The Complete Glossary of Weight Loss Medication Terms Every Patient Should Know

A hormone produced in the gut after eating that signals fullness to the brain, slows stomach emptying, and stimulates insulin release. GLP-1 receptor agonist medications (semaglutide, tirzepatide) mimic this hormone at much higher levels than the body produces naturally.

A second gut hormone that enhances insulin secretion and has complementary effects on appetite and fat metabolism. Tirzepatide (Zepbound/Mounjaro) targets both GLP-1 and GIP receptors, which may explain its superior weight loss compared to GLP-1-only drugs.

A medication that activates GLP-1 receptors in the brain and gut. Includes semaglutide (Wegovy, Ozempic, Rybelsus), liraglutide (Saxenda), and the investigational orforglipron. These drugs don't replace your natural GLP-1 — they amplify the signal.

A drug that activates two hormone receptors simultaneously. Tirzepatide is a GLP-1/GIP dual agonist. CagriSema combines GLP-1 with an amylin analog. Dual agonists generally produce greater weight loss than single-target drugs.

A drug targeting three hormone receptors — GLP-1, GIP, and glucagon. Retatrutide (in Phase 3 trials) is the leading example, producing up to 28.7% body weight loss by adding glucagon's metabolic rate-boosting effects to the dual-agonist approach.

Most GLP-1 drugs (semaglutide, tirzepatide) are peptides — modified versions of natural hormones. Orforglipron is a small molecule — a chemically distinct compound that activates the same receptor. Small molecules are generally cheaper to manufacture and easier to formulate as pills.

The active ingredient in Wegovy (weight loss), Ozempic (diabetes), and Rybelsus (oral diabetes). Available as weekly injection and daily pill. Produces approximately 15–17% body weight loss.

The active ingredient in Zepbound (weight loss) and Mounjaro (diabetes). A GLP-1/GIP dual agonist. Produces approximately 20–22.5% body weight loss — the highest of any currently approved medication.

A stimulant appetite suppressant and the most-prescribed weight loss drug in America (~740,000 monthly prescriptions). FDA-approved for 12 weeks of use. Produces 5–7% weight loss. Available as generic for $10–50/month.

An oral combination drug targeting the brain's reward and appetite pathways. Particularly effective for emotional and reward-driven eating patterns. Produces 5–6% weight loss.

An oral combination of phentermine and topiramate. Produces 7–10% weight loss. Generic available since May 2025 at $50–100/month. Absolutely contraindicated in pregnancy due to topiramate's teratogenicity.

Eli Lilly's investigational oral GLP-1. Can be taken at any time of day without food restrictions — a key advantage over the Wegovy pill. FDA approval expected mid-2026. Phase 3 showed 7.5–11.2% weight loss.

The gradual increase of medication dose over time. All GLP-1 medications start at a low dose and increase every 4 weeks to minimize side effects (especially nausea). Titration schedules vary by medication — semaglutide titrates over ~16 weeks from 0.25 mg to 2.4 mg.

The target dose at which the medication produces its full therapeutic effect. For Wegovy, this is 2.4 mg/week. For Zepbound, it's 10 or 15 mg/week. Most patients reach maintenance dose after 3–5 months of titration.

A patient who doesn't achieve meaningful weight loss (typically defined as less than 5% body weight) after 12 weeks on the maintenance dose. This affects 10–17% of patients on semaglutide. Non-response may indicate a different obesity phenotype that responds better to another medication class.

A patient who loses significantly more than the average on medication — typically 20% or more on semaglutide. This occurs in 32–39.6% of patients. Super-response may be linked to specific obesity phenotypes (hunger-driven obesity) and genetic factors.

The body's reduction in metabolic rate beyond what's expected from weight loss alone. After significant weight loss, the body burns fewer calories than a person of the same weight who was never heavier. This can persist for years (as seen in the "Biggest Loser" study).

The hypothesis that the brain defends a particular body weight range through metabolic, hormonal, and behavioral adjustments. When weight drops below this range, hunger increases and metabolism slows. GLP-1 medications may work partly by lowering this defended set point.

A condition where the brain stops responding to leptin (the fullness hormone) despite high levels in the blood. Similar to insulin resistance in diabetes. Contributes to persistent hunger and difficulty maintaining weight loss.

The "hunger hormone." Produced mainly by the stomach, it signals the brain to eat. Ghrelin levels rise after weight loss and remain elevated for months or years — a major driver of weight regain.

Loss of muscle mass and function. A concern during rapid weight loss, especially for patients over 60. Studies show 15–60% of weight lost on GLP-1 medications may be lean mass, making resistance training essential during treatment.

Weight in kilograms divided by height in meters squared. BMI ≥25 = overweight, ≥30 = obese. Standard eligibility metric for weight loss medication, but widely criticized for ignoring muscle mass, fat distribution, and ethnic variation.

A newer metric incorporating waist circumference and height to better estimate visceral (abdominal) fat. BRI above 6.9 is associated with significantly elevated mortality risk. Gaining traction as a BMI supplement or replacement.

A composite endpoint in clinical trials including cardiovascular death, non-fatal heart attack, and non-fatal stroke. The SELECT trial showed Wegovy reduces MACE by 20% — a landmark finding that expanded semaglutide's approved uses.

Hemoglobin A1c — a blood test measuring average blood sugar over 2–3 months. Normal is below 5.7%, prediabetes is 5.7–6.4%, and diabetes is 6.5%+. GLP-1 medications lower HbA1c significantly, which is why they were originally developed for diabetes.

A requirement from your insurance company that your doctor must get approval before they'll cover a medication. Almost universal for GLP-1 weight loss drugs. Typically requires documentation of BMI, comorbidities, and failed prior weight loss attempts. Initial denial rates of 30–40% are common; appeals often succeed.

An insurance requirement to try cheaper medications before they'll approve a more expensive one. For example, your plan may require you to try phentermine or Contrave before they'll cover Wegovy or Zepbound. Duration requirements vary by plan.

The list of medications your insurance plan covers. Weight loss drugs are often in higher tiers (meaning higher copays) or excluded entirely. Formularies change annually — a drug not covered this year might be covered next year.

The CMS (Centers for Medicare & Medicaid Services) program expanding Medicare GLP-1 coverage. The GLP-1 Bridge launches July 2026 ($50/month copay). Full Part D coverage under the BALANCE Model begins January 2027.

The federal government's self-pay portal connecting patients to manufacturer discount programs for weight loss medications. Doesn't sell drugs directly — it links to NovoCare, LillyDirect, and other manufacturer programs. Average GLP-1 cost through the portal: $250–350/month injectable, $149 oral.

A pharmacy that creates customized medications by combining, mixing, or altering ingredients. During the semaglutide shortage (2022–2025), compounding pharmacies produced semaglutide at $99–299/month. The FDA is now restricting this practice since the shortage has resolved.

A state-licensed pharmacy that compounds medications for individual patients based on specific prescriptions. Since April 2025, 503A pharmacies cannot compound semaglutide copies unless there's a documented patient-specific need that FDA-approved drugs can't meet.

A larger-scale compounding operation registered with the FDA that can distribute compounded drugs without patient-specific prescriptions. Enforcement discretion for semaglutide ended May 2025. Most mass-market compounded GLP-1 products came from 503B facilities.

The chemical compound in a drug that produces its therapeutic effect. Semaglutide is the API in Wegovy, Ozempic, and Rybelsus. The FDA has raised concerns about compounders using non-approved salt forms of semaglutide (like semaglutide sodium) rather than the approved base form.

Novo Nordisk's Phase 3 clinical trial program for semaglutide in obesity. STEP 1 showed 14.9% weight loss. STEP 5 showed 15.2% sustained at 2 years. STEP 1 extension data showed two-thirds of weight regained at 1 year after stopping.

Eli Lilly's Phase 3 program for tirzepatide in obesity. SURMOUNT-1 showed up to 22.5% weight loss. SURMOUNT-5 was the head-to-head vs. semaglutide: tirzepatide won at 20.2% vs. 13.7%. SURMOUNT-4 showed 50%+ weight rebound after stopping.

Eli Lilly's Phase 3 program for retatrutide (triple agonist). TRIUMPH-4 showed 28.7% weight loss at 68 weeks. Seven additional readouts expected in 2026. If successful, retatrutide could be submitted for FDA approval in late 2026 or 2027.

A method of analyzing clinical trial results that includes all participants who were randomized, regardless of whether they completed the study. ITT numbers are lower than per-protocol numbers because they include dropouts. ITT is considered the more conservative and realistic analysis.

Analysis of trial results that includes only participants who completed the treatment as designed. These numbers are higher than ITT because they exclude people who dropped out or stopped taking the medication. Both numbers are legitimate — ITT reflects real-world adherence; per-protocol reflects the drug's potential in compliant patients.

Novo Nordisk's landmark cardiovascular outcomes trial for semaglutide. Showed a 20% reduction in MACE (major adverse cardiovascular events) — making Wegovy the only weight loss medication with proven heart protection. Led to expanded FDA labeling.