Side effects, week by week

How to read this page

No label or trial lays out side effects one week at a time. What exists is the label schedule for raising the dose, plus trial findings that digestive side effects were reported mostly during that raising period. This page puts the two side by side. It is not a forecast of how any one person will feel.

The dose steps below are what the labels describe. Your prescriber sets your plan, and can slow it down.

The label dose steps

Both medicines start low and go up in steps. These come from the U.S. labels on DailyMed, which were the current versions when the Atlas checked.

• Wegovy injection: 0.25 mg a week for weeks 1 to 4, 0.5 mg for weeks 5 to 8, 1 mg for weeks 9 to 12, and 1.7 mg for weeks 13 to 16. From week 17 the label names a maintenance dose, 2.4 mg or 1.7 mg for weight reduction, and describes a higher dose of up to 7.2 mg after 2.4 mg has been tolerated for at least 4 weeks. If a dose is not tolerated, the label says to consider delaying the next step for 4 weeks.
• Zepbound: 2.5 mg a week for 4 weeks, which the label says is for starting only and not for maintenance. Then 5 mg, and after that 2.5 mg steps, each after at least 4 weeks on the current dose. Maintenance doses for weight reduction are 5, 10 or 15 mg, with 15 mg the maximum.

Weeks 1 to 4: the starting dose

The starting doses are not meant to be the working dose. They give the body time to adjust. The Atlas did not find a label or trial that reports symptoms for the starting dose on its own, so it cannot say how many people feel sick during these first weeks.

What the tirzepatide trials do show is that people who needed medicines for nausea or diarrhea mostly started using them in the first 24 weeks, which covers the whole 20-week dose-raising period in those trials.

Each time the dose goes up

Both labels say digestive reactions were mostly reported during dose escalation. The Zepbound label adds that nausea, vomiting and diarrhea decreased over time. A 2025 analysis of the four SURMOUNT trials reached the same conclusion: most digestive events were mild to moderate and clustered around the dose-raising period.

Because the dose goes up every four weeks or so, many people notice symptoms return, or get stronger, after a step and then settle. That pattern fits the trials, but the trials did not measure how many days an episode lasts, so the Atlas cannot give a typical number of days.

Week 17 and beyond: maintenance

Once the dose stops changing, the trials suggest fewer new digestive problems. The Zepbound label says most stopping because of side effects happened in the first few months. The Atlas did not find a label or trial that reports symptom rates at each month after the dose settles.

How common: the label numbers

These are the percentages of trial participants reporting each problem, from the official labels. Different trials with different people cannot be compared head to head, so treat the two medicines as separate sets of numbers.

• Wegovy 2.4 mg versus placebo: nausea 44% versus 16%, diarrhea 30% versus 16%, vomiting 24% versus 6%, constipation 24% versus 11%. Severe digestive reactions were 4.1% versus 0.9%. Stopping because of digestive reactions was 4.3% versus 0.7%.
• Zepbound versus placebo, by dose: nausea 25% (5 mg), 29% (10 mg), 28% (15 mg) versus 8%. Diarrhea 19%, 21%, 23% versus 8%. Vomiting 8%, 11%, 13% versus 2%. Constipation 17%, 14%, 11% versus 5%. Stopping because of digestive reactions was 1.9%, 3.3% and 4.3% versus 0.5%.
• In STEP 8, a head-to-head trial, 84.1% of people on semaglutide 2.4 mg and 82.7% on daily liraglutide 3.0 mg reported at least one digestive event over 68 weeks.
• Across the four SURMOUNT trials, 27.8% to 72.8% of people on tirzepatide reported a digestive event versus 12.2% to 32.5% on placebo, and 1.0% to 10.5% stopped because of them. The range is wide because the trials had different designs and people.

Does feeling sick mean it is working?

Not necessarily. In the SURMOUNT analysis, people who had nausea, vomiting or diarrhea lost a similar amount of weight to those who did not. For example, in SURMOUNT-1 at 72 weeks people with no nausea lost 19.7% of their weight, those with nausea alone 22.0%, and those with any nausea, vomiting or diarrhea 22.5%. The authors estimated the side effects explained up to about 3% of the total weight loss. This was a post hoc analysis funded by the manufacturer, so it points to a pattern and does not prove cause.

What the trials did to manage symptoms

In the SURMOUNT trials, people with intolerable digestive symptoms were first counseled on food changes. These were eating smaller meals, splitting the day into four or more smaller meals, and stopping when full. If that was not enough, investigators could prescribe medicine for nausea or diarrhea. One weekly dose could be skipped, and the dose could be lowered to the next step down. If nothing worked, the person stopped the medicine.

The authors of that analysis also list avoiding fatty foods and eating bland foods as strategies used in practice. Food-based tips for constipation, and the protein targets some experts propose, are on the constipation page and the protein page.

What people report in communities

People on these medicines commonly share things they try, such as smaller portions, slowing down, bland foods, ginger and more fluids. Some say symptoms are worst in the days right after the injection. These are personal reports, not tested treatments, and the Atlas did not find trials comparing them. Ask your clinician before adding any medicine or supplement.

When to call your prescriber

The labels name several problems that need attention. In plain terms:

• Pancreatitis: both labels say to watch for persistent, severe belly pain that may spread to the back, and to stop the medicine if pancreatitis is suspected.
• Gallbladder problems: gallstones and gallbladder inflammation happened more often than with placebo. The labels call for follow-up if gallstones are suspected.
• Dehydration and kidney injury: vomiting and diarrhea can cause fluid loss, and both labels report kidney injury cases, some needing dialysis, mostly in people with digestive losses. If you cannot keep fluids down, call early.
• Eye problems: if you have diabetic retinopathy, the labels advise monitoring, because quick improvement in blood sugar was linked to temporary worsening.
• Planned surgery or sedation: both labels say to tell your providers before any procedure, because rare cases of food or liquid entering the lungs were reported during anesthesia.

Questions to ask

• What is my dose plan, and who can slow it down if I feel unwell?
• Which symptoms should make me call you the same day?
• Is it safe for me to take anything for nausea or constipation?
• What should I do if I miss a dose or need to skip one?
• Should I tell my other doctors or my dentist before a procedure?

What is still unknown

• The Atlas found no label or trial that reports symptoms week by week or says how long a typical episode lasts.
• Trials report group percentages, so they cannot predict who will have side effects.
• No randomized trial the Atlas found tested the food, ginger or timing tips people share online.
• Real-world dose schedules often differ from the label schedules.