Recall(New to the series?)
Single GLP-1 agonists hit one receptor: GLP-1R. That drives insulin secretion, glucagon suppression, gastric slowing, and appetite reduction. For a full breakdown of what GLP-1R activation does and how it differs from GIP and glucagon co-agonism, see The Receptor Game.
Single GLP-1 receptor agonists were the proof of concept. Before tirzepatide, before retatrutide, before anyone was seriously discussing triple agonism — these drugs demonstrated that mimicking an endogenous gut hormone could produce clinically meaningful weight loss and glycemic control in millions of patients. Semaglutide in particular moved the needle on what "good" looked like and set the bar that every newer agent is now measured against.
The class is defined by a single target — GLP-1R — with no GIP or glucagon co-agonism. This simplifies the tolerability profile but also caps the efficacy ceiling compared to newer multi-receptor drugs.
Semaglutide — Novo Nordisk
At a glance
| Brand names | Ozempic (T2D), Wegovy (obesity), Rybelsus (T2D oral) |
| Targets | GLP-1R |
| Developer | Novo Nordisk |
| Modality | SC injection weekly / oral tablet daily |
| Approval status | Approved — US, EU, global |
| Key efficacy | 14.9% weight loss at 68 weeks (Wegovy 2.4mg, STEP 1) |
| Indications | Type 2 diabetes, obesity, cardiovascular risk reduction |
How it works
A long-acting GLP-1 analog with a C18 fatty acid chain that binds albumin in the bloodstream, extending half-life to approximately 7 days and enabling once-weekly dosing. Three formulations, same molecule: Ozempic and Wegovy are subcutaneous injections at different dose ceilings (1mg for T2D, 2.4mg for obesity), and Rybelsus is an oral tablet that requires specific fasting conditions to achieve adequate gut absorption.
Trial data
STEP 1 (Wegovy, obesity, non-diabetic): 14.9% mean weight loss at 68 weeks. ~32% of participants lost more than 15% of body weight.
SUSTAIN trials (Ozempic, T2D): ~1.5% HbA1c reduction. Consistently outperformed older agents including exenatide and dulaglutide on both glycemic control and weight.
SELECT trial (cardiovascular outcomes): 20% reduction in MACE in patients with established CVD and obesity but no diabetes — the trial that expanded semaglutide from a metabolic drug into a cardiology drug and significantly elevated its market profile.
Dosing and administration
Wegovy: 0.25mg weekly → 0.5mg → 1mg → 1.7mg → 2.4mg maintenance over 16–20 weeks. Slow titration designed to minimize GI side effects during dose escalation.
Rybelsus: 3mg daily for 30 days → 7mg → 14mg. Must be taken on an empty stomach with a small sip of water, 30 minutes before any food or other medication.
Development status
Fully approved and commercially available globally. Supply shortages have persisted due to manufacturing demand outpacing capacity — a structural constraint Novo Nordisk has been investing heavily to resolve.
Safety profile
Nausea, vomiting, and diarrhea most common — highest during dose escalation, typically self-resolving within 4–8 weeks. Black box warning for thyroid C-cell tumors based on rodent data (clinical significance in humans unclear). Rare pancreatitis. Worsening of diabetic retinopathy observed in some T2D patients with rapid glycemic improvement.
Liraglutide — Novo Nordisk
At a glance
| Brand names | Victoza (T2D), Saxenda (obesity) |
| Targets | GLP-1R |
| Developer | Novo Nordisk |
| Modality | SC injection, once-daily |
| Approval status | Approved — US (Victoza 2010, Saxenda 2014) |
| Key efficacy | ~8% weight loss at 56 weeks (Saxenda 3mg, SCALE trial) |
| Indications | Type 2 diabetes, obesity, cardiovascular risk reduction |
How it works
A GLP-1 analog with a C16 fatty acid chain extending half-life to ~13 hours — long enough for once-daily dosing but not weekly. The predecessor to semaglutide, using the same albumin-binding approach with a shorter fatty acid chain and lower systemic exposure. This difference in exposure is the primary reason its efficacy ceiling is lower than semaglutide's.
Trial data
SCALE Obesity (Saxenda 3mg): ~8% mean weight loss at 56 weeks. ~63% of participants lost at least 5% of body weight.
LEADER trial (Victoza, cardiovascular outcomes): ~13% reduction in MACE in T2D patients with high CV risk — the first GLP-1 drug to demonstrate cardiovascular benefit, setting the precedent that semaglutide later built on.
Dosing and administration
0.6mg/day for one week, increasing in 0.6mg weekly steps to 3mg/day maintenance over 5 weeks. Daily injection is the primary practical disadvantage vs semaglutide — adherence over months of treatment is meaningfully lower than once-weekly alternatives.
Development status
Approved and commercially available. Increasingly displaced by semaglutide on formularies where access allows, but remains widely prescribed where cost or supply is a barrier. Pediatric obesity approval (Saxenda) in patients 12 and older.
Safety profile
GI profile similar to semaglutide. Same thyroid C-cell black box warning. Daily injection increases injection site burden vs weekly alternatives.
Exenatide — AstraZeneca
At a glance
| Brand names | Byetta (twice-daily), Bydureon BCise (weekly ER) |
| Targets | GLP-1R |
| Developer | AstraZeneca (acquired from Amylin Pharmaceuticals) |
| Modality | SC injection, twice-daily (Byetta) or weekly (Bydureon) |
| Approval status | Approved — US (Byetta 2005, Bydureon 2012) |
| Key efficacy | ~2–3kg weight loss; HbA1c -0.8–1.5% |
| Indications | Type 2 diabetes only |
How it works
Derived from exendin-4, a peptide found in Gila monster saliva that naturally resists DPP-4 degradation — not a human GLP-1 analog but a structurally distinct peptide that binds and activates the same receptor. The first approved GLP-1RA, it proved the class worked. Not approved for obesity, reflecting its modest weight loss effect relative to what came later.
Trial data
DURATION trials (T2D): HbA1c reduction of 0.8–1.5%. Weight loss of approximately 2–3kg — comparable to older diabetes drugs, well below what semaglutide achieves.
EXSCEL trial (cardiovascular outcomes): Non-inferior to placebo on MACE — did not demonstrate the positive cardiovascular signal seen with newer GLP-1 agents.
Dosing and administration
Byetta: 5mcg twice daily for 4 weeks → 10mcg twice daily. Must be taken within 60 minutes before morning and evening meals. Twice-daily dosing is the primary adherence barrier.
Bydureon BCise: 2mg once weekly via single-dose autoinjector. Extended-release microspheres provide steady drug levels — eliminates the twice-daily burden of Byetta but causes injection site nodules in some patients.
Development status
Approved and commercially available. Declining use as semaglutide and tirzepatide have captured the market. Remains in use in cost-sensitive settings and where newer agent access is limited.
Safety profile
GI side effects most pronounced with Byetta due to twice-daily peak drug concentration. Bydureon causes palpable injection site nodules from the microsphere formulation in a subset of patients. Same thyroid black box warning as class. Immunogenicity (antibody formation against the non-human peptide) occurs in some patients, rarely clinically significant.
Dulaglutide — Eli Lilly
At a glance
| Brand names | Trulicity |
| Targets | GLP-1R |
| Developer | Eli Lilly |
| Modality | SC injection, once-weekly |
| Approval status | Approved — US 2014 |
| Key efficacy | ~3kg weight loss; HbA1c -1.1–1.4% (AWARD trials) |
| Indications | Type 2 diabetes, cardiovascular risk reduction |
How it works
A GLP-1 analog fused to an Fc antibody fragment — the Fc domain extends half-life to approximately 5 days, enabling once-weekly dosing. Structurally distinct from semaglutide's albumin-binding approach but achieving a similar pharmacokinetic goal. The Fc fusion also reduces immunogenicity compared to exendin-4-based drugs.
Trial data
AWARD trials (T2D): HbA1c reduction of 1.1–1.4%. Weight loss of approximately 3kg — comparable to exenatide, below semaglutide.
REWIND trial (cardiovascular outcomes): 12% reduction in MACE in T2D patients with or at risk for cardiovascular disease — notably including patients without established CVD, broadening the cardiovascular benefit claim beyond what competitors had shown.
Dosing and administration
0.75mg or 1.5mg weekly via single-dose pen with a hidden needle — one of the easier injection devices in the class, reducing injection anxiety for patients new to self-injection. No dose titration required for the 0.75mg starting dose.
Development status
Approved and commercially available. Increasingly displaced by tirzepatide (also Eli Lilly) given that Lilly's own dual agonist substantially outperforms it on both weight loss and glycemic control. Still widely used in T2D management where tirzepatide cost or access is a barrier.
Safety profile
GI profile generally milder than twice-daily exenatide and broadly comparable to semaglutide, with lower discontinuation rates in some head-to-head trials. Same class warnings. No novel safety signals in post-marketing surveillance.
Ecluglutide — Sciwind Biosciences
At a glance
| Brand names | Not yet globally branded |
| Targets | GLP-1R (cAMP-biased agonist) |
| Developer | Sciwind Biosciences / Pfizer (global partnership) |
| Modality | SC injection, once-weekly |
| Approval status | Approved — China 2025. Not yet approved US/EU |
| Key efficacy | ~15.4% weight loss (Phase 3, China) |
| Indications | Obesity |
How it works
The first cAMP-biased GLP-1R agonist — a mechanistically distinct approach within the single-agonist class. Standard GLP-1R agonists activate multiple downstream pathways simultaneously: cAMP (which drives insulin secretion and satiety) and β-arrestin (which mediates receptor internalization and contributes to some GI effects). Biased agonism means selectively activating the cAMP pathway while minimizing β-arrestin recruitment — in theory delivering comparable efficacy with a cleaner GI tolerability profile.
Trial data
Phase 3 data from China: ~15.4% mean weight loss — competitive with Wegovy's 14.9% in STEP 1. Tolerability data suggested lower treatment discontinuation rates due to GI adverse events vs unbiased comparators, consistent with the biased agonism hypothesis. Global Phase 3 trials pending through Pfizer partnership.
Dosing and administration
Once-weekly subcutaneous injection. Specific titration schedule and dose ceiling not yet public for the global development program.
Development status
| Milestone | Status |
|---|---|
| China approval | 2025 |
| Pfizer global partnership | Active |
| US/EU Phase 3 | Pending initiation |
| FDA filing | Timeline not yet public |
Safety profile
Phase 3 data from China shows GI side effect profile consistent with GLP-1 class, potentially lower discontinuation rates. Full global safety database pending Phase 3.
What defines this family
Single GLP-1 agonists share a tolerability signature — nausea and vomiting during dose escalation, typically resolving within 4–8 weeks — that is a direct consequence of GLP-1R's role in slowing gastric motility. The efficacy ceiling, roughly 15% weight loss at the highest approved semaglutide dose, is the defining constraint. Getting meaningfully past that number requires additional receptor targets — which is what the dual and triple agonist families are built to provide.
Ecluglutide's biased agonism is the most mechanistically novel development within this class — same receptor, potentially better tolerability by selectively engaging only the pathways responsible for efficacy.
Summary(Family summary)
Semaglutide is the current standard at ~15% weight loss with proven cardiovascular benefit. Liraglutide and dulaglutide are mature, widely available alternatives with their own cardiovascular outcome data. Exenatide is historically significant but largely superseded. Ecluglutide's cAMP-biased mechanism is the most interesting within-class development — same receptor, potentially cleaner tolerability. Every drug in the next three posts exists because the single-receptor ceiling is real.