The Complete Guide to GLP-1 Medications

The short version

GLP-1 is a hormone your own gut already makes. Medications like semaglutide and tirzepatide are engineered copies of it that last about a week instead of a few minutes. That single change — from minutes to a week — is what turns a fleeting after-dinner signal into steady, all-day appetite regulation.

For context, most lifestyle-only programmes produce 3–5% weight loss over the same period, and most of that comes back. These numbers are not a marginal improvement. They are a different category of result — and they are why we built our telehealth programme around them.

What GLP-1 actually is

GLP-1 stands for glucagon-like peptide-1. It is an incretin — a hormone released by cells lining your lower small intestine and colon whenever food arrives. Its job is to coordinate the body's response to a meal, and it does four things at once.

Natural GLP-1 is broken down within about two minutes by an enzyme called DPP-4. That is the design problem the drug companies solved: modify the molecule so the enzyme cannot get a grip on it, and a two-minute hormone becomes a seven-day one. We go deeper on the appetite side of this in Why GLP-1 Medication Quiets the Food Noise.

The two medications that matter

Tirzepatide adds a second hormone receptor, GIP, which appears to improve how the body handles fat and may soften nausea at equivalent effectiveness. It is the more powerful of the two on average — but average is not the same as *better for you*. We lay out the full comparison in Semaglutide vs. Tirzepatide: Which Is Right for You?.

The four brand names in that table cause a great deal of confusion, because they are only two molecules. Ozempic vs. Wegovy: Same Drug, Different Label and Mounjaro vs. Zepbound: Same Drug, Different Label each explain what genuinely differs within a pair — and what does not.

What the research found

These are not new or lightly tested compounds. The GLP-1 class has been in clinical use for diabetes since 2005, and the weight-management trials are large, randomised and published in the *New England Journal of Medicine*. Each one is summarised, with what it measured and how to read it critically, in The GLP-1 Trials, Explained.

• STEP 1 (2021) — 1,961 adults without diabetes on semaglutide 2.4 mg. Mean weight loss 14.9% at 68 weeks, against 2.4% on placebo. Roughly a third of participants lost 20% or more.
• SURMOUNT-1 (2022) — 2,539 adults on tirzepatide. Mean weight loss 20.9% at the 15 mg dose over 72 weeks. About 57% of that group lost at least 20% of their body weight.
• SELECT (2023) — 17,604 adults with existing heart disease and overweight, but *not* diabetes. Semaglutide cut major cardiovascular events — heart attack, stroke, cardiovascular death — by 20%. This was the trial that reframed GLP-1 as more than a weight drug.
• STEP 4 (2021) — participants who stopped semaglutide regained about two-thirds of what they had lost within a year. An important, honest finding, and the reason Maintenance: Keeping the Weight Off is its own conversation.

Who these medications are for

The standard clinical threshold is a BMI of 30 or above, or a BMI of 27 or above alongside a weight-related condition such as high blood pressure, type 2 diabetes, sleep apnoea, high cholesterol or fatty liver disease. A physician makes the call after reviewing your full history — that is the whole point of the consultation.

This list is not a formality and it is not padding. Tell your prescriber everything — the screening only protects you if it has the full picture. Our full medical disclaimer explains what this site can and cannot tell you.

What to expect if you start

1. Weeks 1–4. A deliberately low starting dose. You are not meant to lose much yet — the goal is to let your stomach adapt. Most people notice appetite changes before they notice the scale. See Your First Month on a GLP-1: What to Expect.
2. Weeks 5–12. Dose steps up roughly monthly. This is where consistent weight loss usually begins, typically 1–2 pounds a week. Full schedule in GLP-1 Dosing and Titration, Week by Week.
3. Months 4–9. The steady stretch. Most of the total loss happens here, and habits built now are what hold afterwards — Eating Well on a GLP-1 and Protecting Muscle While You Lose Fat both matter more than people expect.
4. Month 10 onward. Weight settles at a new set point. The conversation shifts from losing to keeping, covered in Maintenance: Keeping the Weight Off.

A month-by-month view of typical results, including the plateaus nobody warns you about, is in The GLP-1 Results Timeline, Month by Month.

Side effects, honestly

Most people get some digestive side effects early on — mild nausea, feeling full quickly, constipation or looser stools. They are usually worst in the first week after a dose increase and fade as your body adapts. Most are manageable with the practical adjustments in Managing GLP-1 Side Effects. Serious complications are rare, and your prescriber screens for them before you start. If what you have read elsewhere is more alarming than this, Ten Myths About GLP-1 Medication checks the common claims against the evidence.

Common questions