas, meglitinides): Concomitant use increases the risk of hypoglycemia. Consider reducing the dose of insulin or the secretagogue when initiating semaglutide. Monitor blood glucose closely.

Oral medications with narrow therapeutic index: Semaglutide slows gastric emptying, which can affect the rate (but generally not the extent) of absorption of orally administered drugs. Use caution with drugs that require rapid GI absorption. For oral contraceptives, consider using a non-oral method or adding a barrier method for 4 weeks after initiating semaglutide and for 4 weeks after each dose escalation.

Warfarin and other oral anticoagulants: Slowed gastric emptying may alter warfarin absorption. Monitor INR closely when initiating or adjusting semaglutide dose.

Rybelsus-specific interaction: Because oral semaglutide must be taken on an empty stomach, any other oral medication taken within 30 minutes of Rybelsus may have altered absorption. This is particularly relevant for levothyroxine, bisphosphonates, and other medications with strict fasting requirements.

No significant interactions expected with: metformin, DPP-4 inhibitors, SGLT-2 inhibitors, statins, ACE inhibitors, ARBs, or beta-blockers.

Pregnancy: Semaglutide is not recommended during pregnancy. Discontinue at least 2 months before a planned pregnancy. Animal studies showed adverse effects on fetal development. If a patient becomes pregnant while taking semaglutide, discontinue immediately and contact the prescriber.

Lactation: It is not known whether semaglutide is excreted in human breast milk. Because of the potential for serious adverse reactions in nursing infants, advise patients not to breastfeed during treatment.

Pediatric patients: Wegovy is FDA-approved for adolescents aged 12 years and older with obesity (BMI ≥95th percentile for age and sex). The dosing escalation schedule is the same as adults; the maintenance dose is 2.4 mg once weekly. Ozempic and Rybelsus are not approved for pediatric use.

Geriatric patients (≥65 years): No dose adjustment is required. Clinical trials included patients up to 80 years of age. Older patients may be more susceptible to dehydration from GI adverse reactions; monitor renal function.

Renal impairment: No dose adjustment required for any degree of renal impairment. Monitor for dehydration-related acute kidney injury.

Hepatic impairment: No dose adjustment required for mild, moderate, or severe hepatic impairment.