GLP-1 Side Effects and How a GLP-1 Tracker Helps You Control Them
The most common GLP-1 side effects are nausea, diarrhea, vomiting and constipation, and for most people they're temporary: strongest in the first weeks and after each dose increase, then easing as the body adjusts. In weight-loss trials, 25–29% of people on tirzepatide (Zepbound, Mounjaro) and 44% on semaglutide 2.4 mg (Wegovy, Ozempic) had nausea, and more than 9 in 10 stayed on treatment (Zepbound prescribing information; Wegovy prescribing information). Side effects are a normal part of getting used to a GLP-1 medication, and they're far easier to handle once you can see your own pattern. The Glapp GLP-1 app lets you log every side effect next to your doses on any GLP-1 medication.
Key numbers
| Number | What it means |
|---|---|
| Up to 44% | of people had nausea in weight-loss trials of GLP-1 medications, the most common side effect |
| 69,022 | users currently tracking GLP-1 side effects in Glapp |
| 93–95% | stayed on treatment in those trials despite side effects |
GLP-1 side effects compared: tirzepatide vs semaglutide
The two GLP-1 molecules approved for weight loss are tirzepatide (sold as Zepbound and Mounjaro) and semaglutide (sold as Wegovy and Ozempic). Here's how often each side effect was reported in the trials behind their prescribing information, at the highest weight-loss dose, with placebo in brackets:
| Side effect | Tirzepatide 15 mg | Semaglutide 2.4 mg |
|---|---|---|
| Nausea | 28% (8%) | 44% (16%) |
| Diarrhea | 23% (8%) | 30% (16%) |
| Vomiting | 13% (2%) | 24% (6%) |
| Constipation | 11% (5%) | 24% (11%) |
| Abdominal pain | 10% (5%) | 20% (10%) |
| Indigestion (dyspepsia) | 10% (4%) | 9% (3%) |
| Fatigue | 7% (3%) | 11% (5%) |
| Dizziness | 4% (2%) | 8% (4%) |
| Bloating | 4% (2%) | 7% (5%) |
| Burping | 5% (1%) | 7% (<1%) |
| Gas | 4% (2%) | 6% (4%) |
| Acid reflux (GERD) | 5% (2%) | 5% (3%) |
| Hair loss | 5% (1%) | 3% (1%) |
| Stopped because of side effects | 6.7% (3.4%) | 6.8% (3.2%) |
Sources: Zepbound prescribing information, Table 1; Wegovy prescribing information, Table 3.
These come from separate trials with different people, so compare the pattern rather than the exact numbers. Two differences stand out: headache was on semaglutide's list (14% vs 10% on placebo) but not tirzepatide's, and injection site reactions were on tirzepatide's (6–8% vs 2%) but not semaglutide's. In both, most stomach side effects happened while the dose was being increased.
Why do GLP-1 medications cause side effects?
GLP-1 medications are GLP-1 receptor agonists: they mimic GLP-1, a gut hormone (an incretin) that signals fullness to the brain and slows how quickly the stomach empties (gastric emptying). Tirzepatide also acts on a second incretin, GIP. Those actions are what cut appetite and food noise, and they explain most side effects:
- Slower gastric emptying brings fullness, nausea, burping, heartburn and constipation.
- A gut that's adjusting brings diarrhea, bloating and gas, mostly in the first weeks of each dose.
- Eating far less means fewer calories, less fluid and often less protein, which can lead to tiredness, headaches, dizziness and, a few months in, temporary hair shedding (telogen effluvium).
- Dose escalation restarts the adjustment, which is why every GLP-1 starts low and goes up slowly, and why side effects often return for a week or two after each step.
How strongly you feel them depends on your dose, how fast it goes up, how much your eating changes and how well you keep up with fluids, which is why two people on the same medication can have very different experiences.
How long do GLP-1 side effects last?
For most people, GLP-1 side effects last a few weeks after starting and after each dose increase, then fade. They follow your medication level: strongest in the days after each shot, calmer as the week goes on, and steadier once you've been on the same dose long enough to reach a steady level.
| Tirzepatide (Zepbound, Mounjaro) | Semaglutide (Wegovy, Ozempic) | |
|---|---|---|
| Peak level after a shot | 8–72 hours (median 24 hours) | 1–3 days |
| Half-life | About 5 days | About 1 week |
| Steady level at the same dose | About 4 weeks | About 4–5 weeks |
| Time to leave the body after a last dose | About 1 month | About 5 weeks |
| Dose steps | 2.5 mg every 4+ weeks, up to 15 mg | Every 4 weeks; Wegovy reaches 2.4 mg at week 17 |
Sources: Zepbound prescribing information; Wegovy prescribing information.
The exception is hair shedding, which starts two to four months in and takes six to twelve months to grow back fully.
Track your GLP-1 side effects with a GLP-1 tracking app and stay in control: your 30-day plan
Whichever GLP-1 you take, side effects follow a rhythm: your shot, your dose step, your week. A dose tracker like Glapp makes that rhythm visible: log how you feel each day next to your doses, and you're in control. You'll know which day after your shot each side effect peaks, which step brought it on and whether it's easing, and you'll walk into your next appointment with facts instead of guesses.
Why Glapp? It's a top-rated GLP-1 app used by 100,000+ people, rated 4.8/5 on Trustpilot and the App Store, and 4.6/5 on Google Play. Glapp grew out of Reddit GLP-1 support groups and is built by people who take GLP-1 medications themselves, so it works the way you take your medication: Zepbound, Mounjaro, Wegovy or Ozempic pens, or tirzepatide and semaglutide from a vial, with a built-in dosage calculator that turns your vial's concentration into exact units. You get daily side-effect check-ins, an estimated medication level, custom titration curves and a doctor's report you can share. It's grounded in published clinical trial data and peer-reviewed research, core tracking is free, and it syncs across iPhone, Android and web. Here's how to use it over your first 30 days.
Glapp does not provide medical advice or treat side effects. It shows your daily check-ins against your estimated medication levels so you have structured data to share with your prescriber.
Day 1: Start tracking your side effects
Use Glapp's daily check-in to record any side effect you notice, from nausea to tiredness, and rate how severe it feels. Log your dose and injection time too, so everything that follows is based on what you actually took.
Daily entries help you see whether each side effect is getting better, getting worse or staying the same. You'll have a clear record of how you felt, without having to remember every day.
Day 3: Compare symptoms with your estimated medication level
Glapp estimates your medication level throughout the day using your dose and injection time. Tirzepatide typically peaks 8–72 hours after an injection, semaglutide 1–3 days after.
Seeing your symptoms alongside this estimate helps you spot when each side effect appears within your shot cycle. As you log more days, you can look for a repeating pattern and know when to pay closer attention.
The medication level is an estimate, not a blood test, and a matching pattern does not prove what caused your symptoms.
Day 7: See how your side effects change over time
Open the side-effects chart in the Progress tab and choose the period you want to review. Your daily ratings appear on a timeline, making it easier to see whether a difficult day was an isolated episode or part of a longer trend.
Day 14: Look for patterns in your weekly report
Glapp's weekly progress report brings your logged data together, with dedicated sections showing your side effects and how they change.
Do side effects return on the same day after your shot? Did they start after a dose step? Do they coincide with changes in hunger or food noise? Reviewing two weeks of entries can help you spot patterns that are easy to miss day by day, and give you specific questions to discuss with your doctor.
Day 30: Bring a clear record to your doctor
After a month, review the bigger picture: are your side effects becoming less frequent, staying the same or getting worse? GLP-1 medications reach a steady repeating level after about four to five weeks at the same dose.
Create a doctor's report in Glapp and choose the information to include. Your doctor can review your symptom history alongside your doses and progress, giving you a more focused conversation about your treatment and your next dose step.
Start tracking your GLP-1 side effects in Glapp
Frequently asked questions
What are the most common side effects of GLP-1 medications?
Nausea, diarrhea, vomiting and constipation, followed by abdominal pain, indigestion and fatigue. In weight-loss trials, nausea affected 25–29% of people on tirzepatide and 44% on semaglutide 2.4 mg.
How long do GLP-1 side effects last?
Usually a few weeks per dose. They're strongest in the first one to two weeks after starting and after each increase, peak in the days after each shot, and settle once you've been on the same dose for about a month. Hair shedding is the exception: it starts later and takes months to grow back.
Which GLP-1 has the fewest side effects?
There's no single answer. In separate trials, stomach side effects were reported less often with tirzepatide than with semaglutide 2.4 mg, but the trials enrolled different people, and both had similar rates of people stopping because of side effects (about 7%). The GLP-1 with the fewest side effects for you is the one you tolerate best, and your own log is the clearest way to tell.
Do GLP-1 side effects go away?
Yes, for most people. Most stomach side effects happen while the dose is going up and ease over time, and 93–95% of people in the weight-loss trials stayed on treatment.
Are side effects the same on compounded GLP-1s?
The molecule is the same, so the same side effects are expected. The difference is dosing: tirzepatide or semaglutide from a vial is measured in units, and a mix-up between units and mg can mean a bigger dose and stronger side effects.
When should I call my doctor about GLP-1 side effects?
Call promptly if you can't keep fluids down, have severe or lasting stomach pain, pain in your upper right abdomen, yellowing skin or eyes, a racing heart at rest, or a lump in your neck. Swelling of your face or throat or trouble breathing needs emergency care.
How do I track GLP-1 side effects?
Log them in Glapp's daily check-in and rate each one low, medium or high, next to your dose. Glapp shows each rating against your estimated medication level, and your weekly reports show which day after the shot each side effect peaks.
About the data
Ratings are self-reported and medication levels are estimated from dose and timing, not measured. Trial figures come from the prescribing information of FDA-approved tirzepatide and semaglutide for weight loss. This page is for information only and is not medical advice; talk to your prescriber about any side effect.
About the author
We're GLP-1 patients and health tech professionals, building Glapp in collaboration with doctors. About us
Sources
- Eli Lilly. Zepbound (tirzepatide) prescribing information: Table 1, warnings and precautions, pharmacokinetics.
- Novo Nordisk. Wegovy (semaglutide) injection prescribing information: Table 3, warnings and precautions, pharmacokinetics.
- Jastreboff AM, et al. Tirzepatide once weekly for the treatment of obesity (SURMOUNT-1). N Engl J Med. 2022;387:205–16. Trial summary.
- Wilding JPH, et al. Once-weekly semaglutide in adults with overweight or obesity (STEP 1). N Engl J Med. 2021;384:989–1002.
GLP-1 side effects by medication
Mounjaro
Zepbound
- Zepbound Side Effects
- Does Zepbound Make You Tired?
- Does Zepbound Cause Hair Loss?
- Does Zepbound Cause Diarrhea?
- Does Zepbound Cause Headaches?
- Does Zepbound Cause Constipation?
- Zepbound Injection Site Reactions
- Zepbound Heartburn & Acid Reflux
- Zepbound Long-Term Side Effects: What 3+ Years of Data Show
- Zepbound Nausea
Wegovy
Ozempic
Tirzepatide
- Does Tirzepatide Make You Tired? Fatigue on Compounded Tirzepatide
- Tirzepatide Hair Loss: What Happens on Compounded Tirzepatide
- Tirzepatide Diarrhea: What to Expect on Compounded Tirzepatide
- Tirzepatide Constipation: What to Expect on Compounded Tirzepatide
- Tirzepatide Headaches: What to Know on Compounded Tirzepatide
- Tirzepatide Injection Site Reactions: Vials, Syringes & What's Normal