What’s a GLP-1? Understanding This Revolutionary Weight Loss and Diabetes Treatment

Last reviewed: June 8, 2026

Last updated: June 8, 2026

Written by: Jay Hastings, CEO of PlexusDx

Jay Hastings is the CEO of PlexusDx, a precision health company focused on genetic testing, blood biomarker insights, and personalized wellness recommendations. He has more than 20 years of experience across healthcare innovation, genomics, laboratory operations, healthcare investing, and strategic finance.

Medically reviewed by: Jayden Lee, PharmD, EMBA

Jayden Lee, PharmD, EMBA, is the PlexusDx Medical Science Liaison with a PharmD and MBA specializing in pharmacogenomics and clinical product development, with a proven ability to bridge the gap between genomic research and practical patient outcomes. Dr. Lee has more than 10 years of professional experience in clinical pharmacy, academia, and research.

A GLP-1 is glucagon-like peptide-1, an incretin hormone your small intestine releases in response to eating. In everyday usage the term has drifted to mean the drug class built to imitate it — GLP-1 receptor agonists — and that slippage causes real confusion, because the hormone and the medications behave very differently in one crucial respect. Native GLP-1 is destroyed within minutes of release. Engineered agonists such as semaglutide have an elimination half-life of approximately one week, as stated in the Ozempic prescribing information. That single difference is what turned a fleeting gut signal into a once-weekly medication.

The Hormone Itself

GLP-1 is secreted by enteroendocrine cells lining the intestine when nutrients arrive. Its best-characterised action is potentiating insulin release from pancreatic beta cells in a glucose-dependent way — the effect scales with how high blood glucose actually is rather than firing indiscriminately. It also suppresses glucagon secretion when glucose is elevated.

That glucose dependence explains a pattern visible across the labels. The Ozempic label frames hypoglycemia risk primarily around concomitant use with insulin or an insulin secretagogue such as a sulfonylurea, and directs that reducing the dose of those agents may be necessary. The incretin pathway does not push glucose downward without regard to where it started.

GLP-1 additionally slows the rate at which the stomach empties and participates in central appetite regulation. Those two effects are why the class ended up mattering for body weight at all, rather than only for glycemia.

Why the Natural Hormone Was Never a Drug

Native GLP-1 is cleaved almost immediately by the enzyme dipeptidyl-peptidase 4. Any therapy built on the unmodified hormone would require continuous infusion, which is not a practical treatment for a chronic condition.

The engineering solution was structural. Semaglutide’s peptide backbone is produced by yeast fermentation, then modified at position 8 to resist DPP-4 degradation and at position 26 with a hydrophilic spacer and a C18 fatty di-acid that binds albumin. Albumin binding is the main protraction mechanism, and it is what stretches minutes into roughly a week.

Absolute bioavailability of semaglutide following subcutaneous administration is 89%. The same molecule taken as a tablet has an absolute bioavailability estimated at approximately 1% to 2%, which is why the oral products use much larger milligram numbers to reach comparable exposure.

What the Approved Medications Treat

The class splits along indications, and the split is worth committing to memory. Ozempic injection covers glycemic control in adults with type 2 diabetes, major adverse cardiovascular event risk reduction in adults with type 2 diabetes and established cardiovascular disease, and renal and cardiovascular death risk reduction in adults with type 2 diabetes and chronic kidney disease.

Wegovy injection covers major adverse cardiovascular event risk reduction in adults with established cardiovascular disease and either obesity or overweight, long-term weight reduction in adults and in pediatric patients aged 12 and older with obesity and in adults with overweight plus at least one weight-related comorbid condition, and noncirrhotic MASH with moderate to advanced fibrosis under accelerated approval.

On the tirzepatide side, Mounjaro is indicated as an adjunct to diet and exercise to improve glycemic control in adults and pediatric patients 10 years and older with type 2 diabetes. Zepbound is indicated for long-term weight reduction and for moderate to severe obstructive sleep apnea in adults with obesity. Same molecule, two labels, two purposes.

Single-Pathway Versus Dual-Pathway Molecules

Semaglutide is a GLP-1 receptor agonist. Tirzepatide is a dual agonist, engaging both the glucose-dependent insulinotropic polypeptide receptor and the GLP-1 receptor. That is a real pharmacological distinction, not a marketing one, and it has been tested head to head.

In SURMOUNT-5, a 72-week open-label phase 3b trial in 751 adults with obesity but without type 2 diabetes, participants received the maximum tolerated dose of tirzepatide or of semaglutide. The least-squares mean percent change in weight at week 72 was −20.2% with tirzepatide and −13.7% with semaglutide. Waist circumference fell −18.4 cm and −13.0 cm respectively.

The most common adverse events in both arms were gastrointestinal, mostly mild to moderate, and occurred primarily during dose escalation. Greater average effect and greater average gastrointestinal burden travel together in this class.

The Safety Architecture Common to the Class

Every semaglutide and tirzepatide label carries a boxed warning about thyroid C-cell tumors observed in rodents, with human relevance undetermined, and contraindicates use in people with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2.

Warnings and precautions run consistently across the labels: acute pancreatitis, acute gallbladder disease, acute kidney injury due to volume depletion, hypersensitivity reactions, severe gastrointestinal adverse reactions, and pulmonary aspiration during general anesthesia or deep sedation in patients undergoing elective procedures. The Ozempic label additionally notes diabetic retinopathy complications reported in a clinical trial.

None of that is a reason to avoid the class. It is the reason the class is prescription-only and the reason the screening conversation with a clinician matters more than any article.

What "Revolutionary" Does and Does Not Mean

The degree of weight reduction achieved in the pivotal obesity trials was without precedent for pharmacotherapy, and the cardiovascular and renal outcome data broadened what the class is for. That is a genuine shift in what medicine can offer.

What has not changed is that obesity and type 2 diabetes remain chronic conditions. The labels position these medications as adjuncts to a reduced-calorie diet and increased physical activity, not as replacements for them, and the withdrawal trials in this field consistently show weight regain after discontinuation. The medication is a tool inside a long-term plan managed with a clinician.

How Your Genetics Relate to GLP-1 Pathways

Not everyone responds to GLP-1 medications the same way. Genetic variants — including GIPR rs1800437, FTO rs9939609, and MC4R rs17782313 — relate to the biological pathways these medications act on. These are pathway-level associations only and do not predict how much weight you will lose or how you will respond to any specific medication. PlexusDx maps 14 pathways, 49 peptides, and 150+ genetic insights so you and your provider can see how your genes relate to these pathways. It does not recommend, prescribe, or determine which medication, dose, or peptide is right for you. The PlexusDx Precision Peptide Genetic Test ($298) gives you and your provider pathway-level genetic context to support a more personalized conversation. Genetics is a guide, not a guarantee.

Access Personalized GLP-1 Care Through PlexusDx

PlexusDx offers seven prescription GLP-1 protocols to all 50 states — no membership, no insurance required, async intake or live consult. The Semaglutide Injection is $189/mo month-to-month, or from $149/mo on the 6-month plan. Medications are dispensed from licensed 503A compounding pharmacies following strict quality and safety standards. Add a Precision Peptide Genetic Test for $298 to personalize your protocol from day one.

Frequently Asked Questions

Is a GLP-1 a hormone or a medication?

Both, depending on usage. GLP-1 is an incretin hormone released by intestinal cells after eating, which potentiates glucose-dependent insulin secretion, suppresses glucagon, slows gastric emptying and participates in appetite regulation. GLP-1 receptor agonists are engineered medications that bind the same receptor but resist rapid enzymatic degradation, giving semaglutide an elimination half-life of approximately one week.

Are all GLP-1 medications the same?

No. They differ by molecule, by route and by approved indication. Semaglutide is a single GLP-1 receptor agonist; tirzepatide is a dual GIP and GLP-1 receptor agonist. Ozempic and Mounjaro carry type 2 diabetes indications, while Wegovy and Zepbound carry weight-management indications. Zepbound is additionally approved for moderate to severe obstructive sleep apnea in adults with obesity.

Which produces more weight loss, semaglutide or tirzepatide?

In SURMOUNT-5, a 72-week open-label trial in 751 adults with obesity and without type 2 diabetes, the least-squares mean percent change in weight at week 72 was minus 20.2% with maximum tolerated tirzepatide and minus 13.7% with maximum tolerated semaglutide. That is an average across a trial population, not a forecast for any one person, and gastrointestinal adverse events were common in both arms.

Why are these medications injected rather than swallowed?

Peptides are poorly absorbed from the gut. Absolute bioavailability of semaglutide is 89% after subcutaneous administration but only approximately 1% to 2% after oral tablet administration, which is why the tablet products use much larger milligram strengths and carry specific administration conditions in their labeling. Oral semaglutide products do exist and are FDA approved; there is no FDA-approved oral tirzepatide.

Do GLP-1 medications work without diet and exercise?

The approved labels position them as adjuncts to a reduced-calorie diet and increased physical activity, and every pivotal weight-management trial delivered both. In the Wegovy program, participants received instruction for an approximately 500 kcal per day deficit and physical activity counselling of at least 150 minutes per week alongside the study drug. The trial results describe that combination, not the drug in isolation.

Medical and Editorial Standards

Medical review process: This article was reviewed for medical accuracy, scientific clarity, evidence alignment, and appropriate discussion of genetics, medications, supplements, biomarkers, and health-related claims.

Sources and evidence: PlexusDx educational content is developed using peer-reviewed research, clinical literature, reputable medical references, and, where applicable, public health or regulatory guidance.

Commercial transparency: PlexusDx offers genetic testing, blood biomarker testing, personalized supplement recommendations, and related precision wellness services. Product mentions are intended to help readers understand available options and should not be interpreted as medical advice.

Important disclaimer: PlexusDx educational content is for informational purposes only and should not be used as a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about medications, supplements, genetic testing, lab testing, or health-related care.