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Side effects

When GLP-1 side effects start, and how long they last

People want a date: when does the nausea start, when does it stop. The honest answer is that side effects follow the dose more closely than the calendar. They tend to arrive in the first weeks, return with each step up, and fade once the dose holds steady — and the labels say exactly that.

By the Cafeity teamUpdated 6 min read

The short answer

GLP-1 side effects usually start in the first days to weeks of treatment and are most common while the dose is being increased. The labels for semaglutide, tirzepatide and orforglipron all describe gastrointestinal reactions as most frequent during dose escalation and decreasing over time.123 They can return briefly after each dose increase. Within a week, some people feel worst a day or two after an injection, when blood levels peak. Side effects that are severe or not easing are a reason to contact your prescriber rather than wait.

Illustration: a stepped line shows a dose rising in stages over 24 weeks; above it, a shaded curve of stomach side effects peaks shortly after each step and shrinks with each later step. Labelled as an illustration of the pattern the labels describe, not a schedule.
An illustration of the pattern the prescribing information describes — side effects cluster after each dose increase and fade as the dose holds. It is not a dosing schedule: the pace of any increase is set by the prescriber.

The pattern the labels describe

Every weight-management GLP-1 is started at a low dose and increased in steps, and the labels are open about why: to reduce gastrointestinal reactions.3 They are just as open about what happens anyway.

What each current US prescribing information says about when gastrointestinal reactions happened in the trials.
MedicineWhat the label says about timing
Semaglutide 2.4 mg injectionGastrointestinal reactions were most frequently reported during dosage escalation.
Tirzepatide injectionThe majority of nausea, vomiting and/or diarrhoea events occurred during dose escalation and decreased over time. Most people who stopped because of side effects did so in the first few months.
Orforglipron tabletNausea, vomiting and diarrhoea were more common during the dosage escalation period and decreased over time.
Liraglutide 3 mg injectionMost gastrointestinal episodes were mild or moderate. Tiredness, weakness, taste changes and dizziness were mainly reported in the first 12 weeks, often alongside gastrointestinal symptoms.

Sources: the prescribing information for each medicine.1234

There is also a physiological reason the early weeks are different. Tirzepatide slows stomach emptying, and its label says the delay is largest after the first dose and diminishes over time.2 The body adapts to part of the effect; the dose increases then push it back up.

The first weeks, roughly

No label gives a day-by-day timetable, and individual experience varies widely. What the trials and the pharmacology do support is a rough shape:

  • The first few days. Some people notice nothing; others feel queasy or full within a day or two of the first dose. Semaglutide reaches its peak level 1 to 3 days after an injection, tirzepatide at a median of about 24 hours, orforglipron 4 to 8 hours after a tablet.123
  • The first month. The medicine is still building up. Semaglutide takes 4 to 5 weeks of weekly doses to reach a steady level; tirzepatide about 4 weeks.52 Appetite changes and gut symptoms often become clearer across this stretch.
  • Each dose increase. Symptoms that had settled often return for a while after a step up. The labels' warnings about dehydration and kidney problems specifically mention the period of starting and increasing the dose.1
  • Once the dose holds. For most people, the gut reactions become less frequent and less intense.23 Some, like constipation, can persist and need managing rather than waiting out.

For the whole first month in more detail — appetite, eating and routines as well as side effects — see your first month on a GLP-1.

Within a week: the dose-day rhythm

On a weekly injection, the level of medicine in the body rises after each dose and drifts down across the week. Semaglutide's half-life of about a week means the peak lands a day or three after the injection and the level at the end of the week is still about half of that peak once treatment has settled.1 Tirzepatide's half-life of about 5 to 6 days gives a slightly larger swing.2

Plenty of people find that swing in their symptoms: queasiest the day after the injection, hungriest the day before the next one. Plenty find no pattern at all. Daily tablets produce a much flatter level, so a dose-day rhythm is less likely. The Cycle View draws this estimated curve from your own dose dates, so your logged symptoms can be read against it.

How long do they last?

The labels do not put a number of weeks on it, and it would be misleading to invent one. What they say is that the most common reactions decrease over time once the dose stops rising.23

Two things are worth separating. Side effects that fade — the first-weeks queasiness, the early tiredness — are the ones the labels describe. Side effects that persist — constipation that never quite resolves, reflux every evening, hair shedding months in — are a different conversation, because they usually respond to changes in eating, fluids or treatment rather than to patience.

And some things should not be waited out at all. The warnings below apply whether it is week one or week forty.

Side effects after stopping

Because semaglutide has a half-life of about a week, it remains in the circulation for about 5 to 7 weeks after the last dose; tirzepatide clears in roughly 4 weeks.12 Its effects on the gut wind down across that time rather than stopping the day the medicine does. For what the trials found about weight and appetite after stopping, see stopping a GLP-1.

When to contact your prescriber

Keeping a record of it

The pattern is personal, so the useful record is personal too. Cafeity places every symptom on the same timeline as your doses and dose changes, so after a few weeks you can see whether your side effects follow the step-ups, the day after the injection, or neither — and bring that to your prescriber.

Cafeity medication-level chart over seven days, labelled "Estimate based on published half-life. Not a measurement", with the last dose, the injection site (stomach, upper left), the next scheduled dose and a side-effect check-in.
The estimated level across the week, with symptoms logged underneath.
Cafeity "Your week, understood" screen: Ora explains that everything is calculated from your own log, offers questions such as "When are my symptoms worst?", and shows the week's protein, energy, water, weight trend, symptom days and a note that protein was 80 g under target.
Ask when your symptoms are worst; the answer comes from your record.

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Common questions

How soon do GLP-1 side effects start?
Often within the first few days of the first dose, though some people notice nothing until a later increase. Peak levels come 1 to 3 days after a semaglutide injection and about a day after tirzepatide.12
Why did my side effects come back?
The most common reason is a dose increase: the labels describe gastrointestinal reactions as most frequent during escalation.1 Illness, a large or fatty meal, alcohol or a change in routine can also bring them back. If they return and do not settle, tell your prescriber.
Is the first week the worst?
For some people. For others the step to a higher dose is harder than the start. The labels describe the escalation period as a whole as the time side effects are most common, rather than any single week.23
Do side effects mean I should stop?
That is a decision for you and your prescriber, not a website. Mild, easing side effects are common and expected; severe or persistent ones, and the warning signs above, need a clinician.

Sources

  1. Semaglutide injection and tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 30 June 2026
  2. Tirzepatide injection for weight management and obstructive sleep apnoea — US prescribing information DailyMed, US National Library of Medicine, version published 2 September 2026
  3. Orforglipron tablets for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 13 August 2026
  4. Liraglutide 3 mg injection for weight management — US prescribing information DailyMed, US National Library of Medicine, version published 15 June 2026
  5. Semaglutide injection for type 2 diabetes — US prescribing information DailyMed, US National Library of Medicine, version published 10 June 2026

Written by the Cafeity team from the sources listed here. Figures from prescribing information are quoted as the label states them; trial results are averages from those trials, not predictions for any one person. This page has not yet been reviewed by a clinician — see the editorial policy for how pages are researched and corrected.