Glossary entry
GLP-1 (glucagon-like peptide-1)
Definition
A naturally-occurring gut hormone that slows gastric emptying, reduces appetite, and improves insulin response. GLP-1 receptor agonist medications mimic this hormone.
See also
Related terms
GIP (glucose-dependent insulinotropic polypeptide)
A gut hormone that stimulates insulin release after meals. Tirzepatide is a dual GIP/GLP-1 receptor agonist; semaglutide acts only on GLP-1 receptors.
A1C (HbA1c)
A blood test that measures average blood glucose over the past 2-3 months. A1C ≥6.5% indicates diabetes. GLP-1 medications typically lower A1C by 1-2 percentage points.
BMI (Body Mass Index)
A screening calculation of body weight relative to height (kg/m²). FDA-approved weight-management GLP-1s require BMI ≥30, or ≥27 with a weight-related comorbidity.
Bioavailability
The proportion of a drug that reaches systemic circulation in active form. Injectable GLP-1s (Wegovy, Mounjaro) have higher bioavailability than oral semaglutide (Rybelsus).
Compounded medication
A medication custom-prepared by a licensed compounding pharmacy, often using the same active ingredient as a brand-name drug. The FDA allowed compounded semaglutide during the 2022-2025 shortage; access has tightened since.
Comorbidity
A second medical condition occurring with the primary one. Hypertension, type 2 diabetes, dyslipidemia, and obstructive sleep apnea are common weight-related comorbidities that lower the BMI threshold for GLP-1 eligibility to 27.