GLP-1 tool guide
GLP-1 side effects day by day: is what I'm feeling normal?
Written by Ankita Verma · Reviewed by Dr Himani Nayyar, BHMS · Updated
For people already prescribed GLP-1 medication. Weight Easy does not prescribe, sell or arrange medication; your prescriber is responsible for treatment decisions.
In brief
Nausea, vomiting, diarrhoea, reflux and sulphur burps are most common 1 to 3 days after a GLP-1 injection and in the first 1 to 2 weeks after a dose increase. Constipation tends to build later in the week. Most stomach side effects ease over time, but severe stomach pain, signs of dehydration or yellow skin need a doctor straight away.
Open the free GLP-1 Side Effects Day by Day →Why side effects follow your injection day
GLP-1 medicines slow how fast your stomach empties. That effect is strongest when the drug level peaks, in the first 1 to 3 days after each weekly shot. Nausea, reflux and burps cluster there, while constipation often appears later as slower digestion and lower food intake add up.
Side effects are also strongest in the first weeks on a new dose. That is why GLP-1s start at a low dose and step up slowly, usually every 4 weeks for weekly injections (Saxenda steps up weekly, and the tablets every 30 days).
Your first week on a GLP-1, day by day
A typical first week on a starting dose looks like this:
- Day 1: mild nausea or tiredness can start within hours.
- Days 2 and 3: nausea and fullness peak; some people get reflux, burps or loose stools.
- Days 4 and 5: stomach settles for most people; constipation may begin.
- Days 6 and 7: fewest stomach symptoms, but appetite starts to return.
How to make side effects easier
Most side effects respond to the same basics: smaller and plainer meals, eating slowly, stopping at the first sign of fullness, steady water through the day, enough protein and fibre, and daily movement. If a dose increase is hard, talk to your prescriber; staying on a dose longer is sometimes an option.
Frequently asked questions
FAQ
How long does nausea last on Mounjaro?
For most people nausea is strongest 1 to 3 days after the injection and fades over the first few weeks on each dose. Tell your prescriber if it stops you eating or drinking.
Why do GLP-1s cause sulphur burps?
Food sits in the stomach longer, so sulphur-containing foods such as eggs, cabbage and onions break down and release gas. Smaller meals, and cutting back on those foods on days 1 to 3 if burps bother you, usually help.
Is constipation on Ozempic normal?
Yes, it is one of the common side effects and often builds later in the week. More water, gradual fibre and daily walking help. See a doctor urgently if you have severe pain or swelling in your belly, cannot pass stool or wind, or keep vomiting.
Do side effects come back with each dose increase?
Often, yes. Stomach side effects often return for a week or two after each step up, then usually settle again.
When should I stop my GLP-1 and call a doctor?
Get help straight away for severe stomach pain that won't go away, pain spreading to your back, yellow skin or eyes, signs of dehydration, or signs of an allergic reaction.
Sources and limits
- Ozempic, Wegovy, Mounjaro and Zepbound prescribing information: adverse reactions and warnings sections.
- Timing guidance reflects common patient experience and label information; individual experience varies.
This guide is educational, not a diagnosis, prescription or dose-change instruction. Always follow your medication leaflet and clinician.