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Semaglutide side effects
Semaglutide is the medicine in Wegovy pens and Wegovy tablets. Nausea is the side effect people report most, and the slow dose schedule exists to keep nausea in check.
By Gary Atmos, Penzilla Editorial Team. Last reviewed 8 October 2026.
Side effects ranked by frequency
- Most frequent (over 1 person in 10): nausea, diarrhoea, vomiting, constipation, stomach ache, headache, fatigue.
- Common (up to 1 in 10): dizziness, indigestion, stomach lining inflammation, heartburn, bloating, burping, wind, gallstones, hair thinning, soreness where you inject, low blood sugar for people with type 2 diabetes.
- Uncommon (up to 1 in 100): acute pancreatitis, faster heart rate, slowed stomach emptying.
Frequencies come from the product licence.
Numbers from STEP 1
- Nausea: 44 in 100 on semaglutide, 17 in 100 on placebo
- Diarrhoea: 32 in 100 against 16 in 100
- Stopped treatment because of stomach effects: 4.5 in 100 against 0.8 in 100
Pancreatitis: the January 2026 warning
On 29 January 2026 the MHRA tightened pancreatitis warnings across the GLP-1 family, semaglutide included.
Red flag. Strong, lasting stomach pain, sometimes reaching through to your back, needs same day medical attention. The MHRA names this as the main warning sign of pancreatitis. Tell the MHRA about any suspected reaction on the Yellow Card site.
Easing stomach side effects
Smaller portions help most. Eat slowly and stop at the first sign of fullness. Go easy on rich, greasy food in the week after an increase. Keep fluids up. If a new dose hits hard, ask the prescriber about staying put for another four weeks.
Gallstones and fast weight loss
Rapid weight loss of any kind raises the chance of gallstones. Pain under the right ribs, especially after eating, deserves a call to your GP.
Eyes and diabetes
People with diabetic eye disease need monitoring, because a fast drop in blood sugar can affect the retina. Mention any eye condition at the consultation.
Pen and tablets share the list
The tablets carry the same medicine through the stomach, so the same effects apply. Wegovy tablets.
Planning a pregnancy
The licence says to stop semaglutide at least two months beforehand. Do not use Wegovy while pregnant or breastfeeding.
Wegovy prices. Wegovy or Mounjaro?
Questions people ask
What is the most common side effect of semaglutide?
Nausea. In STEP 1, 44 in 100 people reported nausea.
How long does Wegovy nausea last?
Usually days to a few weeks after each increase.
Does semaglutide cause hair loss?
The licence lists hair loss as common, meaning up to 1 person in 10.
Does Wegovy cause gallstones?
Gallstones are listed as a common side effect, and rapid weight loss itself raises the risk.
Sources
- Novo Nordisk, Wegovy Summary of Product Characteristics (electronic medicines compendium)
- Wilding JPH and colleagues, STEP 1, New England Journal of Medicine, 2021
- MHRA Drug Safety Update, GLP-1 and dual GLP-1/GIP receptor agonists: strengthened warnings on acute pancreatitis, 29 January 2026
- MHRA, Yellow Card reporting site
