Side Effects of Ozempic, Wegovy, Zepbound and Mounjaro, Week by Week

The most common side effects of semaglutide (Ozempic, Wegovy) and tirzepatide (Zepbound, Mounjaro) are digestive: nausea, diarrhea, vomiting and constipation^[1,2,3,4]. According to the US labels, most nausea, vomiting and diarrhea shows up while the dose is being stepped up, and it decreases over time^[2,4]. Most of these effects are mild or moderate^[7,8] and, except for constipation, each episode is short: in the Wegovy trials, the median episode lasted 8 days for nausea and 47 for constipation^[5]. Less common effects worth knowing include pancreatitis and gallbladder problems, and a few signs mean calling your doctor without waiting.Dotted underline: a drug-label fact; hover over it to see the date it was checked.

I built this guide from the current US prescribing information on DailyMed for Wegovy, Zepbound, Ozempic and Mounjaro, the EU Wegovy label (the only one that says how long each side effect lasts) and the pooled STEP and SURMOUNT analyses. Ozempic (type 2 diabetes) and Wegovy (weight management, at higher doses) are both semaglutide^[1,3]; Mounjaro (type 2 diabetes) and Zepbound (weight management and obstructive sleep apnea) are both tirzepatide^[2,4]. My semaglutide guide and tirzepatide guide cover each medicine in full; here I lead with the Wegovy and Zepbound figures, from placebo-controlled weight-management trials.

The most common side effects, in numbers

Wegovy figures come from Table 3 of its US label (injection site reactions from the text of section 6.1): three placebo-controlled trials with 2,116 adults treated for up to 68 weeks^[1]. Zepbound figures come from Table 1 of its US label: SURMOUNT-1 and -2, in adults with and without type 2 diabetes, for up to 72 weeks^[2]. This is not a comparison between drugs: both US labels warn that rates from one drug’s trials can’t be directly compared with another’s^[1,2].

Overall, 73% of people on Wegovy and 47% on placebo reported some digestive side effect^[1], as did 56% on each Zepbound dose and 30% on placebo^[2]. Severe ones were less common: 4.1% on Wegovy versus 0.9% on placebo^[1], and 1.7%, 2.5% and 3.1% on Zepbound 5, 10 and 15 mg versus 1% on placebo^[2]. With semaglutide, 98.1% of digestive side effects in STEP 1 to 3 were mild or moderate^[8]; with tirzepatide, the EU label reports that in its weight-management trial in people without diabetes they were mild in 60.8% of cases and moderate in 34.6%^[7].

In type 2 diabetes, at lower doses, the figures are lower: the Ozempic label reports nausea in 15.8% and 20.3% on 0.5 mg and 1 mg, versus 6.1% on placebo^[3], and the Mounjaro label nausea in 12%, 15% and 18% on 5, 10 and 15 mg, versus 4%^[4].

What to expect week by week

No label gives a week-by-week symptom calendar. Combining the dose-escalation schedules, what the labels say about when side effects cluster and the pooled trial analyses gives an approximate timeline: the average across the trials, not any one person.

Sources: Wegovy label, section 2.2 and Table 1^[1]; Zepbound label, sections 2.1 and 2.2^[2].

Ozempic and Mounjaro follow the same pattern: Ozempic starts at 0.25 mg and Mounjaro at 2.5 mg once weekly, and each increase comes after at least 4 weeks on the current dose^[3,4]. These are label schedules: the dose and the timing of each increase are your prescriber’s decision.

Weeks 1 to 4: the starting dose

The US labels set out these schedules to reduce the risk of gastrointestinal adverse reactions^[1,2]. In the EU Wegovy label, the digestive side effects, headache, dizziness, fatigue and altered taste all carry the same note: mainly seen in the dose-escalation period^[5]. The 2025 joint advisory from four US medical and nutrition societies adds that side effects are more likely in the first weeks and with dose increases, and tend to ease once the dose is stable^[10].

Two first-month details are specific to tirzepatide. The Zepbound label says tirzepatide delays gastric emptying, and the delay is largest after the first dose and diminishes over time^[2]. For that reason, the Zepbound and Mounjaro Medication Guides say birth control pills by mouth may not work as well, so your provider may recommend another type of birth control for 4 weeks after you start and for 4 weeks after each dose increase^[2,4]. If you take the pill, ask your prescriber about it before your first dose.

With each dose increase

The labels treat escalation as a whole as the period with the most symptoms: the Zepbound label says the majority of nausea, vomiting and/or diarrhea events occurred during dose escalation and decreased over time^[2]. No source breaks symptoms down step by step. In the pooled STEP 1 to 3 analysis, the vast majority of people with a digestive side effect on semaglutide had their first one during escalation, and first events leveled off after week 20. The authors read this as meaning that the extra symptoms after escalation came mostly from people who had already had one^[8].

The labels give prescribers room to slow down. The Wegovy label says that if a dose isn’t tolerated during escalation, prescribers can consider delaying the next increase for 4 weeks^[1]; the EU label also mentions lowering to the previous dose until symptoms improve^[5]. The Zepbound label says that if a maintenance dose isn’t tolerated, prescribers can consider a lower one^[2]. In STEP 1 to 3, digestive side effects led to a dose reduction or a temporary pause in 12.5% of people on semaglutide, versus 1.7% on placebo^[8]. If you’re having a hard time, tell your prescriber before the next step up.

Weeks 5 to 16: symptoms build

With Wegovy, the increases continue until week 16. In STEP 1 to 3, the share of people with nausea, diarrhea and vomiting peaked around week 20, and nausea showed the steepest decline afterward; the share with constipation leveled off earlier, around week 10^[8].

With tirzepatide, the SURMOUNT trials used a 20-week escalation period, and the first use of medicines for nausea or diarrhea was most frequent in the first 24 weeks^[9]. According to the Zepbound label, most people who stopped Zepbound because of side effects did so during the first few months, due to digestive side effects^[2].

If you miss doses

The Wegovy label links restarting after a longer gap to the risk of digestive side effects. These are the label rules, quoted for reference; what to do with your own doses is a question for your prescriber or pharmacist.

• Wegovy injection: if one dose is missed and the next is more than 2 days away, take it as soon as possible; if it’s less than 2 days away, skip it. If 2 or more consecutive doses are missed, the label tells prescribers to restart escalation at a lower dose to reduce the risk of gastrointestinal side effects, and the Medication Guide says to contact your healthcare provider about how to restart^[1].
• Zepbound and Mounjaro: take the missed dose as soon as possible within 4 days (96 hours); if more than 4 days have passed, skip it and take the next one on the usual day^[2,4].
• Ozempic: take the missed dose as soon as possible within 5 days; if more than 5 days have passed, skip it^[3].

Months 4 to 12: things settle

After that peak around week 20, the share of people with nausea, diarrhea and vomiting kept falling on semaglutide, though it stayed above placebo through week 68^[8]. In STEP 4, among people who had tolerated 20 weeks of treatment, the share with nausea, diarrhea and constipation kept falling, and almost all discontinuations for digestive side effects had happened in those first 20 weeks^[8].

Constipation lasts the longest: a median of 47 days on Wegovy versus 35 on placebo, mild or moderate^[5,8]. With Ozempic, in the SUSTAIN 9 trial and alongside an SGLT2 inhibitor (another diabetes medicine), the EU label reports constipation in 6.7%, versus none on placebo, with no decrease in its prevalence over time^[6]. I cover it in depth in constipation on GLP-1 medications.

For Zepbound, the label says no more than “decreased over time”^[2]. The 7.2 mg dose of Wegovy brings more of some side effects. In the label’s Table 4, from the two 72-week trials of that dose, nausea affected 39% on 7.2 mg, 35% on 2.4 mg and 13% on placebo, and vomiting 22%, 16% and 6%. The text of section 6.1 adds dysesthesia (altered skin sensation such as tingling, burning or sensitive skin) in 22%, 6% and 0.3%, and hair loss in 5.8%, 3.3% and 1.0%; the table rounds those to 22, 6 and 0% and to 6, 3 and 1%^[1].

The long term

For the less common side effects, the labels give no typical time of onset. Three nuances:

• Gallbladder: the Zepbound label says acute gallbladder events were associated with weight reduction^[2]. The Wegovy label says substantial or rapid weight loss can increase the risk of gallstones, but gallbladder disease was more common than on placebo even after accounting for weight loss^[1].
• Hair loss: both US labels say hair loss was associated with weight reduction^[1,2]; in the EU Wegovy label, it was more frequent in people who lost 20% of their weight or more^[5]. More below.
• Optic neuropathy (NAION): the EU Wegovy label says there is no identified time interval for when NAION may develop after starting treatment^[5].

To see your own pattern, my printable symptom diary lets you log symptoms day by day for 4 weeks and take them to your appointment.

Less common but important side effects

Sources: Wegovy label, sections 5 and 6, weight-management trials in adults^[1]; Zepbound label, sections 5 and 6, SURMOUNT-1 and -2^[2]; EU Wegovy label, section 4.8^[5]. “Versus” figures are placebo.

If pancreatitis is suspected, both US labels tell prescribers to stop the medicine and start appropriate management^[1,2]. With insulin or a sulfonylurea, the labels say the risk of low blood sugar may be lowered by reducing the dose of those medicines^[2]. That’s a call for your doctor.

NAION. Non-arteritic anterior ischemic optic neuropathy is damage to the optic nerve from poor blood flow, and it can cause vision loss. In June 2025, the EMA’s safety committee concluded that it’s a very rare side effect of semaglutide, which may affect up to 1 in 10,000 people^[12]. The EU Wegovy label adds that several large epidemiological studies in adults with type 2 diabetes link semaglutide to roughly double the relative risk, about one additional case per 10,000 person-years of treatment, and that a sudden loss of vision should lead to an eye examination, and semaglutide should be stopped if NAION is confirmed^[5]. The current US Wegovy and Ozempic labels don’t list it^[1,3].

Anesthesia and sedation. The US labels report rare cases of pulmonary aspiration (stomach contents getting into the lungs) in people on GLP-1 medicines having general anesthesia or deep sedation, who still had food in the stomach despite fasting as instructed^[1,2]. Tell all your healthcare providers that you take the medicine before any scheduled surgery or procedure, as the Medication Guides ask^[1,2].

Kidneys and eyes. The US labels describe postmarketing reports of acute kidney injury, mostly in people whose nausea, vomiting or diarrhea led to dehydration^[1,2]. In type 2 diabetes, rapid improvement in blood sugar has been associated with a temporary worsening of diabetic retinopathy^[1,2]; in the Wegovy trial in type 2 diabetes, diabetic retinopathy was reported in 4% versus 2.7% on placebo^[1].

What tends to help, and when to call your doctor

In SURMOUNT, people with digestive symptoms they couldn’t tolerate were first advised to eat smaller meals, split three daily meals into four or more, and stop eating when they felt full^[9]. The 2025 advisory suggests a small breakfast and then small meals every 3 to 4 hours, and avoiding fatty or high-fiber foods in the first few days of treatment^[10].

The advisory adds that anti-nausea medicines can help during dose increases, though some can worsen constipation^[10]: ask your prescriber or pharmacist before taking any. For day-to-day eating with a small appetite, see what to eat on GLP-1 medications and protein and muscle on GLP-1 medications. Before your next appointment, my doctor-visit checklist has side-effect questions you can print or copy.

Warning signs: what the Medication Guides say

Hair loss and “Ozempic face”

Both weight-management labels list hair loss among the common side effects. The Wegovy label’s text gives 3.3% on Wegovy (4% of women, 0.9% of men) versus 1% on placebo, the figure its Table 3, quoted above, rounds to 3%^[1]; the EU label adds that it was mostly mild and most people recovered while staying on treatment^[5]. The Zepbound label reports it more often in women (7.1%) than in men (0.5%), and no one on Zepbound stopped treatment because of it^[2]. The US Ozempic and Mounjaro labels list alopecia among reports received after approval^[3,4], and no label explains the mechanism. More in hair loss on GLP-1 medications. “Ozempic face,” on the other hand, isn’t in any label: it’s a media term, not a diagnosis, and I explain it in Ozempic face.

Frequently asked questions

How long do side effects of Ozempic, Wegovy or Zepbound last?

Most episodes last days, constipation weeks: on Wegovy, a median of 8 days for nausea and 47 for constipation^[5]. The US labels give no durations, but say nausea, vomiting and diarrhea decreased over time^[2,4]. If you’re thinking of stopping, talk to your doctor first; see stopping GLP-1 medications and weight regain.

Why does nausea come back after a dose increase?

The labels don’t say whether it returns at every step, but digestive side effects do rise with the dose. In the Mounjaro trials in type 2 diabetes, they affected 37.1%, 39.6% and 43.6% on 5, 10 and 15 mg, versus 20.4% on placebo^[4]. That’s why the dose goes up gradually, and why symptoms cluster during escalation.

Does Zepbound cause fatigue?

It can, though not often. Table 1 of the US Zepbound label groups fatigue, weakness (asthenia), lethargy and malaise under one heading: 5%, 6% and 7% on 5, 10 and 15 mg, versus 3% on placebo, and the Medication Guide lists feeling tired among the most common side effects^[2]. The EU tirzepatide label rates it very common in SURPASS-CVOT, a trial in type 2 diabetes with cardiovascular disease, and common in the weight-management trials^[7]. With semaglutide it rises with the dose: 11% on Wegovy 7.2 mg, 9% on 2.4 mg and 5% on placebo^[1]. Why isn’t established. Possible contributors: tirzepatide decreases calorie intake^[2]; vomiting or diarrhea can dehydrate you, and dehydration itself causes tiredness^[20]; and with insulin or a sulfonylurea, low blood sugar can show up as weakness, confusion or drowsiness^[2]. Tell your prescriber if it doesn’t ease; with confusion or fainting, get medical help right away^[20].

Does Ozempic cause headaches?

In the US Ozempic label, headache isn’t among the adverse reactions from its trials; it appears only among reports received after approval, whose frequency and link to the drug can’t be reliably established^[3]. The EU Ozempic label rates headache common (up to 1 in 10 people)^[6]. At Wegovy’s higher semaglutide doses, the excess over placebo is small (table above); in the 7.2 mg trials it was 9% on 7.2 mg, 8% on 2.4 mg and 7% on placebo^[1]. Research points the other way too: in a small uncontrolled pilot study, liraglutide, another GLP-1 medicine, nearly halved headache days in 31 people with obesity and frequent or chronic migraine^[17]. One known cause: the Medication Guide lists headache among the signs of low blood sugar, a risk mainly with insulin or a sulfonylurea^[3]. Get help right away for a sudden, explosive or “worst ever” headache, or one with vision changes or confusion^[21].

Does Zepbound cause insomnia?

The US Zepbound label doesn’t list insomnia, either from its trials or among reports after approval^[2], and neither do the other US and EU semaglutide and tirzepatide labels I checked^{[1,3,4,5,6,7]}. In the sleep apnea trials, the label reports adverse reactions similar to those in the weight-management trials, and improvement in sleep-related impairment compared with placebo^[2]; more in Zepbound for sleep apnea. The only signal comes from the FDA’s voluntary reporting database: across GLP-1 medicines, a narrow insomnia category (75 reports) was reported about twice as often as with other drugs, an association that doesn’t show cause^[16]. Nausea or reflux at night could plausibly disturb sleep, but that hasn’t been studied; see acid reflux on GLP-1 medications. If poor sleep persists, tell your prescriber. Why sleep matters for hunger is in sleep, stress and appetite.

What are sulfur burps on Ozempic?

It’s a popular name, not a medical term, for burps that smell of rotten eggs. The labels list burping (eructation) but say nothing about its smell. In the US Ozempic label, burping affected 2.7% on 0.5 mg and 1.1% on 1 mg, versus 0% on placebo; indigestion 3.5% and 2.7%, versus 1.9%; and reflux (GERD) 1.9% and 1.5%, versus 0%^[3]. Wegovy and Zepbound figures are in the table above. A plausible but unstudied explanation: Ozempic delays gastric emptying^[3], so food stays longer in the stomach, and the NIDDK notes that the odor of passed gas may be due to sulfur^[18]. To swallow less air, the NIDDK suggests eating more slowly and avoiding fizzy drinks, straws and chewing gum^[19]. Tell your prescriber if you have stomach problems that are severe or will not go away^[3].

Do Ozempic and Wegovy have the same side effects?

The profile is similar; the Ozempic label reports lower figures, at lower doses and in type 2 diabetes^[3]. Hair loss is a common side effect in the Wegovy label but appears in the US Ozempic label only among reports after approval^[1,3]. More in Ozempic vs. Wegovy.

Which causes more side effects, Ozempic or Mounjaro?

The labels don’t let you compare them, because their figures come from different trials^[1,2]. In SURMOUNT-5, which compared tirzepatide and semaglutide head to head in obesity without a placebo group, the most common side effects with both were digestive^[11]. Which treatment fits you is a decision to make with your doctor. There’s more in Ozempic vs. Mounjaro and in my semaglutide and tirzepatide guides.

Does Mounjaro or Zepbound have sexual side effects?

Neither US label lists sexual side effects among its adverse reactions^[2,4]. One related point: tirzepatide may make birth control pills by mouth work less well for a few weeks after starting and after each dose increase^[2,4]. If you notice any change, mention it to your doctor.

Are these medicines linked to suicidal thoughts?

In April 2024, the EMA’s safety committee concluded that the available evidence doesn’t support a causal link between GLP-1 receptor agonists, semaglutide included, and suicidal thoughts or actions^[13]; that review didn’t include tirzepatide. In January 2026, after its own review, the FDA found no increased risk and asked the makers of Saxenda, Wegovy and Zepbound to remove the warning from their labels^[14]. If you’re thinking of harming yourself, get help now: in the US, call or text 988, the Suicide & Crisis Lifeline^[14].

Do more side effects mean the medication works better?

The trial analyses don’t support that. In STEP 1 to 3, digestive side effects explained less than 1 percentage point of the weight lost with semaglutide beyond placebo^[8]. In SURMOUNT-1 to -3, they were associated with at most 3.1% of the total weight lost with tirzepatide^[9].

Why am I so tired the day after my shot, and does it ease?

The labels don’t time fatigue to the injection, so that pattern hasn’t been measured. What they do say: tirzepatide reaches its peak blood level a median of 24 hours after the injection (range 8 to 72 hours), and Wegovy’s semaglutide 1 to 3 days after the dose^[1,2]. A day-after dip fits that timing, but it’s a guess, not a finding. On whether it eases, the EU Wegovy label marks fatigue as seen mainly during the dose-escalation period^[5]. How common fatigue is, and what can add to it, is in Does Zepbound cause fatigue?. The Zepbound label allows changing the injection day as long as the doses are at least 3 days (72 hours) apart^[2]; whether that makes sense for you is a question for your prescriber. Noting it in the symptom diary helps.

Why does food sit worse two or three days after my shot?

The labels don’t tie digestive symptoms to a day of the week, and I haven’t found a study that measures it, so what follows is a hypothesis. It lines up with when the drug peaks in your blood, which I cover in the answer on tiredness. Both drugs also slow stomach emptying, an effect the labels describe as fading. The Zepbound label says the delay is largest after the first dose and this effect diminishes over time^[2], and the Ozempic label reports that no apparent effect on the rate of gastric emptying was observed with semaglutide 2.4 mg in a separate study^[3]. The labels give no food advice; what the trials suggested is in what tends to help, with more in nausea on GLP-1 medications and foods to avoid on Ozempic. Don’t change your dose or injection day on your own: bring it up with your prescriber.

Can Zepbound or Wegovy cause vivid dreams or nightmares?

Not according to the labels: vivid dreams and nightmares don’t appear in the US labels for Zepbound, Mounjaro, Wegovy or Ozempic, or in the EU labels I checked^{[1,2,3,4,5,6,7]}. I also found no case reports on PubMed linking these medicines to dreams. The FDA reporting-database study in the insomnia answer flagged eight psychiatric reactions reported more often than expected, such as nervousness, stress and binge eating; abnormal dreams and nightmares weren’t among them^[16]. That doesn’t rule out an effect, since unexpected effects are often underreported. If your dreams are disturbing your sleep or come with low mood, note when they happen in the symptom diary and tell your prescriber.