Wegovy Side Effects: How Common, How Long, How Serious

Most writing about Wegovy side effects tells you they are usually mild and usually temporary. Both are true. Neither tells you how long "temporary" is, and that is the question people are actually asking. The pooled trial data answers it in days, and one side effect behaves nothing like the others.

Key takeaways#

• 73% of people on Wegovy report a gastrointestinal side effect, and 4.3% stop taking it because of one. Those two numbers are usually quoted apart, and together they are the whole story.
• Median duration: nausea 8 days, diarrhoea 3 days, vomiting 2 days. Individual episodes are short.
• Constipation is the exception at a median of 47 days, roughly six times longer than nausea, and its prevalence plateaus rather than declining.
• Side effects concentrate during dose escalation and taper after roughly week 20, which is when the 2.4 mg maintenance dose is reached.
• Hair loss is on the FDA label as a reaction occurring in 5% or more of patients. It is neither a myth nor a sign something has gone wrong.

Wegovy and Ozempic are the same molecule at different doses#

Both are semaglutide. Ozempic is licensed for type 2 diabetes at up to 2 mg weekly; Wegovy is licensed for weight management at 2.4 mg weekly. The side-effect profile is the same family of effects, and the higher maintenance dose is why the weight-management trials report them more often.

That matters for searching. Most published "Ozempic side effects" data at weight-management doses is in fact Wegovy trial data, because that is where the 2.4 mg evidence was generated. Klarovel covers the brand split separately in Ozempic versus Wegovy.

One Norwegian note: Ozempic is not a weight-loss option here. It is licensed for type 2 diabetes, and Wegovy is the semaglutide product marketed for weight management.

How often each side effect actually occurs#

From the Wegovy prescribing information, pooled across the adult weight-management trials. N = 2,116 on Wegovy 2.4 mg against 1,261 on placebo.

Read the last two rows together. Nearly three quarters of people report something, and about one in twenty-five reports it as severe. Research has shown 99.5% of these events were non-serious and 98.1% mild to moderate.

Beyond the gut, the label lists abdominal pain, headache, fatigue, dyspepsia, dizziness, bloating, belching, flatulence, reflux, gastroenteritis and hair loss among reactions occurring in 5% or more of patients.

How long they last, which is the part usually left out#

This is the number that answers the question most people came with. From a pooled analysis of STEP 1 to 3:

Constipation is the outlier and it is not close. Nausea resolves in about a week. Constipation runs closer to seven weeks, and while the prevalence of nausea, diarrhoea and vomiting peaks around week 20 and then falls, constipation plateaus around week 10 and stays. Studies have shown this is consistent with the way GLP-1 receptor agonists slow gastric motility, which is also part of how the drug works.

The practical reading: if you are three weeks in and still nauseated every day, that is outside the median and worth raising with a prescriber. If you are constipated at week six, that is squarely within what the trials describe.

Who actually stops taking it#

Reported rates of "side effects" sound alarming until you look at how many people they drive off the drug.

• 6.8% discontinued for any adverse reaction, against 3.2% on placebo.
• 4.3% discontinued specifically for a gastrointestinal reaction, against 0.7% on placebo.
• The individual drivers were nausea (1.8%), vomiting (1.2%) and diarrhoea (0.7%).
• A further 12.5% reduced the dose or paused temporarily rather than stopping.

So 73% feel something, about 1 in 8 adjusts the dose, and about 1 in 23 stops. Most discontinuations happened during escalation rather than at the maintenance dose.

Worth one caveat on generalising those figures. In the much larger and longer SELECT cardiovascular trial, which ran 17,604 patients with existing cardiovascular disease, discontinuation for adverse events was 16.6% against 8.2% on placebo. An older, sicker population on the same drug stopped it far more often, and the weight-management trial figures should not be read as the ceiling.

The three that are not gastrointestinal#

Hair loss is on the label. It appears among reactions occurring in 5% or more of patients. Rapid weight loss from any cause is associated with telogen effluvium, a shedding phase that typically reverses, so the mechanism is not necessarily the drug acting on hair directly. Either way, someone searching whether semaglutide causes hair loss deserves the straight answer: it is a labelled reaction, not a rumour.

Gallbladder disease is more common, and not only because of the weight loss. Cholelithiasis was reported by 1.6% of Wegovy-treated adults against 0.7% on placebo, and cholecystitis by 0.6% against 0.2%. The label makes a point that is easy to miss: the excess held even after accounting for the degree of weight loss. Rapid weight loss alone does not explain it.

Alcohol is not a labelled interaction, and that is not the same as no effect. There is no contraindication, but many people report reduced desire for alcohol on GLP-1 receptor agonists, and that observation is now itself under study. Alcohol is also a gastric irritant, which is unlikely to help during escalation.

What the numbers add up to#

Wegovy's side-effect profile is common, mostly short-lived, concentrated in the escalation window, and severe in a small minority. The figure worth carrying is not 73% and not 4.3% alone, but the distance between them: most people feel something, most of it passes within days, and few people stop.

The two facts that surprise readers are that constipation behaves completely differently from the rest, and that hair loss is a labelled reaction. Both are in the primary sources and neither is widely reported.

For the dosing schedule these effects track against, see the Wegovy complete guide and its titration chart. For how semaglutide compares with the rest of the class, see peptides for weight loss. Complete the Klarovel questionnaire to see what the engine recommends from a full health profile rather than from a side-effect list.