Weight loss drug side effects compared: nausea, GI issues, and quit rates
Last reviewed: September 2026·Based on 3 clinical trials
Nausea is the #1 reason people worry about starting weight loss medication — and the #1 reason some people stop. Here is exactly how the three newest drugs compare, using data from their largest studies.
93%
stayed on semaglutide
(7% quit from side effects)
94%
stayed on tirzepatide
(6% quit from side effects)
92%
stayed on orforglipron
(8% quit from side effects)
Side-by-side: how the three drugs compare
Each percentage below represents the share of people who experienced that side effect at any point during the study. Higher bars mean more people were affected.
Nausea
semaglutide44%
tirzepatide31%
orforglipron33%
Vomiting
semaglutide24%
tirzepatide18%
orforglipron19%
Diarrhoea
semaglutide30%
tirzepatide23%
orforglipron15%
Constipation
semaglutide24%
tirzepatide12%
orforglipron18%
Fatigue
semaglutide11%
tirzepatide7%
orforglipron6%
Indigestion
semaglutide9%
tirzepatide10%
orforglipron10%
✓ Zepbound: 31% nausea in trials✓ Foundayo: 15% diarrhoea in trials✓ Zepbound: 6% quit rate in trials
Key insight
In these studies, tirzepatide (Zepbound) showed 31% nausea, 18% vomiting, and 23% diarrhoea. Orforglipron (Foundayo) showed 33% nausea and 19% vomiting — within 1–2 percentage points of tirzepatide — and 15% diarrhoea. Semaglutide (Wegovy) showed 44% nausea and 30% diarrhoea in its trial.
When do side effects peak? A typical timeline
Side effects are not constant. They follow a predictable pattern tied to dose increases:
Weeks 1–2
Starting dose — mildest
Most people start at the lowest dose. Nausea affects roughly 1 in 3 people, usually mild. The body is adjusting.
Weeks 3–8
Dose increases — worst window
Each dose increase can trigger a new wave of nausea. This is the period when most people feel the worst. It usually passes within 3–5 days per increase.
Weeks 8–16
Settling down
For most people, stomach side effects become significantly milder or disappear entirely as the body adapts to the maintenance dose.
Week 16+
Maintenance — steady state
The majority of people who stayed through the adjustment period report minimal or no ongoing stomach issues.
How to reduce side effects
Eat smaller, more frequent meals
Large meals overwhelm a slower-emptying stomach. 4–5 small meals instead of 2–3 large ones makes a significant difference.
Avoid fatty and fried foods
High-fat meals sit in the stomach longer and are the most common nausea trigger. Lean protein and vegetables are easier to tolerate.
Eat slowly
Eating too fast before your brain registers fullness is the top cause of post-meal nausea. Take 20+ minutes per meal.
Stay hydrated
Sip water throughout the day. Dehydration worsens nausea and is common when appetite is reduced and you are eating less food.
Consistent timing
Take your medication at the same time each week (injections) or day (pills). Consistency helps the body adapt.
Slow titration
Stay at each dose for the full 4 weeks before increasing. If side effects are severe, your doctor can extend the titration period.
Full side effect profiles
Wegovy (semaglutide)
Weekly injection
STEP 1 · 1,961 participants
Nausea44%
Vomiting24%
Diarrhoea30%
Constipation24%
Abdominal pain20%
Fatigue11%
Indigestion9%
Stayed on medication93%
Quit due to side effects7%
Zepbound (tirzepatide)
Weekly injection
SURMOUNT-1 · 2,539 participants
Nausea31%
Vomiting18%
Diarrhoea23%
Constipation12%
Abdominal pain9%
Fatigue7%
Indigestion10%
Stayed on medication94%
Quit due to side effects6%
Foundayo (orforglipron)
Daily pill
ATTAIN-1 · 989 participants
Nausea33%
Vomiting19%
Diarrhoea15%
Constipation18%
Fatigue6%
Indigestion10%
Stayed on medication92%
Quit due to side effects8%
Bottom line
In studies, tirzepatide (Zepbound) showed 31% nausea, 23% diarrhoea, and a 6% quit rate. Orforglipron (Foundayo) showed 33% nausea and 15% diarrhoea, with an 8% quit rate. Semaglutide (Wegovy) showed 44% nausea and 30% diarrhoea, though over 93% of people still stayed on medication. For all three drugs, side effects typically peak during dose increases and resolve by weeks 12–16.
In their own trials: tirzepatide (Zepbound) showed 31% nausea (vs 44% semaglutide, 33% orforglipron), 18% vomiting (vs 24% and 19%), and a 6% quit rate. Individual results vary.
Nausea is the most common side effect, affecting 31–44% of people in studies. However, it is usually mild to moderate, peaks during dose increases, and subsides within a few weeks for most people. About 6–8% of people quit due to side effects — meaning over 90% found them manageable.
Semaglutide (Wegovy) has a higher nausea rate: 44% vs 31% for tirzepatide (Zepbound). Semaglutide also has higher rates of vomiting (24% vs 18%) and diarrhea (30% vs 23%). This is consistent across multiple trials.
The most common side effects in the ATTAIN-1 trial were: nausea (33%), vomiting (19%), constipation (18%), diarrhea (15%), and indigestion (10%).
Yes. Most stomach side effects peak during the first few weeks, especially around dose increases. The data shows that by weeks 12–16, the majority of people experience significantly reduced or no stomach symptoms as the body adapts to the medication.
In their own trials, tirzepatide showed a 6% quit rate with 94% of people in the SURMOUNT-1 trial staying on medication through the full trial, alongside a 31% nausea rate. Orforglipron showed an 8% quit rate with 33% nausea, and semaglutide showed a 7% quit rate with 44% nausea. Individual responses vary.
Yes. Eating smaller meals, avoiding fatty or spicy foods, eating slowly, staying hydrated, and taking the medication at a consistent time all help. Slow titration (staying at each dose level for 4 weeks before increasing) also reduces side effects. If nausea is severe, your doctor may slow the dose increase schedule.
Written and maintained by one person · Built with agentic AI tools · Every number checked against the cited trial · Not medical advice
STEP 1 — Semaglutide (injection): 1,961 adults with obesity or overweight with comorbidities, no type 2 diabetes, 68 weeks. New England Journal of Medicine, 2021. View source ↗
SURMOUNT-1 — Tirzepatide: 2,539 adults with obesity or overweight with comorbidities, no type 2 diabetes, 72 weeks. New England Journal of Medicine, 2022. View source ↗
ATTAIN-1 — Orforglipron: 3,127 adults with obesity or overweight with comorbidities, no type 2 diabetes, 72 weeks. New England Journal of Medicine, 2025. View source ↗
Built with agentic AI tools and not a substitute for medical advice
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