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What to Expect

What side effects are normal, and what means STOP NOW?

Updated 2026-05-02

On GLP-1s, nausea, diarrhea, vomiting, and constipation are the most common side effects. They usually show up during dose escalation and get better once you settle at a stable dose. In the STEP 1 trial for semaglutide, 44% had nausea, 24% had vomiting, 30% had diarrhea, 24% had constipation. Most cases were mild to moderate. STOP NOW and seek care for severe persistent belly pain, upper-right belly pain with fever or yellowing skin, severe dehydration, or trouble breathing with hives or face swelling.

IfIf you have mild nausea during escalation
Thenthen eat smaller meals, avoid greasy and spicy food, stay hydrated - this is expected
IfIf you have severe belly pain that doesn't resolve within an hour
Thenthen go to the ER - possible pancreatitis
IfIf you have upper-right belly pain with fever
Thenthen go to urgent care - possible gallbladder disease
IfIf you become severely dehydrated
Thenthen stop injecting until rehydrated and call your prescriber
IfIf you have trouble breathing, hives, or face/lip swelling
Thenthen call 911 - allergic reaction
Key facts
  • STEP 1 nausea: 44% on semaglutide vs placebo; vomiting 24%; diarrhea 30%; constipation 24%
  • Hair loss: 3% on semaglutide vs 1% placebo (see hair loss FAQ)
  • Most side effects resolve within weeks of reaching a stable dose
  • Pancreatitis: 0.2 to 0.3% on STEP 1; below 0.1% on SURMOUNT-1 (not clearly drug-related per investigators)
  • Gallbladder disorders: 1.63x increased risk with semaglutide in pooled analysis; 2.59x for cholelithiasis
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