Patient guide · Reviewed October 2026

GLP-1 medicines, explained.

Wegovy, Zepbound and the new Wegovy pill, in plain language. How they work, who they're for, how dosing goes, what side effects feel like, how to protect your muscle, and what the research says happens if you stop.

13 short chaptersAbout 20 minutesBuilt on FDA labels and published trials

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PJYour guide
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01What GLP-1 is

A hormone your gut already makes.

When you eat, cells in your intestine release a hormone called GLP-1 (glucagon-like peptide-1). It tells your brain you're getting full, helps your pancreas release insulin when blood sugar rises, and slows how fast your stomach empties.

Your own GLP-1 only lasts about two minutes before an enzyme breaks it down.11 The medicines are built to resist that enzyme, so one dose keeps working for days. That's why most of them are taken once a week.

How long one dose lasts1 day after
Your own GLP-1
Tirzepatide
Semaglutide

How much of one dose is left, using each one's half-life: about 2 minutes, about 5 days and about 1 week.3,4,11 This is simplified. With a dose every week, levels build up and stay fairly steady.

Three common myths

Tap a card to flip it.

PJ

PJThink of it as turning up a signal your body already sends, and making it last all week instead of two minutes.

Native GLP-1(7–36) amide is cleared by DPP-4 with a half-life of roughly 2 minutes. Semaglutide (acylated, albumin-binding) has an elimination half-life of about 1 week; tirzepatide (GIP/GLP-1 receptor agonist, C20 fatty diacid) about 5 days. Both reach steady state after about 4–5 weeks of once-weekly dosing.3,4,11

02How it works

One signal, five places it shows up.

GLP-1 receptors are spread through the body, so the medicine does more than one thing. Tap a glowing point on the body, or pick one below.

Gigi

GigiBecause your stomach empties slower, smaller meals and stopping when you first feel full make a big difference to how you feel.

03Who it's for

Is it made for me?

For weight management in adults, the FDA approved Wegovy and Zepbound for people with a BMI of 30 or more, or a BMI of 27 or more with at least one weight-related condition.3,4 Try it with your own numbers. Nothing you type leaves this page.

BMI check

Weight-related conditions (tick any you've been told you have):

–
BMI

Enter your weight and height.

BMI is a rough screening number. It doesn't measure muscle or where fat sits, and a prescriber looks at your whole health picture.14 Some people are also prescribed these medicines for other approved uses, such as type 2 diabetes, heart risk or sleep apnea.

Who should not take them

  • You or a family member has had medullary thyroid cancer (MTC), or you have MEN 2. Both medicines carry a boxed warning about thyroid C-cell tumours seen in rodents.3,4
  • You've had a serious allergic reaction to the medicine or its ingredients.
  • You're pregnant, trying to become pregnant or breastfeeding. Talk to your prescriber first; they're not used in pregnancy.

Tell your prescriber if you have

  • Had pancreatitis, gallbladder problems or kidney problems
  • Diabetic eye disease (retinopathy), or take insulin or a sulfonylurea, which raise the risk of low blood sugar
  • Depression or thoughts of self-harm, now or before
  • A surgery or procedure coming up (these medicines slow the stomach, which matters for anaesthesia)
  • Use birth control pills. Zepbound can make them less effective after you start and after each dose increase4
Labelled indications (adults, chronic weight management, adjunct to reduced-calorie diet and increased activity): initial BMI ≥30 kg/m², or ≥27 kg/m² with ≥1 weight-related comorbidity (e.g. hypertension, T2D, dyslipidaemia, OSA, CVD). Wegovy also carries indications for MACE risk reduction in adults with established CVD and either obesity or overweight, and for MASH with moderate-to-advanced fibrosis; Zepbound for moderate-to-severe OSA in adults with obesity. Wegovy is also approved for paediatric patients ≥12 y (BMI ≥95th percentile). Check current labels before prescribing.3,4

04The medicines

Three options, two molecules.

You'll hear a lot of brand names. Underneath, the weight-loss versions come down to two active ingredients: semaglutide and tirzepatide.

How
Pen, under the skin
How often
Once a week
Usual target dose
2.4 mg (or 1.7 mg)
Average result*
−14.9% at 68 weeks

Acts on the GLP-1 receptor. Also approved to lower the risk of heart attack and stroke in people with heart disease and excess weight. The same ingredient, at lower doses, is sold as Ozempic for type 2 diabetes.

*Average change in body weight in the main trials, with diet and activity advice. Placebo groups lost 2.4% to 3.1%. Individual results vary widely. See chapter 09.1,2,9

What about compounded versions?

Compounded semaglutide and tirzepatide are mixed by pharmacies and are not FDA-approved. The FDA hasn't reviewed them for safety, quality or how well they work, and it has received reports of dosing errors.12 If you're using one, tell your prescriber exactly what it is and how it's measured.

PJ

PJNo version is "the best" for everyone. Cost, coverage, needles vs. pills, other health conditions and side effects all count. That's a conversation for you and your prescriber.

05Dosing

Start low, step up slowly.

Everyone starts on a small dose that goes up every four weeks or so. The first doses are there to let your stomach get used to the medicine, not to cause much weight loss yet. Drag the slider to see where you'd be.3,4

Week 1

The labels describe the usual schedule. Your prescriber may stay at a step longer, go back a step if side effects are rough, or keep you at a lower dose that's working.

Missed a dose?

Missed-dose helper

For the Wegovy pill, follow the leaflet that comes with it. If you've missed more than two weeks of an injection, call your prescriber before your next dose; they may restart you at a lower step.

06The weekly shot

Smaller, quicker than you'd think.

The pens use a very thin needle and go just under the skin, not into muscle. Most people say the worry beforehand is worse than the shot. Pick the same day each week, any time of day, with or without food.3,4

Where it can goTap an area

Stomach, at least 2 inches (5 cm) from the belly button. Front of the thighs. Back of the upper arms, often easier with someone's help.

Use a different spot each week, even if it's the same area. Avoid skin that's tender, bruised, scarred or hard.

How a shot goes

  1. Check the pen: right medicine, right dose, not expired, and the liquid is clear and colourless.
  2. Wash your hands. Pick a spot and wipe it with an alcohol swab if you like; let it dry.
  3. Follow your pen's Instructions for Use. Each pen works a little differently, so the leaflet's pictures are worth a look the first time.
  4. Press the pen flat against the skin and hold it there until it tells you it's finished, usually up to about 10 seconds.
  5. Throw the used pen in a sharps container, or a sturdy plastic bottle if you don't have one.
Gigi

GigiKeep pens in the fridge and never freeze them. Each pen's leaflet says how long it can stay at room temperature if you're travelling.

07Side effects

The bumps, and how to smooth them.

Stomach side effects are the most common. They show up most when you start and after each dose increase, and for many people they ease as the body adjusts.3,4 Pick a symptom to see how often it happened in the trials, and what helps.

How common?

Other common ones: tummy pain, bloating, burping, heartburn, tiredness, headache and dizziness. In the main Wegovy trial, 6.8% of people stopped because of side effects.3

Call your prescriber or get care right away for

  • Severe stomach pain that won't go away, with or without vomiting. It can spread to your back. This can be pancreatitis.
  • Pain in the upper right belly, fever, yellow skin or eyes, or clay-coloured stools: possible gallbladder problems.
  • Can't keep fluids down, or you're peeing much less. Dehydration can strain the kidneys.
  • Swelling of the face, lips, tongue or throat, trouble breathing or a severe rash. Call 911.
  • A lump or swelling in the neck, trouble swallowing, or a hoarse voice that lasts.
  • Shakiness, sweating, confusion or a fast heartbeat if you also take insulin or a sulfonylurea: possible low blood sugar.
  • Changes in vision if you have diabetes, or new or worse low mood or thoughts of self-harm. If you're in crisis, call or text 988.

08Protect your muscle

Lose the fat. Keep the strength.

When you lose weight any way, some of it is fat-free (lean) mass, not just fat. In a body-scan sub-study of the main Wegovy trial, about 39% of the weight lost was lean mass.1 Lean mass isn't all muscle (it includes water and organs), but it's a good reason to protect muscle on purpose. Two things help most: enough protein and strength training.

~39%
lean mass
~61%
fat mass
Share of total weight lost in the STEP 1 body-composition sub-study (DEXA scans).
Your protein range
–grams a day

A common target during weight loss is 1.2 to 1.6 g of protein per kg of body weight a day, spread over meals, about 25–30 g each.10

With a lot of weight to lose, many dietitians base this on a goal or "adjusted" weight, which gives a lower number. If you have kidney disease, ask before raising protein.

Build a day

Tap foods to add them (tap again to add another). Values are approximate.15

Protein0 g
Fiber0 g of 25 g

Strength training

US guidelines suggest muscle-strengthening activity on 2 or more days a week, working all the major muscle groups, plus 150 to 300 minutes of moderate activity like brisk walking.13 Bands, body weight and machines all count. Start where you are.

Gigi

GigiWhen you're full fast, eat the protein first. And bring fiber up slowly with plenty of water, or constipation gets worse before it gets better.

09What to expect

Real results, real ranges.

These are the average changes in body weight in the big trials. Everyone also got advice on diet and activity, including the placebo groups.

Zepbound 15 mg−20.9%
Zepbound 10 mg−19.5%
Zepbound 5 mg−15.0%
Wegovy 2.4 mg−14.9%
Wegovy pill 25 mg−13.6%
Placebo−2 to 3%

SURMOUNT-1 (72 weeks), STEP 1 (68 weeks) and OASIS 4 (64 weeks). These were separate trials with different people, so they aren't a head-to-head comparison.1,2,9

What would an average look like for me?

Enter a weight to see the trial averages in pounds or kilograms.

Averages hide a wide spread. In STEP 1, most people lost at least 5% of their weight, about a third lost 20% or more, and some lost very little.1 Weight usually falls fastest in the first months, then levels off after about a year.

More than a number on the scale

  • Heart: in SELECT, semaglutide 2.4 mg lowered heart attacks, strokes and heart deaths by 20% in 17,604 people with heart disease and excess weight (6.5% vs 8.0% over about 3 years).5
  • Sleep apnea: Zepbound is FDA-approved to treat moderate-to-severe obstructive sleep apnea in adults with obesity.4
  • Blood sugar, blood pressure and cholesterol markers often improve with weight loss.1,2
STEP 1: n=1,961, BMI ≥30 or ≥27 + comorbidity, no diabetes; −14.9% vs −2.4% at week 68 (treatment-policy estimand); ≥5% loss 86.4% vs 31.5%, ≥20% loss 32.0% vs 1.7%. SURMOUNT-1: n=2,539; −15.0/−19.5/−20.9% vs −3.1% at week 72. OASIS 4 (oral semaglutide 25 mg): −13.6% vs −2.4% at week 64. SELECT: n=17,604, established CVD, BMI ≥27, no diabetes; MACE HR 0.80 (95% CI 0.72–0.90), mean follow-up 39.8 months.1,2,5,9

10If you stop

It works while you take it.

Obesity is a long-term condition, and these medicines treat it the way blood-pressure pills treat high blood pressure. Two trials tested what happens when people stop.

SURMOUNT-4 (tirzepatide)

This doesn't mean you can never change course. People stop for cost, side effects, pregnancy plans and many other reasons. It means stopping is worth planning with your prescriber, including what you'll keep doing for protein, activity and follow-up.

PJ

PJThe habits you build now, like protein at every meal and lifting a couple of times a week, are the ones that travel with you whatever you decide later.

11Your appointment

Walk in ready.

Tick the questions you want to ask, then print them or copy them into your notes.

Bring a record, not a guess

Prescribers decide on dose changes from how you're actually doing. A simple daily log of your dose, side effects, protein, water and weight makes that conversation faster and more useful. GLTrax does this from a 60-second check-in and turns it into a report you can share at your visit.

Try GLTrax free

12Quick check

Six questions. No pressure.

See what stuck. Each answer explains itself.

13Sources

Where this comes from.

Every number on this page comes from an FDA label or a published trial. Last reviewed October 2026. Labels change, so check the current one for your medicine.

  1. Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med 2021;384:989–1002. NEJM · PMC
  2. Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med 2022;387:205–216. NEJM
  3. Wegovy (semaglutide) Prescribing Information. Novo Nordisk; FDA. FDA label (PDF)
  4. Zepbound (tirzepatide) Prescribing Information. Eli Lilly and Company. Label (PDF)
  5. Lincoff AM, et al. Semaglutide and cardiovascular outcomes in obesity without diabetes (SELECT). N Engl J Med 2023;389:2221–2232. ACC summary
  6. Wilding JPH, et al. Weight regain and cardiometabolic effects after withdrawal of semaglutide: the STEP 1 trial extension. Diabetes Obes Metab 2022;24:1553–1564. PMC
  7. Aronne LJ, et al. Continued treatment with tirzepatide for maintenance of weight reduction in adults with obesity (SURMOUNT-4). JAMA 2024;331:38–48. JAMA
  8. Wegovy and Zepbound labels, sections 2 (dosage and administration), 5 (warnings) and 6 (adverse reactions), for the dosing, missed-dose and side-effect figures. See 3 and 4.
  9. OASIS 4 trial of oral semaglutide 25 mg, as reported at the FDA approval of the Wegovy pill. Healio
  10. Mozaffarian D, et al. Nutritional priorities to support GLP-1 therapy for obesity: a joint advisory. Am J Clin Nutr 2025. PubMed
  11. Review of GLP-1 receptor agonist pharmacology, including native GLP-1 and DPP-4. PMC
  12. US Food and Drug Administration. FDA's concerns with unapproved GLP-1 drugs used for weight loss. FDA
  13. US Department of Health and Human Services. Physical Activity Guidelines for Americans, 2nd edition. health.gov
  14. Centers for Disease Control and Prevention. Adult BMI categories. CDC
  15. US Department of Agriculture. FoodData Central (approximate values for common portions). USDA
This guide is for general education. It isn't medical advice and doesn't replace your prescriber, pharmacist or the leaflet that comes with your medicine. Never start, stop or change a medicine or dose without talking to your prescriber. Wegovy is a trademark of Novo Nordisk; Zepbound, Mounjaro and Ozempic are trademarks of their owners. GLTrax isn't affiliated with either company.
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