Most Wegovy side effects are gastrointestinal — nausea, diarrhoea, vomiting, constipation and abdominal pain are the most commonly reported, affecting a substantial proportion of people, particularly during dose increases, and tend to be mild to moderate and improve over time. Around 4 in 10 people report nausea at some point during treatment, though far fewer experience it as severe. Less common side effects include headache, fatigue, dizziness and injection site reactions. Serious side effects — including pancreatitis, gallbladder problems, kidney injury and severe allergic reactions — are rare but require prompt medical attention. Around 1 in 20 people stop treatment due to side effects, most commonly gastrointestinal ones.
Wegovy works by mimicking GLP-1, a hormone that slows how quickly your stomach empties and increases feelings of fullness. That slower digestion is central to how the medicine helps you eat less — but it's also the direct cause of most side effects, since a stomach that empties more slowly is more prone to nausea, bloating and changes in bowel habits, particularly while your body adjusts to a new or higher dose. Understanding this connection helps explain why side effects and effectiveness are, to some extent, two sides of the same mechanism.
Common Side Effects and How to Manage Them| Side effect | Practical management |
|---|---|
| Nausea | Eat smaller, more frequent meals; avoid high-fat or greasy food, particularly after a dose increase; eat slowly and stop before feeling overly full |
| Diarrhoea | Stay well hydrated; plain, low-fibre foods can help in the short term; contact your prescriber if it's severe or persistent |
| Constipation | Increase fibre gradually through fruit, vegetables and wholegrains; drink water consistently through the day; gentle regular movement can help |
| Vomiting | Sip fluids slowly to avoid dehydration; contact your prescriber if you can't keep fluids down or it continues beyond a day or two |
| Abdominal pain | Mild discomfort is common, particularly early on; contact your prescriber if pain is severe, persistent, or accompanied by other symptoms |
| Headache | Usually mild and temporary; stay hydrated and speak to your pharmacist if it persists or is severe |
For more detail on eating well while your appetite changes, including how to manage nausea through food choices, see our nutrition guide covering GLP-1 treatments.
Less Common Side EffectsBeyond the core gastrointestinal symptoms, Wegovy's trial programme also reported fatigue, dizziness, changes in taste, gas, and injection site reactions (redness, itching or swelling at the injection site, usually mild and temporary). Hair thinning has also been reported, generally linked to the physiological stress of rapid weight loss itself rather than a direct effect of the medicine — see our nutrition guide for how adequate protein intake can support hair health during treatment.
Injection Site ReactionsMild redness, itching, swelling or a small lump at the injection site is fairly common and usually resolves on its own within a few days. Rotating your injection site each week — rather than injecting in the same exact spot repeatedly — helps reduce how often this happens; see our step-by-step injection guide for the full technique. Contact your prescriber if a reaction is severe, spreads, or doesn't improve after a few days.
Serious side effects are uncommon but require prompt attention. Contact NHS 111 urgently, or your prescriber, if you experience:
- Severe or persistent stomach problems
- Symptoms of acute pancreatitis, including severe abdominal pain that may spread to your back, sometimes with vomiting
- Signs of gallbladder problems, such as pain in the upper right abdomen, fever, or yellowing of the skin or eyes
- Signs of dehydration that could affect your kidneys, such as reduced urination, dizziness or confusion
- A severe allergic reaction, including swelling of the face, lips, tongue or throat, or difficulty breathing
- A neck lump or swelling, hoarseness, trouble swallowing or shortness of breath
- Sudden vision changes
For emergencies, call 999 immediately. You can also report any suspected side effect to the MHRA via the Yellow Card scheme at yellowcard.mhra.gov.uk.
Important
Wegovy's UK prescribing information includes a warning about thyroid C-cell tumours observed in animal studies, and it isn't recommended for anyone with a personal or family history of medullary thyroid carcinoma or Multiple Endocrine Neoplasia syndrome type 2. Always disclose your full medical and family history during your consultation.
Side effects tend to follow a predictable pattern: most noticeable in the days following a dose increase, then gradually easing as your body adjusts before the next step. This is exactly why Wegovy follows a gradual titration schedule rather than starting at the full dose — see our dedicated Wegovy dose schedule guide for the complete timeline. If a particular dose is proving difficult, the standard approach is to stay at that dose for longer than the minimum before increasing further, rather than pushing through significant discomfort.
Worth knowing
Roughly 1 in 20 people in Wegovy's clinical trials stopped treatment because of side effects, most commonly gastrointestinal ones. This doesn't mean side effects are inevitable or unmanageable for everyone — the majority of people who experience them find they ease with time, and open communication with your prescriber about pacing your titration can make a genuine difference.
Wegovy's side-effect profile is broadly similar to other GLP-1 medicines, including Mounjaro and the Wegovy pill, since all work through overlapping appetite-regulating pathways. Some people find Mounjaro's dual GIP/GLP-1 mechanism produces slightly more pronounced early gastrointestinal effects, though individual tolerance varies considerably and current evidence doesn't clearly establish one medicine as consistently better tolerated than another across the board.
Because side effects tend to cluster around dose increases, it helps to have a general strategy for the first few days after each step up. Many people find it useful to plan lighter, blander meals for the two or three days following an increase, avoid scheduling anything too physically demanding immediately afterwards, and keep hydration consistent throughout. This isn't about avoiding the dose increase — it's about making the adjustment period as comfortable as possible while your body catches up.
Tracking Your Side EffectsKeeping a simple note of any side effects you notice — what they were, roughly how severe, and how they related to your last dose change — is genuinely useful, both for your own peace of mind and for your prescriber, who can use that pattern to judge whether your titration pace needs adjusting. This doesn't need to be complicated; a few lines in a notes app after each dose change is enough to spot patterns over time.
Who May Be More Likely to Experience Side Effects- A history of significant gastrointestinal issues, such as gastroparesis or severe reflux, may increase the likelihood or severity of GI side effects
- Rapid dose escalation, or moving up before you've properly adjusted to the previous dose, tends to produce more noticeable side effects
- Dehydration going into treatment can make gastrointestinal side effects, particularly constipation, more pronounced
- Taking other medicines that also affect gut motility may interact with Wegovy's own effect on digestion
Ongoing Support, Not Just a Prescription
Every Happy Pharmacy patient has access to our GPhC-registered pharmacy team throughout treatment — including honest advice on managing side effects as your body adjusts.
Start Your Free Online Consultation → Use code SWITCH10 if you're switching from another providerHappy Pharmacy is a GPhC-registered pharmacy (No. 9012585) — Superintendent Pharmacist: Palvinder Deol — Rated 4.8★ Excellent on Trustpilot
- Wegovy® (semaglutide) UK Summary of Product Characteristics, medicines.org.uk (emc).
- Wilding JPH, et al. Once-Weekly Semaglutide in Adults with Overweight or Obesity (STEP-1). N Engl J Med. 2021.
- Novo Nordisk. Wegovy® Indications & HCP Information, novomedlink.com.
- MHRA. Yellow Card scheme — reporting suspected side effects of medicines.