Glucagon: GlucaGen/Baqsimi/Gvoke, emergency blood-sugar rescue hormone

What this is

Glucagon is a 29-amino acid peptide hormone secreted by pancreatic alpha cells. It is the primary counter-regulatory hormone to insulin: when blood glucose falls dangerously low, glucagon signals the liver to release its stored sugar into the bloodstream. Synthetic glucagon has been FDA-approved as an emergency rescue medication since 1960, making it one of the longest-established peptide drugs in clinical use (Isaacs and colleagues 2021). Since 2019, two modernized formulations — Baqsimi intranasal powder (Eli Lilly) and the Gvoke pre-mixed liquid auto-injector and pre-filled syringe (Xeris) — replaced the older lyophilized kit that required powder reconstitution immediately before injection, dramatically improving usability for lay caregivers. Glucagon is also FDA-approved as a diagnostic aid for smooth-muscle relaxation during gastrointestinal imaging procedures. The glucagon receptor is a component target of investigational dual and triple agonist obesity drugs (mazdutide, survodutide, retatrutide), but those are distinct molecules with their own evidence and regulatory tracks.

History

Glucagon was first identified in 1923 by Charles Kimball and John Murlin at the University of Rochester, who noticed a hyperglycemic contaminant in pancreatic extracts being studied for insulin's hypoglycemic effects. They named it "glucagon" for "glucose agonist," and it was characterized as the principal counter-regulatory hormone opposing insulin. The amino acid sequence was determined by Bromer and colleagues in 1957, and crystalline glucagon was isolated and approved by the FDA in 1960 for emergency treatment of severe hypoglycemia (Isaacs and colleagues 2021). For decades the only formulation was a reconstituted lyophilized injection — effective but cumbersome, requiring caregivers to mix powder, draw up solution, and inject within critical minutes. The 2019 approvals of Baqsimi and Gvoke removed the reconstitution step entirely. In parallel, controlled glucagon receptor agonism re-emerged as a therapeutic concept in the 2010s and 2020s through dual GLP-1/glucagon and triple GLP-1/GIP/glucagon agonists, repurposing the hormone's energy-expenditure and hepatic-fat-oxidation effects for chronic obesity treatment (Gasbjerg and colleagues 2026).

What it does

Glucagon is insulin's physiological counterpart. When blood glucose drops, pancreatic alpha cells release glucagon, which tells the liver to break down stored glycogen and release glucose into circulation. This rescue response typically begins within 5–10 minutes of administration, reaching peak glucose elevation at approximately 15–30 minutes (Isaacs and colleagues 2021). Because glucagon's plasma half-life is approximately 8–18 minutes and its glycemic effect resolves within 60–90 minutes, it functions as a bridge — raising blood sugar enough for the patient to recover consciousness and consume oral carbohydrate — rather than a sustained therapy. In adipose tissue, glucagon also promotes lipolysis. The critical dependency: the mechanism requires intact hepatic glycogen stores. In patients with depleted glycogen — from prolonged starvation, severe hepatic disease, chronic alcohol use, or adrenal insufficiency — glucagon cannot mobilize what isn't there, and IV dextrose is the appropriate intervention.

Evidence

• Human: Decades of clinical use as emergency rescue for severe hypoglycemia in insulin-treated diabetic patients, with multiple FDA-approved formulations (Isaacs and colleagues 2021). A systematic review and meta-analysis found glucagon effective for hypoglycemia reversal in insulin-treated patients, with comparable efficacy to IV dextrose and across different formulations (Boido and colleagues 2014). Glucagon is also supported by FDA label evidence for diagnostic smooth-muscle relaxation during GI imaging procedures.
• Animal: Glucagon biology is fundamental to metabolic physiology and is comprehensively characterized in preclinical systems. The proglucagon-derived peptide family — encompassing glucagon, GLP-1, GLP-2, and oxyntomodulin — and their receptors have been extensively studied across species (Gasbjerg and colleagues 2026).
• In vitro: Glucagon receptor (GCGR) signaling has been characterized in hepatocyte and adipose-tissue systems. GCGR is a Class B G-protein-coupled receptor; its activation pathway and cAMP-mediated downstream effects are among the best-characterized hormone signaling cascades in metabolic physiology (Gasbjerg and colleagues 2026).

Myths and misconceptions

• "Glucagon causes weight loss when used regularly." Native single-dose glucagon for hypoglycemia rescue does not produce sustained weight loss — its effect is acute, transient hyperglycemia followed by return to baseline. The weight-loss effects attributed to "glucagon" come from the dual and triple receptor agonist drugs (mazdutide, survodutide, retatrutide), where chronic controlled glucagon receptor agonism combined with GLP-1 agonism is under investigation. Native glucagon as a standalone weight-loss agent has not been clinically validated.
• "Glucagon rescue always works for severe hypoglycemia." Glucagon depends on hepatic glycogen stores to raise blood glucose. In patients with depleted glycogen — from prolonged starvation, severe alcohol use, advanced liver disease, or adrenal insufficiency — glucagon can fail entirely. IV dextrose is the necessary intervention in these scenarios, and emergency services should be summoned without delay.
• "The intranasal Baqsimi formulation is less effective than injection." Nasal mucosal bioavailability is sufficient to produce comparable rescue glucose elevation, and head-to-head usability studies favored the intranasal formulation in lay-caregiver scenarios where the injection kit's reconstitution steps add critical seconds and error potential. Clinical equivalence in real-world emergencies is incompletely characterized, but both routes are considered clinically valid.
• "Glucagon and insulin simply cancel each other out." They have opposing effects on blood glucose but act on different tissues through different receptors with asymmetric time courses. Insulin's effect lasts hours; glucagon's lasts under 90 minutes. Glucagon rescues acute hypoglycemia by mobilizing hepatic glycogen but does not reverse insulin's action — it temporarily elevates blood glucose while insulin continues to act, which is why rebound hypoglycemia within 1–2 hours of rescue is common if oral carbohydrate is not consumed afterward.

Known effects

• Emergency reversal of severe hypoglycemia — FDA-approved (multiple formulations since 1960; modernized 2019 products)
• Diagnostic smooth-muscle relaxation for GI imaging — FDA-approved
• Hepatic glycogenolysis and gluconeogenesis — Mechanistic / preclinical (the core pharmacology underlying rescue use)
• Adipose lipolysis — Mechanistic / preclinical
• Component of dual/triple agonist obesity drug candidates — Phase 3 investigational (survodutide, retatrutide); Phase 3 data ongoing in Western markets; approved separately in China (mazdutide)

Safety signals

Nausea and vomiting are common after glucagon rescue; patients should be positioned on their side after administration. Headache and transient hyperglycemia are commonly reported. Rebound hypoglycemia is a predictable consequence within 1–2 hours of rescue if oral carbohydrate is not consumed, because glucagon does not address the underlying cause of hypoglycemia. Anaphylactic and hypersensitivity reactions have been reported but are rare.

Contraindications from label: Pheochromocytoma (glucagon can stimulate catecholamine release from the tumor, precipitating hypertensive crisis). Insulinoma (glucagon may initially raise blood glucose but can then trigger a paradoxical insulin surge from the tumor, worsening hypoglycemia). Glucagonoma (additional glucagon in a patient already producing pathological excess is contraindicated). Known hypersensitivity to glucagon or formulation excipients. For diagnostic use: conditions where smooth-muscle relaxation is undesirable (severe ileus, mechanical obstruction).

Interaction signals from label: Warfarin — glucagon can potentiate the anticoagulant effect; relevant primarily in repeated diagnostic administration rather than single-dose rescue. Beta-blockers — can blunt the catecholamine response to hypoglycemia and theoretically prolong recovery time after rescue. Indomethacin — can interfere with glucagon's hyperglycemic effect by blocking hepatic glucose output, potentially reducing rescue efficacy.

Regulatory status

• US (FDA): Prescription-only. Multiple approved branded products: GlucaGen (Novo Nordisk, reconstituted injection); Lilly Glucagon Emergency Kit (reconstituted injection); Baqsimi (Eli Lilly, intranasal powder, 2019); Gvoke HypoPen / Gvoke PFS (Xeris, pre-mixed liquid, 2019). Generic injectable glucagon also available. FDA approval for emergency hypoglycemia rescue dates to 1960 (Isaacs and colleagues 2021).
• EU (EMA): Approved. Native glucagon products including GlucaGen are EMA-approved.
• UK (MHRA): Approved.
• Canada (Health Canada): Approved.
• Australia (TGA): Approved.
• WADA: Listed under S2 (peptide hormones, growth factors, related substances and mimetics), prohibited at all times under the WADA code. Therapeutic Use Exemptions are available for insulin-treated diabetic athletes who require glucagon as rescue medication.

The dual and triple receptor agonists incorporating glucagon receptor agonism (mazdutide, survodutide, retatrutide) are separate molecules subject to their own regulatory status and are not covered by this card's regulatory entries.

Mechanism

Glucagon binds to the glucagon receptor (GCGR), a Class B G-protein-coupled receptor expressed on hepatocytes. Receptor activation engages adenylyl cyclase and elevates intracellular cAMP, activating PKA. PKA phosphorylates glycogen phosphorylase (stimulating glycogenolysis) and inhibits glycogen synthase, mobilizing hepatic glycogen into circulating glucose. PKA signaling also activates gluconeogenic enzymes (PEPCK, G6Pase) for de novo glucose production from non-carbohydrate precursors. In adipose tissue, glucagon promotes lipolysis. The proglucagon precursor that encodes glucagon also encodes GLP-1, GLP-2, and oxyntomodulin — peptides with overlapping but distinct receptor profiles and physiological roles (Gasbjerg and colleagues 2026).

The rescue mechanism is critically dependent on intact hepatic glycogen stores. In glycogen-depleted states — prolonged starvation, severe hepatic disease, chronic alcohol use, adrenal insufficiency — the mechanism has no substrate to mobilize and glucagon administration will be ineffective. IV dextrose is the labeled appropriate intervention in those settings.

Open questions

• Real-world equivalence of routes: Whether intranasal Baqsimi and injectable formulations (GlucaGen, Gvoke) are clinically equivalent in real-world emergencies — where caregiver familiarity and ease of administration dominate outcomes — is incompletely characterized.
• Glucagon rescue under GLP-1 receptor agonist therapy: Optimal use of rescue glucagon in patients maintained on GLP-1 receptor agonists, who may have altered counter-regulatory responses, is an emerging area of study.
• Long-term safety of chronic glucagon receptor agonism: Controlled chronic glucagon receptor agonism via dual and triple agonists has different safety considerations from single-dose rescue use; these are being characterized through dedicated Phase 3 programs that are distinct from this card's scope.
• Pediatric mini-dose glucagon: Subcutaneous low-dose glucagon for milder hypoglycemia in young children is used off-label without dedicated approved formulations.
• Population-level rescue impact: Whether routine glucagon prescribing for at-risk patients meaningfully reduces severe hypoglycemia hospitalization rates at the population level is not well quantified.
• Access and uptake: Cost and access barriers remain; many at-risk patients do not carry a current emergency device despite improved formulation usability.

Related peptides

• GLP-1 (glucagon-like peptide-1) — sister proglucagon-derived incretin; acts on GLP-1R to suppress glucagon secretion and stimulate insulin; structural sibling to glucagon from the same precursor gene
• Oxyntomodulin — another proglucagon-derived peptide; a dual GCGR/GLP-1R agonist with glucagon's N-terminal sequence fused to an eight-residue extension
• Retatrutide — investigational triple GLP-1R/GIPR/GCGR agonist incorporating glucagon receptor agonism for chronic obesity; distinct molecule from native glucagon