Peptide Health Lab

Metabolic & GLP-1

Semaglutide

Also known as: GLP-1 receptor agonist, Ozempic, Wegovy, Rybelsus

Regulatory status
FDA approved
Evidence grade
Human RCT evidence

Last reviewed August 2, 2026 · 18 sources

What semaglutide is and how it works

Semaglutide is a synthetic analogue of glucagon-like peptide-1, a hormone released by the gut after eating. The native hormone survives only minutes in circulation; semaglutide was engineered around that problem, and its extended half-life of roughly one week is what makes once-weekly injection possible.[2]

Acting at the GLP-1 receptor produces several effects at once: glucose-dependent insulin release, suppression of glucagon, slowed gastric emptying, and reduced appetite through central pathways. The glucose dependence matters: insulin release falls away as glucose falls, which is why hypoglycemia rates in monotherapy trials are low. A review of the class describes how this pharmacology was extended first to cardiovascular and kidney outcomes and then to entirely new indications under investigation.[13]

It exists in two dosage forms. The injectable is a ready-to-use solution given subcutaneously once weekly. An oral tablet formulation also reaches meaningful exposure; it was tested at 50 mg daily in the OASIS 1 dose-finding trial,[8] and the strength that carried through to approval for weight management is the lower 25 mg daily tablet studied in OASIS 4.[18] Both require a prescription and clinician management in the United States; neither is available as a supplement, and neither should be thought of as a research peptide, because unlike most compounds in this library semaglutide has an approved manufacturer, a label, and a regulated quality standard behind it.

What the research actually shows

This is one of the largest randomized evidence bases in metabolic medicine, and that is the honest headline. SUSTAIN in diabetes, STEP in weight management, and the dedicated outcome trials cover tens of thousands of randomized participants with hard endpoints, not surrogate markers.

Weight. STEP 1 enrolled 1,961 adults with obesity and without diabetes and randomized them 2:1 to 2.4 mg weekly or placebo for 68 weeks, both alongside lifestyle intervention. Mean weight change was −14.9% versus −2.4%; 69.1% of the treated group lost at least 10% of body weight and 50.5% lost at least 15%.[3] In adults who also had type 2 diabetes, the same dose produced a smaller mean reduction of 9.6% versus 3.4% on placebo.[4] The daily oral tablet produced a 15.1% mean reduction over the same 68 weeks at the 50 mg dose-finding strength,[8] and 13.6% versus 2.2% at week 64 at the 25 mg strength that was subsequently approved.[18]

Cardiovascular outcomes. SUSTAIN-6 was designed as a cardiovascular safety trial and reported a lower rate of cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke: 6.6% versus 8.9% over 104 weeks.[2] SELECT then asked the harder question in 17,604 people with cardiovascular disease and obesity but no diabetes, and reported a 20% relative reduction in the same composite endpoint over a mean of 39.8 months.[11]

Kidney and heart failure. FLOW, in type 2 diabetes with chronic kidney disease, was stopped early for benefit: major kidney disease events were 24% less frequent, with lower cardiovascular and all-cause mortality.[12] STEP-HFpEF, in obesity-related heart failure with preserved ejection fraction, reported improvements in symptom scores, six-minute walk distance, and C-reactive protein.[9]

Those are large, randomized, placebo-controlled, endpoint-driven trials. On the evidence hierarchy this library uses, almost nothing else in the peptide conversation is in the same category.

Where the evidence is weak

The effect is not durable without the drug. The STEP 1 off-treatment extension followed 327 participants for a year after both the drug and the lifestyle intervention were withdrawn. They regained about two-thirds of the weight they had lost, and the cardiometabolic improvements reverted toward baseline along with it.[6] This is the single most under-discussed finding in the literature, and it reframes the entire question from "how much weight" to "for how long, and then what".

Tolerability drives real discontinuation. Gastrointestinal events are not a footnote: they affected the majority of treated participants in STEP 2 and caused several times more discontinuations than placebo in STEP 1.[4][3] A pharmacovigilance analysis of GLP-1 agonists prescribed for weight loss also reported elevated rates of pancreatitis, bowel obstruction, and gastroparesis. That is a database design that establishes association, not causation, and it is worth reading with that limit in mind.[10]

Body composition is measured, its meaning is not. Lean mass falls along with fat mass, and the reported proportion varies enormously between studies.[14] No trial has been designed with strength or physical function as its primary endpoint, so what this means for a person over five or ten years is genuinely unknown.

Some signals remain unresolved. The rodent thyroid C-cell finding is real, the primate and human data suggest a species difference, and the authors themselves say the long-term consequence of sustained GLP-1 receptor activation in the human thyroid is unknown.[1] The reported association with nonarteritic anterior ischemic optic neuropathy comes from a retrospective cohort at one institution, and the investigators call for further study rather than claiming causation.[15]

Populations are not fully represented. The trials skew toward participants who tolerated escalation and stayed enrolled; long-term data beyond a handful of years, in adolescents, and in people at the margins of the eligibility criteria are thinner than the volume of publication suggests. Pregnancy is the clearest case: pregnant participants were not enrolled in the randomized programme at all, so the entire human record consists of pregnancies that occurred inadvertently during trials plus observational cohorts assembled afterward.[17] Weight loss during pregnancy offers no benefit, restored fertility after weight loss makes unplanned pregnancy more likely, and the labeled direction is to stop well before conception. That combination makes this an absence of evidence with practical consequences, not an academic one.[16]

Legal and regulatory status

Semaglutide is an FDA-approved drug, and its approvals now run well past the weight-management indication that dominates public discussion. Scoped to the populations each one covers, the current US labeling carries:

  • Glycemic control in type 2 diabetes. The original 2017 injectable approval, as an adjunct to diet and exercise in adults. The oral tablet presentations carry the same indication.
  • Cardiovascular event reduction in type 2 diabetes. Reducing the risk of major adverse cardiovascular events in adults who have type 2 diabetes and established cardiovascular disease. This is the SUSTAIN-6 population.[2]
  • Cardiovascular event reduction in obesity or overweight without diabetes. Added in March 2024 on the strength of SELECT, and scoped to adults with established cardiovascular disease and either obesity or overweight. It was the first weight-management drug approved to reduce cardiovascular events.[11]
  • Kidney outcomes in type 2 diabetes with chronic kidney disease. Added in January 2025 on the strength of FLOW, and scoped to reducing the risk of sustained eGFR decline, end-stage kidney disease, and cardiovascular death in adults with both conditions.[12]
  • Chronic weight management. In adults with obesity, or with overweight plus at least one weight-related comorbid condition, and for the injectable in adolescents aged 12 and older with obesity.[3]
  • Noncirrhotic metabolic dysfunction-associated steatohepatitis with moderate to advanced fibrosis. An accelerated approval for the injectable, which by definition means continued approval may depend on a confirmatory trial. This page carries no evidence entry for that indication, because the confirmatory evidence is not what the trials cited here tested.

Two things follow from that list. Each indication belongs to the population its trial enrolled. The cardiovascular indication is not a general cardiovascular-prevention claim, and the kidney indication is not a chronic kidney disease claim outside type 2 diabetes. And the oral and injectable presentations are not interchangeable: they carry overlapping but different indication sets and entirely different dose scales.

The whole list is a categorical difference from the research compounds elsewhere in this library: there is a label, an approved manufacturer, defined indications, a monitored safety programme, and post-marketing surveillance behind it.[13]

It is prescription-only. Legitimate access runs through a licensed prescriber who evaluates whether it is appropriate, selects and escalates the dose, and monitors the response. That is a clinical fact about the drug's status, and this page takes no position on anything outside that channel. Peptide Health Lab does not sell peptides and does not tell anyone where to obtain anything.

Two regulatory details are worth knowing. First, approval is indication-specific: the trials that support weight-management approval enrolled people meeting defined body-mass-index and comorbidity criteria, and use outside those criteria is off-label practice, not approved use. Second, GLP-1 agonists carry a labeled contraindication in people with a personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2, which descends directly from the rodent C-cell work.[1] Athletes in tested sport should check the current year's prohibited list rather than any static page.

Questions to bring to a provider

The evidence here plainly exists. That makes the productive questions ones of fit, duration, and monitoring:

  • What is the specific goal (glycemic control, weight, cardiovascular risk, kidney protection), and which trial population most closely resembles this situation?[11]
  • What is the plan for the long run, given that the STEP 1 extension shows most of the effect reverses within a year of stopping?[6]
  • Is there any personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2?[1]
  • Is there a history of pancreatitis, gallstones, gastroparesis, or significant reflux, and how does that change the calculus?[5]
  • Is pregnancy possible, planned, or current, and is breastfeeding in the picture? If a pregnancy is being planned, how far ahead of conception does the labeled two-month stop need to happen?[16]
  • With existing diabetic retinopathy, what eye monitoring should accompany rapid glycemic improvement?[2]
  • What should happen before any procedure requiring sedation, given the retained gastric content findings?[7]
  • How will protein intake, resistance training, and lean mass be monitored during weight loss?[14]
  • What is the escalation schedule, and what is the plan if gastrointestinal effects become intolerable at a given step?[4]

The strength of the evidence base is exactly why the conversation should be specific. A drug with this many trials also has this many documented caveats, and both halves belong in the same discussion.

Evidence by claim

Grades describe how strong the evidence is; the line under each grade describes what kind of studies it is. How we grade evidence.

Weight reduction in adults with obesity and no diabetes
Human RCT evidence human RCT

STEP 1 enrolled 1,961 adults and randomized them 2:1 to 2.4 mg weekly or placebo for 68 weeks; the semaglutide group lost a mean of 14.9% of body weight versus 2.4% on placebo, and 50.5% of them reached at least 15% loss versus 4.9% on placebo. In oral form, the 50 mg dose-finding arm in OASIS 1 produced a comparable 15.1% mean reduction versus 2.4%, and the 25 mg dose that was subsequently approved produced a 13.6% mean reduction versus 2.2% at week 64 in OASIS 4.

[3] [8] [18]

Weight reduction in adults who also have type 2 diabetes
Human RCT evidence human RCT

Effect sizes are consistently smaller in people with diabetes. STEP 2 reported a mean 9.6% reduction on 2.4 mg weekly versus 3.4% on placebo at 68 weeks. That is clinically meaningful, but well short of the STEP 1 figure that dominates public discussion.

[4]

Cardiovascular event reduction in type 2 diabetes
Human RCT evidence human RCT

SUSTAIN-6 randomized 3,297 patients at high cardiovascular risk and found cardiovascular death, nonfatal myocardial infarction, or nonfatal stroke in 6.6% on semaglutide versus 8.9% on placebo over 104 weeks (hazard ratio 0.74).

[2]

Cardiovascular event reduction in obesity without diabetes
Human RCT evidence human RCT

SELECT enrolled 17,604 patients with pre-existing cardiovascular disease and a body-mass index of 27 or greater but no diabetes. The primary composite endpoint occurred in 6.5% on semaglutide versus 8.0% on placebo over a mean 39.8 months (hazard ratio 0.80). That is the trial that moved the conversation from weight to outcomes.

[11]

Kidney outcomes in type 2 diabetes with chronic kidney disease
Human RCT evidence human RCT

FLOW randomized 3,533 patients and was stopped early at a prespecified interim analysis; major kidney disease events were 24% less frequent on 1.0 mg weekly semaglutide (hazard ratio 0.76), with lower cardiovascular and all-cause mortality as confirmatory secondary outcomes.

[12]

Symptoms and function in obesity-related heart failure with preserved ejection fraction
Human RCT evidence human RCT

STEP-HFpEF randomized 529 patients and reported a 7.8-point greater improvement in the Kansas City Cardiomyopathy Questionnaire clinical summary score and a 20.3 m greater improvement in six-minute walk distance versus placebo at 52 weeks.

[9]

Durability of the effect after treatment stops
Human RCT evidence human RCT

The STEP 1 off-treatment extension followed 327 participants for a year after withdrawal. They regained roughly two-thirds of the weight lost: net loss fell from 17.3% at week 68 to 5.6% at week 120. Most cardiometabolic improvements reverted toward baseline. The investigators read this as evidence that obesity behaves as a chronic condition requiring ongoing treatment.

[6]

Muscle-mass and physical-function consequences of the weight lost
Anecdotal reports only review

Lean-mass changes have been measured in trial substudies but vary widely across studies, and no randomized trial has used strength or physical function as a primary endpoint. What that lean-mass change means for a person's function over years is not established by controlled evidence.

[14]

Risk of nonarteritic anterior ischemic optic neuropathy
Anecdotal reports only human observational

The signal comes from a retrospective matched cohort at a single academic neuro-ophthalmology practice, a design that cannot establish causality and that the authors explicitly flag as hypothesis-generating. No randomized trial has been powered for this outcome.

[15]

Typical protocol range in the research

  • Phase 3 obesity trial without diabetes (STEP 1), 68 weeks of once-weekly subcutaneous injection alongside a lifestyle intervention

    2.4 mg once weekly, reached through a 16-week escalation period [3] [6]

  • Phase 3 obesity trial in adults who also had type 2 diabetes (STEP 2), 68 weeks

    2.4 mg once weekly, compared against placebo and against 1.0 mg once weekly (the dose then approved for diabetes) [4]

  • Cardiovascular outcome trial in type 2 diabetes (SUSTAIN-6), 104 weeks on top of standard care

    0.5 mg or 1.0 mg once weekly [2]

  • Chronic kidney disease trial in type 2 diabetes (FLOW), median follow-up 3.4 years

    1.0 mg once weekly [12]

  • Oral formulation over 68 weeks of daily tablets, in a phase 3 dose-finding arm (OASIS 1) at a strength that was not subsequently approved

    50 mg once daily by mouth, reached by escalation [8]

  • Oral formulation at the strength that was approved for chronic weight management and cardiovascular risk reduction. This is the labeled titration schedule for the tablet presentation, studied in the 71-week OASIS 4 trial with coprimary endpoints at week 64

    25 mg once daily by mouth as the labeled maintenance strength, reached by a labeled schedule that opens at 1.5 mg daily and steps up every 30 days [18]

These are trial schedules and labeled titration schedules: a description of what published protocols and product labeling specify, not a plan for any individual. Every approved presentation starts low and escalates slowly specifically because gastrointestinal tolerability tracks the dose, and the escalation belongs to a prescribing clinician.

Ranges are what published research reports, not a recommendation. PHL does not prescribe, and nothing here is personalized to you.

Side effects & safety signals

  • Gastrointestinal adverse events (nausea, vomiting, diarrhea, constipation)

    The dominant adverse-event category in every trial. In STEP 2, gastrointestinal events were reported in 63.5% of participants on 2.4 mg weekly versus 34.3% on placebo. · Mostly mild to moderate, typically transient, and concentrated during dose escalation. Not trivial, though: in STEP 1, 4.5% of the semaglutide group discontinued treatment because of gastrointestinal events versus 0.8% on placebo. A pharmacovigilance analysis of GLP-1 agonists prescribed for weight loss also reported elevated rates of pancreatitis, bowel obstruction, and gastroparesis relative to a non-GLP-1 comparator.

    [4] [3] [10]

  • Gallbladder and biliary disease

    A meta-analysis of 76 randomized trials and 103,371 patients reported a relative risk of 1.37 for gallbladder or biliary disease across all GLP-1 agonist trials, and 2.29 in trials conducted for weight loss specifically. · Risk was higher at higher doses and with longer treatment. Cholecystitis and cholelithiasis can require surgery, so a history of gallstones or biliary disease is worth raising with a clinician before anything is started.

    [5]

  • Delayed gastric emptying and retained stomach contents before procedures

    In a retrospective single-center review of 404 elective upper endoscopies, increased residual gastric content was found in 24.2% of patients who had received semaglutide within 30 days versus 5.1% of those who had not. · This is an anesthesia and procedural-safety flag rather than a day-to-day side effect: retained stomach contents raise aspiration risk under sedation. Any upcoming surgery, endoscopy, or procedure requiring sedation is a reason to tell both the prescriber and the proceduralist about GLP-1 use well in advance.

    [7]

  • Thyroid C-cell findings in rodents across the GLP-1 class, and the medullary thyroid carcinoma caution (a class finding, not a semaglutide finding)

    The source study is a liraglutide programme, not a semaglutide one. Long-term liraglutide exposure produced C-cell hyperplasia in rats and, to a lesser extent, in mice; 20 months of liraglutide at more than 60 times human exposure levels did not produce C-cell hyperplasia in cynomolgus monkeys. · That work localized the GLP-1 receptor to rodent C-cells and showed GLP-1 receptor agonists stimulate calcitonin release and C-cell hyperplasia, while humans and monkeys showed low thyroid C-cell receptor expression and no calcitonin release in primates. In patients exposed to liraglutide for two years, mean calcitonin stayed at the lower end of the normal range with no difference in the proportion crossing the 20 pg/mL cutoff. The authors nonetheless state plainly that the long-term consequences of sustained GLP-1 receptor activation in the human thyroid remain unknown. This is the class evidence behind semaglutide's labeled contraindication, extrapolated from a different molecule. A personal or family history of medullary thyroid carcinoma or multiple endocrine neoplasia type 2 is a specific reason to raise it with a clinician before considering a GLP-1 agonist at all.

    [1]

  • Pregnancy, planned pregnancy, and breastfeeding

    Not studied. Pregnant participants were not enrolled in the randomized programme; the only human exposure data come from pregnancies that occurred inadvertently during trials, and a review of the regulatory submissions concluded that evidence in women having planned pregnancies is lacking. Large observational cohorts of periconceptional exposure have not consistently shown an increased risk of major congenital malformations, but no prospective human trial exists. · In animal reproduction studies the class produced embryofetal mortality, structural abnormalities, and reduced fetal growth at clinically relevant maternal exposures, and semaglutide's labeling states that it may cause fetal harm, directs discontinuation when a pregnancy is recognized where it is being used for weight reduction or cardiovascular risk reduction, and directs stopping at least two months before a planned pregnancy because of the drug's long half-life. Weight loss itself offers no benefit during pregnancy. Reviewers of the class recommend contraception to prevent unintended pregnancy during treatment, and note that restored fertility after weight loss is exactly why unplanned pregnancies have become more common on these drugs. Pregnancy, intention to conceive, and breastfeeding all belong in the conversation with the prescriber before starting and at every review, not after the fact.

    [16] [17]

  • Diabetic retinopathy complications

    In SUSTAIN-6, retinopathy complications (vitreous hemorrhage, blindness, or conditions requiring intravitreal treatment or photocoagulation) were significantly more frequent with semaglutide (hazard ratio 1.76). · A real signal in a population with long-standing type 2 diabetes and pre-existing retinopathy, generally attributed to the speed of glycemic improvement. Existing eye disease is a reason for an ophthalmology conversation before and during treatment.

    [2]

  • Loss of lean body mass alongside fat mass

    Reported across trials with wide heterogeneity: a review describes lean mass reductions ranging from roughly 15% of total weight lost in some studies to 40–60% in others. · Whether those measured changes translate into loss of strength or physical function has not been tested as a trial endpoint, so the clinical meaning is unresolved. It is a reasonable thing to ask a clinician to monitor rather than assume.

    [14]

  • Reported association with nonarteritic anterior ischemic optic neuropathy

    A retrospective, propensity-matched single-institution cohort reported a higher hazard of NAION among patients prescribed semaglutide (hazard ratio 4.28 in the type 2 diabetes cohort). · The authors are explicit that this is observational and that causality was not established. Sudden painless vision loss is an emergency regardless of cause; the honest framing here is an unresolved signal worth knowing about, not a settled risk.

    [15]

Published lists are never exhaustive, so report anything unexpected to a licensed provider.

Storage, handling & reconstitution

Lyophilized storage
Approved semaglutide is manufactured as a ready-to-use aqueous solution in a prefilled pen, or as an oral tablet. It is not supplied as a freeze-dried powder, so there is no lyophilized form inside the approved supply chain to store. The published trial programme used sponsor-supplied injection pens throughout, and no published study characterizes the stability of powdered material labeled as semaglutide outside that chain.
Reconstituted storage
Pens in the trials were handled as refrigerated pharmaceutical product: kept cold, protected from light, and used within the limited in-use window the product labeling assigns after first use. The specific temperatures and in-use days for any given presentation come from the labeling dispensed with the prescription and from the prescribing clinician. They do not come from this page.
Reconstitution
Not applicable. Approved semaglutide is dispensed as a ready-to-use solution in a prefilled injection pen or as an oral tablet. There is no lyophilized powder and nothing to reconstitute.
Handling notes
Because semaglutide is an approved drug, a real manufacturer stability programme, a real expiry date, and a real labeled in-use period exist for it. That is a meaningful difference from the unapproved compounds elsewhere in this library, and it is worth naming: storage guidance here is a summary of how a labeled product is handled, not an improvised convention.

The how-to guides cover the conventions behind these fields, and what the published stability data does and does not establish: Storage, Reconstitution, Handling.

Goal pages that include Semaglutide

Each one starts from the goal rather than the molecule, and grades what the evidence supports for that goal specifically.

  • Weight Loss

    A research reference for the incretin compounds mapped to weight loss, covering what the registrational trials measured, what happens when treatment stops, what the body-composition data show, and which parts of the picture come from a label rather than from a trial.

Questions for your provider

Bring this page to a licensed provider. A provider can order labs, review your medications and history, and tell you whether anything here is relevant to your situation. This page can't. Peptide Health Lab does not prescribe and does not sell peptides.

Want a structured starting point for that conversation? The Stack Builder turns your goals into a research-cited outline you can review together.

Citations

18 sources · every identifier checked against PubMed

Before you act on any of this

This page is educational only and is not medical advice. It does not diagnose, treat, or prescribe. Review it with a licensed provider before making any health decision. Peptide Health Lab does not sell peptides.

How we grade and verify evidence · Terms of Use · Privacy Policy

Open the Stack Builder