Semaglutide — Complete Research Guide (2026)

Last updated 2026-06-25

What is Semaglutide?

Semaglutide is a GLP-1 (glucagon-like peptide-1) receptor agonist. Unlike most peptides in this encyclopedia, it is an extensively trialed, regulator-approved medicine, marketed as Ozempic and Rybelsus (type 2 diabetes) and Wegovy (chronic weight management).

Its molecular formula is C187H291N45O59 and it is acylated to bind albumin, which extends its plasma half-life to roughly 7 days and supports once-weekly subcutaneous dosing (or once-daily oral dosing as Rybelsus).

Because semaglutide is FDA-approved, the evidence base is unusually strong: multiple large phase-3 randomized controlled trials underpin every major claim below.

How does Semaglutide work?

Semaglutide mimics the incretin hormone GLP-1, enhancing glucose-dependent insulin secretion, suppressing glucagon, slowing gastric emptying and acting on central appetite pathways to reduce energy intake.

These combined effects lower blood glucose and reduce body weight. [INFOGRAPHIC: GLP-1 receptor signalling and appetite pathway]

What does the research say about Semaglutide?

• In the STEP 1 phase-3 RCT (n=1,961), once-weekly semaglutide 2.4 mg produced a mean body-weight reduction of 14.9% versus 2.4% with placebo at 68 weeks. ^[1]
• In the STEP 4 randomized-withdrawal trial, continuing semaglutide maintained and extended weight loss, whereas switching to placebo led to weight regain. ^[2]
• In the SELECT trial (n=17,604) of adults with cardiovascular disease and overweight/obesity without diabetes, semaglutide produced sustained mean weight loss of 10.2% versus 1.5% for placebo at 208 weeks. ^[4]

[UNIQUE ANALYSIS] Across STEP 1, 4, 5 and SELECT, semaglutide demonstrates a property rare among the compounds catalogued here: durable, placebo-controlled efficacy at multi-year follow-up in tens of thousands of participants. The contrast with research-only peptides on this site is instructive — it shows what a complete regulatory evidence package looks like.

Clinical research & studies

The references below are the primary sources cited throughout this guide. Each links directly to PubMed or the regulator. Where evidence is preclinical (animal or in-vitro), that is stated rather than implied.

• [1] Once-weekly semaglutide in adults with overweight or obesity (STEP 1) — Wilding JPH et al., N Engl J Med 2021. (phase-3 RCT, n=1,961)
• [2] Effect of continued weekly subcutaneous semaglutide vs placebo on weight-loss maintenance (STEP 4) — Rubino D et al., JAMA 2021. (phase-3 randomized-withdrawal RCT)
• [3] Two-year effects of semaglutide in adults with overweight or obesity (STEP 5) — Garvey WT et al., Nat Med 2022. (phase-3 RCT, n=304)
• [4] Long-term weight-loss effects of semaglutide in obesity without diabetes (SELECT) — Ryan DH et al., Nat Med 2024. (pre-specified analysis of RCT, n=17,604)
• [5] Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2) — Frías JP et al., N Engl J Med 2021. (phase-3 open-label RCT, n=1,879)

Dosing context

Approved products use a gradual dose-escalation schedule to mitigate gastrointestinal effects, reported here only as published research context.

This is not medical advice or a usage recommendation. Semaglutide is a prescription medicine and should only be used under the supervision of a licensed prescriber.

Side effects & safety profile

The most common adverse effects across the trial program are gastrointestinal — nausea, diarrhoea, vomiting and constipation — typically dose-related and most pronounced during dose escalation.

Approved labels carry warnings, including a boxed warning regarding thyroid C-cell tumors observed in rodents; prescribing is contraindicated in personal/family history of medullary thyroid carcinoma or MEN 2.

These safety data apply to the approved, pharmaceutical-grade products under medical supervision. Material sold as "research" semaglutide is not quality-assured and is outside this evidence base.

Stacking & combinations

Semaglutide is most directly compared with the dual GIP/GLP-1 agonist tirzepatide; the SURPASS-2 head-to-head trial is the key reference. Combining incretin agents outside a trial is not supported by evidence.

Finding Semaglutide vendors

User reviews

Frequently asked questions

References

1. [1] Once-weekly semaglutide in adults with overweight or obesity (STEP 1) — Wilding JPH et al., N Engl J Med 2021. PMID: 33567185. View sourceStudy: phase-3 RCT, n=1,961Mean weight reduction 14.9% vs 2.4% placebo at 68 weeks.
2. [2] Effect of continued weekly subcutaneous semaglutide vs placebo on weight-loss maintenance (STEP 4) — Rubino D et al., JAMA 2021. PMID: 33755728. View sourceStudy: phase-3 randomized-withdrawal RCTContinued treatment maintained weight loss; placebo switch led to regain.
3. [3] Two-year effects of semaglutide in adults with overweight or obesity (STEP 5) — Garvey WT et al., Nat Med 2022. PMID: 36216945. View sourceStudy: phase-3 RCT, n=304Mean weight change −15.2% vs −2.6% placebo at week 104.
4. [4] Long-term weight-loss effects of semaglutide in obesity without diabetes (SELECT) — Ryan DH et al., Nat Med 2024. PMID: 38740993. View sourceStudy: pre-specified analysis of RCT, n=17,604Sustained mean weight loss 10.2% vs 1.5% placebo at 208 weeks.
5. [5] Tirzepatide versus semaglutide once weekly in patients with type 2 diabetes (SURPASS-2) — Frías JP et al., N Engl J Med 2021. PMID: 34170647. View sourceStudy: phase-3 open-label RCT, n=1,879Semaglutide 1 mg achieved meaningful HbA1c and weight reduction as the active comparator.

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