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Trial-sourced incidence data

Wegovy side effects

Wegovy (semaglutide) has 6 documented side effects from peer-reviewed Phase 3 trial data. This page covers how common each one is, when they start and stop, how to manage them, and the warning signs that mean you should call a doctor — every figure sourced to trial data or the FDA label.

When Wegovy side effects start, peak, and resolve

Incidence is from Wegovy trial data. Onset, peak, and resolution weeks are typical GLP-1-class patterns — individual timing varies with how fast your dose is escalated.

Wegovy side effects with trial incidence and typical onset, peak, and resolution week.
Side effectIncidenceStartsPeaksUsually resolves
Nausea44.2%wk 1wk 4wk 12
Diarrhea31.5%wk 2wk 6wk 14
Vomiting24.8%wk 2wk 5wk 10
Constipation23.4%wk 3wk 8wk 24
Fatigue11%wk 1wk 3wk 8

“Resolves” = the week by which most patients on a stable dose no longer report the symptom. A new dose increase can restart the clock briefly.

How to manage the most common ones

Nausea

44.2% of trial patients

GLP-1 medications slow gastric emptying — food stays in your stomach longer, which triggers fullness signals and, for some people, a queasy feeling. The same mechanism is what helps with weight loss and blood sugar.

Manage at home

  • Eat smaller meals more often — 4–6 small meals beats 3 large ones.
  • Avoid high-fat, greasy, or fried foods on injection day and the day after.
  • Hydrate steadily (small sips) — sudden large volumes can worsen the feeling.
  • Ginger (tea, candies, capsules) is the best-studied OTC remedy.

Call your prescriber if

  • Nausea so severe you cannot keep water down for 24 hours (risk of dehydration / acute kidney injury).
  • Persistent vomiting beyond 48 hours.
  • Severe abdominal pain — could signal pancreatitis (rare but serious; discontinue medication and seek care).
Full nausea guide

Diarrhea

31.5% of trial patients

GLP-1 medications change gut motility unpredictably — for some people the result is faster small-bowel transit (diarrhea), for others slower colonic transit (constipation). Many people swing between the two during titration.

Manage at home

  • Hydrate aggressively — water plus electrolyte drinks to replace lost sodium and potassium.
  • BRAT diet (bananas, rice, applesauce, toast) for 24–48 hours if symptoms flare.
  • Avoid dairy, caffeine, alcohol, and high-fat foods during a flare.
  • OTC loperamide (Imodium) is generally safe; use lowest effective dose.

Call your prescriber if

  • Diarrhea more than 6 times in 24 hours or lasting beyond 48 hours.
  • Blood in stool or black/tarry stools.
  • Signs of dehydration: dizziness, low urine output, racing pulse.
Full diarrhea guide

Vomiting

24.8% of trial patients

Same mechanism as nausea — slowed gastric emptying plus enhanced fullness signaling. Vomiting tends to follow a high-fat or large meal during the peak-nausea window.

Manage at home

  • Switch to clear liquids (broth, electrolyte drinks, weak tea) until vomiting stops.
  • Resume eating with bland low-fat foods — crackers, rice, toast, applesauce.
  • Inject in the evening so you sleep through the peak; eat sparingly the next day.
  • Avoid lying flat after eating — sit upright for 30–60 minutes.

Call your prescriber if

  • Cannot keep liquids down for 24 hours.
  • Severe abdominal pain, especially upper-abdominal (possible pancreatitis).
  • Signs of dehydration: dizziness, dark urine, racing pulse.
Full vomiting guide

Constipation

23.4% of trial patients

GLP-1 drugs slow gastric emptying and colonic transit time. Combined with smaller portions, lower fluid intake, and a reduced fiber load, you get harder, less frequent stools.

Manage at home

  • Increase fiber to 25–35 g/day from whole foods first (chia, ground flaxseed, oats, berries, leafy greens).
  • Drink at least 2L of water daily — fiber without water makes constipation worse.
  • Walk 20–30 minutes most days — gentle movement promotes bowel motility.
  • Magnesium citrate (200–400 mg in the evening) is the most-recommended OTC option.

Call your prescriber if

  • No bowel movement for more than 5 days.
  • Severe abdominal pain, distension, or vomiting (possible obstruction or ileus).
  • Blood in stool.
Full constipation guide

Headache

14.6% of trial patients

Reduced food intake means less fluid, less carbohydrate, and sometimes electrolyte shifts. Headaches usually trace back to hydration or skipped meals rather than the medication directly.

Manage at home

  • Hydrate consistently — 2L+ of water daily, more if you exercise.
  • Don't skip meals even when you're not hungry — small frequent intake stabilizes blood sugar.
  • Add electrolytes (sodium, potassium, magnesium) if you sweat heavily or notice fatigue.
  • OTC analgesics (acetaminophen, ibuprofen) are fine for occasional use.

Call your prescriber if

  • Sudden severe headache ("worst of your life").
  • Headache with vision changes, weakness, or confusion.
  • Persistent daily headache beyond 2 weeks despite hydration and steady meals.
Full headache guide

Fatigue

11% of trial patients

GLP-1 drugs suppress appetite — if you eat well below your maintenance energy needs you'll feel tired. Adequate protein, electrolytes, and a modest deficit (not extreme) prevent the worst of it.

Manage at home

  • Target 0.7–1.0 g of protein per pound of goal body weight daily — protects against muscle loss and energy crashes.
  • Don't skip meals — aim for 3 modest meals plus 1–2 snacks rather than 1 large dinner.
  • Sodium + potassium replacement if you sweat heavily (low-carb-style electrolytes).
  • Walk 20–30 minutes daily — counterintuitively, light activity reduces fatigue more than rest.

Call your prescriber if

  • Severe fatigue affecting daily function for more than 2 weeks.
  • Fatigue with palpitations, chest pain, or fainting.
  • Fatigue with very low fasting glucose readings (especially if you take insulin or sulfonylureas).
Full fatigue guide

Every documented Wegovy side effect

Sorted by trial incidence. Click any effect for a full patient-facing deep dive.

Frequently asked

How long do Wegovy side effects last?

Most Wegovy side effects — especially gastrointestinal — are dose-related and subside within 2-4 weeks at each dose level. Nausea, the most common, peaks around week 4 and usually resolves by week 12 on a stable dose. Constipation is the most persistent.

What is the worst week for Wegovy side effects?

The first 1-2 weeks after each dose increase, when your gut adjusts to the higher dose. The roughest stretch is usually the first month and briefly after each titration step. If a symptom stops you eating or drinking, ask your prescriber to hold the dose longer.

Do Wegovy side effects go away?

For most people, yes — the common GI effects fade as the body adapts, usually within 2-4 weeks of a stable dose. Serious effects (severe abdominal pain, pancreatitis or gallbladder signs, vision changes) are not adjustment symptoms and need prompt care.

How do I reduce Wegovy nausea?

Smaller meals, stop at first fullness, avoid fried/high-fat food, hydrate, don't lie down right after eating. Slower dose escalation is the strongest lever — ask your prescriber to hold a step. Ginger and B6 help some. Vomiting that prevents fluids needs a same-day call.

Incidence rates from peer-reviewed pivotal-trial publications and FDA prescribing information. Individual experience varies — discuss any new symptoms with your prescriber. Medically reviewed by Jane Novak, MD, MPH.