Key Takeaways: Wegovy Side Effects

Most common: nausea, vomiting, diarrhoea, constipation, stomach pain, headache, fatigue (affect >1 in 10).
When they start: usually within first few days after a dose, especially after increasing the dose.
How long they last: typically improve within days to weeks as your body adjusts; may persist longer in some.
Serious side effects: pancreatitis, gallbladder disease, severe allergic reactions, diabetic retinopathy complications – seek urgent help.
Contraindications: medullary thyroid cancer (personal/family), MEN2, pregnancy, breastfeeding, allergy.
Food interactions: none direct, but delayed stomach emptying may affect absorption of oral medicines.

Wegovy is a highly effective weight‑loss medication, but like all medicines, it can cause side effects. Knowing what to expect, when they might happen, and how long they last helps you manage them safely. This guide covers everything from common reactions to serious warnings.

Important Medical Advice

Seek immediate medical help if you experience: severe pain in stomach area (may move to your back) – could be pancreatitis; swelling of face, lips, tongue or throat – severe allergic reaction; changes in vision – diabetic retinopathy; or signs of gallstones (severe pain, jaundice). Also seek help for an erection lasting >4 hours (priapism) though rare.

What Are the Common Side Effects of Wegovy?

Based on clinical trials and the Patient Information Leaflet, side effects are grouped by frequency:

Very common (affect more than 1 in 10 people)

Nausea (feeling sick)
Vomiting (being sick)
Diarrhoea
Constipation
Stomach pain
Headache
Fatigue (feeling weak or tired)

Common (affect up to 1 in 10)

Dizziness, indigestion, burping, gas (flatulence), bloating
Inflammation of stomach (gastritis) – signs include stomach ache, nausea
Reflux or heartburn (gastro‑oesophageal reflux disease)
Gallstones, hair loss, injection site reactions
Change in taste, change in skin sensation
Low blood sugar (hypoglycaemia) – mainly in people with diabetes

Most of these are mild to moderate and tend to lessen over time.

When Do Wegovy Side Effects Start?

Side effects usually appear soon after you start treatment or after a dose increase. Because Wegovy is started at a low dose and increased every 4 weeks, many people notice symptoms like nausea in the first few days after an injection, especially when moving to a higher strength.

First injection: Some feel mild nausea within hours to a day.
After dose escalation: Symptoms may reappear or worsen for a few days as your body adapts to the new level.
Gastrointestinal effects: Typically start within 24–48 hours after injection.

If side effects are severe or persistent, contact your doctor – they may adjust your dose schedule.

How Long Do Wegovy Side Effects Last?

Most side effects are temporary and improve as your body gets used to the medicine. Duration varies:

Acute nausea/vomiting: Often lasts a few days after each dose increase, then subsides.
Mild GI symptoms: May persist for several weeks but usually become less bothersome.
Fatigue or headache: Often resolve within the first month.
Injection site reactions: Usually mild and clear within a few days.

If side effects do not improve after 4 weeks on the same dose, or if they are intolerable, speak to your doctor.

Wegovy Side Effects Timeline (Onset & Duration)

Time period	Typical side effect pattern
First 1–3 days after injection	Nausea, vomiting, diarrhoea may peak. Often mild.
Weeks 1–4 (0.25 mg)	Body adapts; symptoms usually improve by week 4.
After each dose increase	Brief return of GI symptoms for a few days, then settle.
Maintenance phase (2.4 mg)	Most people have minimal or well‑tolerated side effects.
Long‑term (>6 months)	Side effects generally mild; monitor for gallstones, pancreatitis (rare).

Everyone responds differently – some have few side effects, while others may need a slower dose titration.

Who Should Not Use Wegovy? (Contraindications)

Wegovy is not suitable for everyone. Do not use if any of the following apply:

Allergy to semaglutide or any excipients (disodium phosphate, propylene glycol, phenol).
Personal or family history of medullary thyroid carcinoma (MTC) or Multiple Endocrine Neoplasia syndrome type 2 (MEN 2).
Pregnancy or breastfeeding – see special conditions below.
Severe kidney disease (eGFR <15 mL/min) – no data, not recommended.
Simultaneous use of other GLP‑1 receptor agonists (e.g. liraglutide, dulaglutide).

If you have a history of pancreatitis, diabetic retinopathy, or gallbladder problems, discuss carefully with your doctor.

Food and Drug Interactions with Wegovy

Food interactions

Wegovy is injected, so food does not affect its absorption. However, because it delays stomach emptying, it may affect how quickly some oral medications are absorbed. This is usually not clinically significant, but for certain medicines (e.g., levothyroxine, some antibiotics) your doctor may advise taking them at a consistent time relative to your Wegovy injection.

Drug interactions

Other GLP‑1 agonists: Do not use together (risk of additive side effects).
Insulin or sulfonylureas: Increased risk of hypoglycaemia – your doctor may adjust doses.
Oral contraceptives: No known interaction, but delayed gastric emptying could theoretically affect absorption – consider an additional barrier method if you have severe GI symptoms.
Warfarin: Monitor INR more frequently when starting or stopping Wegovy.

Always tell your doctor about all medicines you take, including herbal products.

Wegovy Side Effects FAQs

What are the most common side effects of Wegovy?

Nausea, vomiting, diarrhoea, constipation, stomach pain, headache, and fatigue affect more than 1 in 10 people. Most are mild and improve over time.

When do Wegovy side effects usually start?

They often begin within the first few days after the first injection or after a dose increase. GI symptoms like nausea can appear within 24 hours.

How long do Wegovy side effects last?

Most side effects improve within days to weeks as your body adjusts. Some may persist longer but usually become milder. If they don’t improve, tell your doctor.

Can I drink alcohol while on Wegovy?

Moderate alcohol is not known to directly interact, but it may worsen nausea or increase the risk of low blood sugar if you also take diabetes medication.

Who should not use Wegovy?

Do not use if you have a personal/family history of medullary thyroid cancer, MEN2, are pregnant/breastfeeding, or allergic to semaglutide.

Managing Side Effects with Professional Support

If you’re experiencing side effects or have concerns about starting Wegovy, a UK‑registered doctor can help. Through an online consultation, you can discuss your symptoms and get advice on managing them.