Start low, go slow. Every label starts at a low dose and steps up no faster than every four weeks, and says this is to reduce the risk of stomach and gut side effects.1234
Most side effects come early. In the semaglutide weight trials, gut side effects were mostly mild to moderate, short-lived, and came during or just after the dose steps.5 Tirzepatide's obesity trial reported the same.6
Diabetes medicines change the picture. With insulin or a sulfonylurea, the risk of low blood sugar rises; the labels say the dose of those may need to come down.13
Pregnancy: the semaglutide labels say to stop at least 2 months before a planned pregnancy; the tirzepatide labels say tablets for contraception may work less well after starting and after each step up.1234
On this page
- Before the first dose
- The dose steps, as the labels print them
- Side effects: when they come and when they ease
- Nausea, vomiting and constipation: what the labels say to do
- Low blood sugar and other medicines
- Pregnancy and contraception
- When to call a doctor
- Frequently asked questions
- Related on Grey Peptides
- Sources
Before the first dose
Four GLP-1 injections dominate US prescriptions for weight and diabetes. Wegovy and Ozempic both contain semaglutide, made by Novo Nordisk; Zepbound and Mounjaro both contain tirzepatide, made by Eli Lilly.1234 Wegovy and Zepbound are labelled for weight reduction, among other uses; Ozempic and Mounjaro for type 2 diabetes.1234 The label is what your prescriber and pharmacist work from, and it is what this page quotes.
Three things on the labels are worth knowing before the first injection:
- Who should not take it. Anyone with a personal or family history of medullary thyroid carcinoma, or with MEN 2, should not use these drugs (the boxed warning). Tell your prescriber about either.13
- Training first. The Wegovy and Zepbound labels say patients should be trained on the device they will actually receive, and retrained if it changes.13 A pen and a vial are injected differently; the syringes section covers needles and injecting for anyone who has never done it.
- Never share a pen, even with a new needle: the labels say pen-sharing can pass on blood-borne infections.13
The dose steps, as the labels print them
The tables below are the labels' own steps, printed under the line Manufacturer's recommended dosing (FDA label). Each row is checked against the label's text every time this page is built. Your prescriber may move more slowly than this; the labels allow it.13 The titration planner lays these steps out on a calendar.
Manufacturer's recommended dosing (FDA label): Wegovy injection (semaglutide)
| Step | What the label says | Source |
|---|---|---|
| Weeks 1 to 4 (starting dose) | 0.25 mg once weekly | Wegovy injection prescribing information, section 21 |
| Weeks 5 to 8 | 0.5 mg once weekly | Wegovy injection prescribing information, section 21 |
| Weeks 9 to 12 | 1 mg once weekly | Wegovy injection prescribing information, section 21 |
| Weeks 13 to 16 | 1.7 mg once weekly | Wegovy injection prescribing information, section 21 |
| Week 17 on: maintenance for weight reduction in adults | 1.7 mg or 2.4 mg once weekly (2.4 mg recommended) | Wegovy injection prescribing information, section 21 |
| Optional higher step for adults | up to 7.2 mg once weekly, after at least 4 weeks on 2.4 mg | Wegovy injection prescribing information, section 21 |
| If a step is not tolerated | consider waiting 4 weeks before the next step | Wegovy injection prescribing information, section 21 |
The Wegovy label also has a daily tablet with its own schedule, and rules for switching between tablet and injection; those are in section 2 of the label.1
Manufacturer's recommended dosing (FDA label): Ozempic (semaglutide)
| Step | What the label says | Source |
|---|---|---|
| Weeks 1 to 4 (starting dose) | 0.25 mg once weekly | Ozempic prescribing information, section 22 |
| Week 5 on | 0.5 mg once weekly | Ozempic prescribing information, section 22 |
| If more glucose control is needed, after at least 4 weeks | 1 mg once weekly | Ozempic prescribing information, section 22 |
| If more is still needed, after at least 4 weeks | 2 mg once weekly | Ozempic prescribing information, section 22 |
| Maximum | 2 mg once weekly | Ozempic prescribing information, section 22 |
Manufacturer's recommended dosing (FDA label): Zepbound (tirzepatide)
| Step | What the label says | Source |
|---|---|---|
| Weeks 1 to 4 (starting dose, not a maintenance dose) | 2.5 mg once weekly | Zepbound prescribing information, section 23 |
| Week 5 on | 5 mg once weekly | Zepbound prescribing information, section 23 |
| Each later step | up 2.5 mg, after at least 4 weeks on the current dose | Zepbound prescribing information, section 23 |
| Maintenance for weight reduction | 5 mg, 10 mg or 15 mg once weekly | Zepbound prescribing information, section 23 |
| Maximum | 15 mg once weekly | Zepbound prescribing information, section 23 |
Manufacturer's recommended dosing (FDA label): Mounjaro (tirzepatide)
| Step | What the label says | Source |
|---|---|---|
| Starting dose | 2.5 mg once weekly | Mounjaro prescribing information, section 24 |
| If more glucose control is needed | up 2.5 mg, after at least 4 weeks on the current dose | Mounjaro prescribing information, section 24 |
| Maximum, adults | 15 mg once weekly | Mounjaro prescribing information, section 24 |
Missed doses. The Ozempic label says to take a missed dose within 5 days, and otherwise skip it; the Zepbound and Mounjaro labels allow 4 days (96 hours).234 The Wegovy label says to take it if the next dose is more than 2 days away and skip it if less, and to restart the escalation at a lower dose after two or more missed weeks, again because of gut side effects.1 Ask your prescriber before restarting after a longer gap (our reasoning: the labels tie restarting low to tolerability).
Side effects: when they come and when they ease
The common side effects are in the gut, and they cluster around the start and each step up.
- Weeks 1 to 16 or 20, the escalation. In three pooled semaglutide weight trials, nausea was reported by 43.9% on semaglutide (16.1% on placebo), diarrhoea by 29.7% (15.9%), vomiting by 24.5% (6.3%) and constipation by 24.2% (11.1%). These events were mostly mild to moderate (98.1%), transient, and most frequent during or shortly after dose escalation.5 In SURMOUNT-1, the tirzepatide obesity trial, gut events were the most common side effects, mostly mild to moderate and occurring primarily during escalation.6
- On a steady dose. STEP 4 followed people who had already reached the semaglutide maintenance dose and found it well tolerated.5 Gut side effects did not drive the weight loss: people with and without them lost similar amounts.5
- Who stops. 4.3% of people on semaglutide in STEP 1 to 3 stopped because of gut side effects;5 in SURMOUNT-1, side effects of any kind led 4.3% to 7.1% of the tirzepatide groups to stop, against 2.6% on placebo.6
- Severe gut reactions. In the Wegovy injection weight trials, severe gut reactions were reported by 4.1% against 0.9% on placebo; in the Zepbound weight trials by 1.7% to 3.1%, depending on dose, against 1%.13
- Heart rate. Resting heart rate rose by 1 to 4 beats a minute on average with Wegovy injection. The label asks you to report a racing heartbeat at rest.1
- Gallbladder, later on. Gallstones and gallbladder inflammation were more common on the drugs and are linked to weight loss itself.13 See the long-term risks on the hub.
For scale: in STEP 1, adults without diabetes on semaglutide lost 14.9% of their body weight over 68 weeks, against 2.4% on placebo.7
Nausea, vomiting and constipation: what the labels say to do
The labels' main answer to gut side effects is the dose schedule itself. They start low and step up slowly "to reduce the risk of gastrointestinal adverse reactions", and they give two ways to slow down further: the Wegovy label says to consider waiting four more weeks before a step that is not tolerated, and the Zepbound label says to consider a lower maintenance dose for someone who does not tolerate theirs.13 Neither label is meant to be read as a reason to push through a step that is making you ill (our reasoning).
The labels add one warning that matters for anyone with ongoing nausea, vomiting or diarrhoea: kidney injury, in some cases needing dialysis, has been reported after these drugs, mostly in people who became dehydrated from gut side effects. The labels tell prescribers to watch kidney function in patients who report them, especially while the dose is being started and raised.13 So if you cannot keep fluids down, tell your prescriber that day rather than waiting for the next appointment (our reasoning from that warning).
Constipation was reported by about a quarter of people on semaglutide in the weight trials, against about one in nine on placebo.5 The labels give no constipation-specific instruction beyond the dose schedule;13 ask your prescriber or pharmacist before adding a laxative (our reasoning), since these drugs also change how quickly medicines taken by mouth are absorbed.3 The labels say these drugs are not recommended for people with severe gastroparesis.13
Low blood sugar and other medicines
These drugs lower blood sugar and can cause low blood sugar, and the risk rises with insulin or with medicines that make the pancreas release insulin, such as sulfonylureas.13 The Ozempic and Mounjaro labels say the dose of the sulfonylurea or insulin may need to come down.24 In the Zepbound trial in people with type 2 diabetes, low blood sugar (below 54 mg/dL) was reported by 10.3% of those also taking a sulfonylurea, against 2.1% of those not taking one.3 Low blood sugar has also been reported in adults without diabetes.3 The labels say to learn the signs, and, for people with diabetes, to check blood glucose before starting and during treatment.13
These drugs slow the stomach, which can change how other medicines taken by mouth are absorbed; the Zepbound label singles out drugs with a narrow margin such as warfarin.3 Bring a full list of what you take to the first appointment. The interactions guide goes medicine by medicine.
Pregnancy and contraception
- Planning a pregnancy. Semaglutide stays in the body a long time. The Wegovy and Ozempic labels say to stop at least 2 months before a planned pregnancy.12
- If you become pregnant. The Wegovy and Zepbound labels say weight loss offers no benefit during pregnancy and may harm the fetus, and to stop when a pregnancy is recognised. Human data are too few to judge the risk of birth defects; animal studies raised concerns.13 Both makers run pregnancy registries, listed in the labels.13
- The pill and tirzepatide. Tirzepatide may make contraceptive pills less effective because it slows the stomach, most after the first dose. The Zepbound and Mounjaro labels advise switching to a non-oral method, or adding a barrier method, for 4 weeks after starting and for 4 weeks after each step up.34 Contraception that is not taken by mouth is not affected.3
The birth control guide covers this in more depth.
When to call a doctor
Each of these comes from a warning on the labels. Call your prescriber, or get urgent care, if you have:
- Severe stomach pain that will not go away, with or without vomiting, sometimes spreading to the back: the labels' description of pancreatitis, for which they say to stop the drug.13
- Pain in the upper right belly, fever, yellowing of the skin or eyes, or pale stools: the labels warn of gallstones and gallbladder inflammation and call for gallbladder tests if suspected.13 (The symptom list is our reasoning; the labels name the conditions.)
- Vomiting or diarrhoea that stops you keeping fluids down, or passing much less urine: the labels link kidney injury to dehydration.13
- A lump or swelling in the neck, trouble swallowing, shortness of breath or hoarseness that persists: the symptoms the boxed warning lists.13
- Swelling of the face, lips, tongue or throat, trouble breathing, or a severe rash: the labels warn of serious allergic reactions and say to stop and seek help promptly.13
- Shakiness, sweating, confusion or a fast heartbeat while on insulin or a sulfonylurea: signs of low blood sugar.13
- Changes in vision if you have diabetes and diabetic eye disease: the labels report worsening retinopathy in some trials.13
- A racing heartbeat at rest that does not settle.1
Before any surgery or procedure under sedation, tell the team you take a GLP-1: rare cases of stomach contents being breathed in under anaesthesia have been reported.13 The surgery guide has more.
Frequently asked questions
Why do I have to start on such a low dose?
The labels start low and step up no faster than every four weeks to reduce the risk of nausea, vomiting and other gut side effects. The starting dose of Zepbound is for starting only and is not a maintenance dose.13
How long does the nausea last?
In the semaglutide weight trials, gut side effects were mostly mild to moderate and transient, and came most often during or shortly after the dose steps. Tell your prescriber if it stops you keeping fluids down.15
I missed a dose. What now?
Follow your label. The Ozempic label allows a missed dose within 5 days, the Zepbound and Mounjaro labels within 4 days, and the Wegovy label as long as the next dose is more than 2 days away.1234
Can I take a GLP-1 while trying to get pregnant?
The semaglutide labels say to stop at least 2 months before a planned pregnancy, and the labels say to stop when a pregnancy is recognised.123
Related on Grey Peptides
Sources
Labels are cited by their maker, DailyMed set, version and effective date, read from the label cache; studies by PMID, checked on PubMed. All read November 3, 2026.
- Wegovy injection (semaglutide) US prescribing information (Novo Nordisk; DailyMed set ee06186f, version 19, effective June 18, 2026): sections 2, 5, 7 and 8 and the boxed warning. Read November 3, 2026. Source
- Ozempic (semaglutide) US prescribing information (Novo Nordisk; DailyMed set adec4fd2, version 20, effective June 1, 2026): sections 2, 5 and 8. Read November 3, 2026. Source
- Zepbound (tirzepatide) US prescribing information (Eli Lilly; DailyMed set 487cd7e7, version 40, effective August 28, 2026): sections 2, 5, 7 and 8 and the boxed warning. Read November 3, 2026. Source
- Mounjaro (tirzepatide) US prescribing information (Eli Lilly; DailyMed set d2d7da5d, version 40, effective August 27, 2026): sections 2, 5 and 8. Read November 3, 2026. Source
- Wharton S, Calanna S, Davies M, et al. Gastrointestinal tolerability of once-weekly semaglutide 2.4 mg in adults with overweight or obesity, and the relationship between gastrointestinal adverse events and weight loss. Diabetes Obes Metab. 2022;24(1):94-105. PMID 34514682. Several authors worked for Novo Nordisk. Read November 3, 2026. Source
- Jastreboff AM, Aronne LJ, Ahmad NN, et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387(3):205-216. PMID 35658024. Supported by Eli Lilly. Read November 3, 2026. Source
- Wilding JPH, Batterham RL, Calanna S, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP 1). N Engl J Med. 2021;384(11):989-1002. PMID 33567185. Read November 3, 2026. Source
This section explains GLP-1 medicines in plain words; it is not medical advice, and it does not replace the prescriber or pharmacist who knows your history. Grey Peptides sells nothing, links to no seller and rates none. If you feel unwell after an injection, contact a clinician or Poison Help (1-800-222-1222 in the US); in an emergency call 911.