Wegovy is well studied. The STEP trials enrolled thousands of people, and semaglutide has been in real world use globally since 2017 (as Ozempic) and since 2021 (as Wegovy specifically). The safety profile is reasonably well understood. Most side effects are predictable, manageable, and improve with time. A smaller number are uncommon but serious enough to be on your radar.

The Most Common Side Effects

These affect a majority of people at some point during treatment, usually most strongly in the first month and after dose increases.

Gastrointestinal effects

  • Nausea. The most common. Often described as feeling full or queasy rather than 'about to vomit'. Usually settles within the first month.
  • Vomiting. Less common than nausea but does happen, particularly after large or rich meals.
  • Diarrhoea or constipation. Either can occur. Both usually settle within weeks.
  • Indigestion, reflux, bloating. From the slowed gastric emptying.
  • Abdominal pain. Mild to moderate. Severe persistent pain is a different matter (see pancreatitis below).
  • Belching, gas. Common and usually mild.

Other common effects

  • Reduced appetite (intended effect)
  • Fatigue, particularly in the first month
  • Headache
  • Dizziness
  • Injection site reactions (redness, itching, small bruise)
  • Hair shedding (related to weight loss, not the medication directly)
  • Reduced taste sensitivity
  • Sore throat, runny nose

Managing The Common Side Effects

Most people get through the early weeks with small adjustments rather than stopping. Useful approaches:

  • Smaller meals, eaten more slowly
  • Stop eating when comfortable, not full
  • Reduce fatty, greasy, or heavily processed foods which make nausea worse
  • Stay hydrated, particularly with electrolytes if vomiting or diarrhoea
  • Bland easy to digest foods on injection day if nausea is bad
  • Ginger tea, peppermint tea, or plain biscuits help some people with nausea
  • Anti-nausea medication if the doctor decides it is appropriate

See the side effect management blog post for more detail.

Less Common But Serious Side Effects

Pancreatitis A rare but real risk. Symptoms: severe, persistent abdominal pain, usually in the upper abdomen, often radiating through to the back, often with nausea and vomiting. If this happens, stop Wegovy and seek medical assessment urgently. The medication is contraindicated if you have had previous pancreatitis.

Gallbladder problems

Increased risk of gallstones and gallbladder inflammation, particularly during periods of significant weight loss. Symptoms include upper right abdominal pain (often worse after fatty meals), nausea, sometimes yellowing of the skin or eyes.

Acute kidney injury

Usually secondary to dehydration from severe vomiting or diarrhoea. Maintaining hydration is the protective factor. Pre-existing kidney disease needs monitoring.

Severe allergic reaction

Rare but possible. Difficulty breathing, swelling of the face, lips, or tongue, severe rash. Medical emergency.

Diabetic retinopathy

In people with type 2 diabetes, rapid blood glucose improvement can occasionally worsen existing diabetic eye disease. For people with diabetes and known retinopathy, baseline eye assessment before starting is recommended.

Mental health changes

Postmarketing reports have noted depression and suicidal ideation in a small number of patients. Causality is uncertain. People with significant mental health history should discuss this with the prescribing doctor. If significant mood changes develop during treatment, contact the doctor.

Thyroid C-cell tumours

Observed in rat studies. Relevance to humans is unclear. As a precaution, the medication is contraindicated in people with a personal or family history of medullary thyroid carcinoma or MEN2 syndrome.

When Wegovy Is Not Suitable

Wegovy is contraindicated or used with great caution in:

  • Personal or family history of medullary thyroid carcinoma or MEN2 syndrome
  • Pregnancy or planning to conceive within two months
  • Breastfeeding
  • Active or recent pancreatitis
  • Severe gastrointestinal disease, particularly gastroparesis
  • Active gallbladder disease
  • Severe liver disease (limited data)
  • Severe kidney impairment (eGFR below 30, caution)
  • Type 1 diabetes (Wegovy is not indicated)
  • Active or recent severe eating disorder (case by case)
  • Significant uncontrolled mental health condition (case by case)
  • Severe diabetic retinopathy (caution, eye assessment first)
  • Children under 12 (not approved)

Get A Safe Assessment

An online consultation works through your medical history to confirm Wegovy is safe and appropriate for you.

Start Consultation

Drug Interactions

Oral medications

Semaglutide slows gastric emptying. This means oral medications can be absorbed more slowly. For most medications this does not matter clinically, but a few specifics:

  • Oral contraceptives. Generally not significantly affected by Wegovy. Routine continuation is usually fine, but mention to the prescribing doctor.
  • Narrow therapeutic index drugs (warfarin, levothyroxine, some seizure medications). Worth monitoring more closely.

Insulin and sulfonylureas

Combined use can cause hypoglycaemia. The treating doctor usually reduces the dose of the older medication when starting Wegovy in people with type 2 diabetes.

Alcohol

Not a direct interaction, but heavy drinking increases nausea, dehydration, and pancreatitis risk. Many people find they want less alcohol on Wegovy.

Pregnancy And Contraception

Wegovy is not used in pregnancy. Animal data shows potential fetal harm. Women planning pregnancy should stop the medication at least two months before trying to conceive (the longer half life of semaglutide means a longer washout than Mounjaro).

Effective contraception is recommended for women of childbearing age using Wegovy. Unlike Mounjaro, oral contraceptive absorption is not significantly affected, so standard oral contraception is generally fine.

What To Tell The Consulting Doctor

Before starting, the doctor needs to know about:

  • All current medications, including over the counter and supplements
  • Any history of pancreatitis, gallbladder disease, or thyroid issues
  • Any history of eating disorders
  • Mental health history
  • Pregnancy status or plans
  • Other major medical conditions (kidney, liver, gut, eye)
  • Family history of medullary thyroid cancer or MEN2
  • Recent surgical history

Be straight at the consultation. The doctor cannot make a safe decision without accurate information.

Related Reading

Frequently Asked

Nausea, vomiting, diarrhoea, constipation, abdominal pain, indigestion, fatigue, headache, dizziness, and injection site reactions. Gastrointestinal effects dominate and tend to be worst in the first month and after each dose increase.

It is a rare but recognised risk. Severe persistent abdominal pain, often radiating to the back, warrants urgent assessment and stopping the medication until investigated.

In rat studies, semaglutide caused C-cell tumours. The relevance to humans is unclear and no causal link has been established in human use. The medication is contraindicated in people with personal or family history of medullary thyroid carcinoma or MEN2 syndrome.

Postmarketing reports have noted depression and suicidal ideation in a small number of patients on semaglutide. The causality is uncertain. People with significant mental health history should discuss this with the prescribing doctor before starting.

Light to moderate drinking is generally fine. Heavy drinking can increase nausea, dehydration, and pancreatitis risk. Many people find tolerance for alcohol decreases on Wegovy.