Semaglutide is a glucagon-like peptide-1 (GLP-1) receptor agonist, a class of medications that mimics the action of the natural hormone GLP-1 in the body. It is primarily used for the treatment of type 2 diabetes, weight management, and to reduce the risk of major cardiovascular events in certain adult patients .

Mechanism of Action

semaglutide works by activating GLP-1 receptors, which leads to several physiological effects. These include stimulating insulin production from the pancreas in a glucose-dependent manner, reducing the liver’s production of sugar, slowing down gastric emptying, and helping to control appetite and food intake . By mimicking the naturally occurring GLP-1 hormone, semaglutide helps individuals feel fuller for longer, eat less, and achieve better control over blood sugar levels, contributing to weight loss and a reduced risk of cardiovascular disease . The exact mechanism by which semaglutide reduces kidney-related risks is not yet fully understood .

FDA-Approved Versions and Uses

As of today, May 30, 2025, semaglutide is available under several FDA-approved brand names, all manufactured by Novo Nordisk :

Ozempic (injection): First approved on December 5, 2017, Ozempic is indicated for adults with type 2 diabetes to improve blood sugar control, reduce the risk of major cardiovascular events (such as heart attack, stroke, or death) in those with known heart disease, and reduce the risk of kidney function decline, kidney failure, and death due to cardiovascular disease in adults with chronic kidney disease (CKD) and type 2 diabetes. It is administered as a once-weekly subcutaneous injection .
Wegovy (injection): Approved for chronic weight management in adults and adolescents aged 12 years and older with obesity, or overweight adults with at least one weight-related comorbidity . Wegovy is also administered as a once-weekly subcutaneous injection and should be used in conjunction with a reduced-calorie diet and increased physical activity .
Rybelsus (oral tablets): This is the first oral GLP-1 receptor agonist, approved for adults with type 2 diabetes to improve blood sugar control. Rybelsus is taken once daily, at least 30 minutes before the first food, beverage, or other oral medications of the day, with no more than 4 ounces of plain water .

Administration and Dosing

The administration and dosing of semaglutide vary by brand and indication.

Ozempic and Wegovy are administered as subcutaneous injections, typically once weekly, on the same day each week, at any time of the day, with or without food. Injection sites include the stomach, thigh, or upper arm . Dosing for both medications involves a gradual escalation to minimize gastrointestinal side effects. For Ozempic, the starting dose is 0.25 mg once weekly, escalating to a maximum of 2 mg once weekly. For Wegovy, the starting dose is 0.25 mg once weekly, escalating to a maintenance dose of 2.4 mg once weekly .
Rybelsus is an oral tablet taken daily. The starting dose is 3 mg once daily for 30 days, increasing to 7 mg once daily, and potentially to 14 mg once daily if further glycemic control is needed . A newer formulation also offers 1.5 mg, 4 mg, and 9 mg doses .

Missed doses for injectable semaglutide (Ozempic, Wegovy) can typically be administered within a few days, but specific guidelines exist for when to skip a dose and resume the regular schedule . For oral Rybelsus, a missed dose should be skipped, and the next dose taken the following day.

Side Effects and Warnings

Common side effects of semaglutide often include gastrointestinal issues such as nausea, vomiting, diarrhea, constipation, abdominal pain, and indigestion . These are typically mild and tend to improve over time. Serious side effects, though less common, can include pancreatitis, gallbladder problems (e.g., gallstones), acute kidney injury, severe hypoglycemia (especially when used with other diabetes medications), and allergic reactions .

Semaglutide carries a boxed warning regarding the risk of thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), observed in animal studies . Therefore, semaglutide is contraindicated in patients with a personal or family history of MTC or in patients with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2) . Other warnings include diabetic retinopathy complications, increased heart rate (with Wegovy), and potential for suicidal behavior or ideation (with Wegovy) . Patients should discuss their full medical history with their doctor before starting semaglutide.

Concerns with Unapproved and Compounded Semaglutide

The high demand for GLP-1 drugs, particularly for weight loss, has led to the proliferation of unapproved and illegally marketed versions of semaglutide . The U.S. Food and Drug Administration (FDA) has expressed significant concerns regarding these products due to potential risks to patient safety, effectiveness, and quality

Unapproved Versions: Unlike FDA-approved drugs, unapproved versions do not undergo the rigorous review process for safety, effectiveness, and quality before being marketed. This means their contents, purity, and potency are not verified, posing significant health risks .
Compounded Drugs: Compounded drugs are custom-prepared medications by a pharmacist to meet the specific needs of an individual patient, often when an FDA-approved drug is not commercially available or cannot meet a patient’s medical need . However, compounded drugs are not FDA-approved, meaning the agency does not review them for safety, effectiveness, or quality .
- Dosing Concerns: The FDA has received numerous reports of adverse events, some requiring hospitalization, related to dosing errors with compounded injectable semaglutide and tirzepatide products . These errors can stem from patients self-administering incorrect doses or healthcare professionals miscalculating doses. Some patients have been prescribed compounded semaglutide or tirzepatide in doses exceeding what is in the FDA-approved drug label, leading to serious adverse events like severe nausea, vomiting, diarrhea, and abdominal pain
- Salt Forms: The FDA is aware that some compounded semaglutide products may use salt forms, such as semaglutide sodium or semaglutide acetate . These are different active ingredients than those used in the FDA-approved drugs, and the FDA lacks information on whether these salt forms have the same chemical and pharmacologic properties or are safe and effective .
- Underreported Adverse Events: Federal law does not require state-licensed pharmacies that are not outsourcing facilities to submit adverse events to the FDA for compounded drugs, leading to likely underreporting of issues with compounded semaglutide . As of April 30, 2025, the FDA had received 520 reports of adverse events associated with compounded semaglutide ^[3].
Illegally Marketed Versions:
- Counterfeit Products: The FDA has identified counterfeit Ozempic in the U.S. Counterfeit drugs are illegal and may contain incorrect ingredients, too little or too much active ingredient, or harmful substances ^[3].
- Online Sales: Illegally marketed semaglutide and tirzepatide are sold online, often by entities not operating as state-licensed pharmacies ^[3]. These products may be counterfeit, contain wrong or harmful ingredients, or have incorrect active ingredient amounts ^[3].
- “For Research Purposes” or “Not for Human Consumption”: Some companies illegally sell unapproved semaglutide, tirzepatide, or retatrutide products falsely labeled “for research purposes” or “not for human consumption,” but market them directly to consumers with dosing instructions ^[3]. These products are of unknown quality and may be harmful ^[3]. Retatrutide, specifically, cannot be used in compounding under federal law as it is not a component of an FDA-approved drug and has not been found safe and effective for any condition ^[3].

FDA Recommendations for Patients

The FDA strongly advises patients to obtain prescriptions for semaglutide from their doctor and fill them at state-licensed pharmacies ^[3]. Patients should also utilize resources like the FDA’s BeSafeRx campaign for guidance on safely purchasing prescription medicines online ^[3]. Any questions or concerns about medications should be discussed with a healthcare provider ^[3].

Reporting Issues to FDA

Healthcare professionals, patients, and compounders are encouraged to report any adverse events or quality problems related to semaglutide or any other medication to the FDA’s MedWatch Adverse Event Reporting program ^[3]. This can be done online or by submitting a downloaded form via fax