The GLP-1 is glucagon-like peptide-1, which the body uses to regulate appetite and caloric intake, and GLP-1 medications are drugs that act on its receptor. It is a hormone made in the intestine and released after a meal. Semaglutide and tirzepatide are the two GLP-1 medications that BrightSide providers prescribe.
What is GLP-1 in the body?
GLP-1 is a hormone, a peptide of 30 amino acids made by endocrine cells in the lining of the intestine. It is released in response to a meal. A review in Physiological Reviews describes its main actions as stimulating insulin secretion and inhibiting glucagon secretion. The review also reports that GLP-1 inhibits gastrointestinal motility and appears to be a physiological regulator of appetite and food intake. The body inactivates natural GLP-1 very quickly, through an enzyme called dipeptidyl peptidase 4. Semaglutide is built to last longer. The Wegovy label describes it as a GLP-1 analogue with 94 percent sequence homology to human GLP-1, modified to resist that enzyme and to bind to albumin in the blood. It is a GLP-1 receptor agonist, which means it binds to and activates the receptor that natural GLP-1 targets.
How does GLP-1 apply to compounded treatment?
GLP-1 medications reach patients in two ways, as FDA-approved drugs and as compounded drugs. Wegovy, a semaglutide medicine, and Zepbound, a tirzepatide injection, are FDA approved. Compounded semaglutide and compounded tirzepatide are made by a state-licensed pharmacy for one patient on a prescription, and they are not FDA approved. FDA says this means the agency does not review compounded drugs for safety, effectiveness or quality before they are marketed. It also says a compounded drug might be appropriate if a patient's medical need cannot be met by an FDA-approved drug, or the FDA-approved drug is not commercially available. Both kinds are on our shelf. Zepbound is the FDA-approved option, and compounded semaglutide and compounded tirzepatide are the compounded options. A provider reviews your health history and decides whether to prescribe, and which one.
What should a patient check?
Check who prescribes the medication, which pharmacy fills it and whether it is FDA approved. FDA recommends getting a prescription from a doctor and filling it at a state-licensed pharmacy. Its red flags for telehealth include a company that requires no screening and prescription by a licensed doctor, a company with no licensed doctor available to answer questions after the medication arrives, and a company that claims a compounded drug matches an FDA-approved drug. FDA also recommends not using an injectable GLP-1 drug that arrives warm or with insufficient refrigeration. Ask any company which pharmacy fills the prescription, then look up that pharmacy's license with its state. Our pharmacy network page covers how we choose pharmacies, and our pricing page lists every plan. For Washington and Oregon, our Washington page names Nordic Pharmacy in Poulsbo, Washington.
| Semaglutide | Tirzepatide | |
|---|---|---|
| Acts on | The GLP-1 receptor | The GIP receptor and the GLP-1 receptor |
| An FDA-approved brand | Wegovy, marketed by Novo Nordisk | Zepbound, from Eli Lilly |
| Forms on the label | Once-weekly injection and once-daily tablet | Once-weekly injection |
| Compounded version | Not FDA approved | Not FDA approved |
Common questions
Is GLP-1 a hormone or a medication?
Both uses are common. GLP-1 itself is a hormone the intestine releases after a meal. The medications are GLP-1 receptor agonists, drugs that bind to and activate the receptor the hormone targets. When people say they are on a GLP-1, they mean one of those medications, such as semaglutide or tirzepatide.
Is tirzepatide a GLP-1?
Tirzepatide acts on two receptors, GIP and GLP-1, and the Zepbound label calls it a GIP receptor and GLP-1 receptor agonist. FDA's consumer information groups semaglutide and tirzepatide together as GLP-1 drugs, and this glossary does too. Semaglutide acts on the GLP-1 receptor alone.
Related terms
- Semaglutide: a GLP-1 receptor agonist medication.
- Tirzepatide: a medication that acts on the GIP and GLP-1 receptors.
- Wegovy: an FDA-approved semaglutide brand.
- Zepbound: an FDA-approved tirzepatide brand.
Sources
- Holst JJ. The physiology of glucagon-like peptide 1. Physiological Reviews, 2007: https://pubmed.ncbi.nlm.nih.gov/17928588/ (DOI https://doi.org/10.1152/physrev.00034.2006)
- Wegovy (semaglutide) prescribing information, Novo Nordisk, revised 6/2026, on DailyMed: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=ee06186f-2aa3-4990-a760-757579d8f77b
- Zepbound (tirzepatide) prescribing information, Eli Lilly, revised 8/2026, on DailyMed: https://dailymed.nlm.nih.gov/dailymed/drugInfo.cfm?setid=487cd7e7-434c-4925-99fa-aa80b1cc776b
- FDA, FDA's concerns with unapproved GLP-1 drugs used for weight loss, content current as of October 1, 2026: https://www.fda.gov/drugs/drug-alerts-and-statements/fdas-concerns-unapproved-glp-1-drugs-used-weight-loss
Compounded medications are not FDA approved. They are prescribed by a licensed clinician and filled by a licensed 503A pharmacy.
