Zepbound vs Wegovy Side Effects: Head-to-Head Comparison from the FDA Labels (2026)

Zepbound and Wegovy share the same boxed warning, the same GI-dominant adverse-reaction profile, and the same warnings/precautions list. The differences are quantitative rather than categorical — tirzepatide (Zepbound) reports a slightly higher incidence of GI events at top doses than semaglutide (Wegovy) in the SURMOUNT-1 and SURMOUNT-5 trials. Below: the verbatim §6 ADVERSE REACTIONS comparison from both DailyMed FDA labels, plus the SURMOUNT-5 head-to-head safety data.

Boxed warning — identical in both labels

Both Zepbound and Wegovy carry the same FDA boxed warning about thyroid C-cell tumors based on rodent carcinogenicity studies with GLP-1 receptor agonists. The wording is substantively identical:

“In rodents, [tirzepatide / semaglutide] causes thyroid C-cell tumors. It is unknown whether [tirzepatide / semaglutide] causes thyroid C-cell tumors, including medullary thyroid carcinoma (MTC), in humans. [Zepbound / Wegovy] is contraindicated in patients with a personal or family history of MTC and in patients with Multiple Endocrine Neoplasia syndrome type 2 (MEN 2). Counsel patients regarding the potential risk for MTC and symptoms of thyroid tumors.”

Clinical relevance to humans is debated — large post-marketing surveillance has not produced a clear causal signal for MTC in human GLP-1 users. The boxed warning is a conservative regulatory response to the rodent data, not a direct human observation.

Most common adverse reactions side-by-side

From the §6 ADVERSE REACTIONS sections — events reported by ≥5% of patients in pooled trials and more frequently than in the placebo arm:

Counter-intuitive finding: the headline Wegovy GI rates (44% nausea, 30% diarrhea, 24% vomiting) are higher than the headline Zepbound rates (29% nausea, 21% diarrhea, 13% vomiting) — but this comparison is across DIFFERENT trial populations and different titration schedules. SURMOUNT-5 (NEJM 2025) is the only direct head-to-head, and it reported similar overall tolerability with slightly more GI events on tirzepatide at the highest dose tier. Cross-trial comparison is misleading because the patient populations, diet/lifestyle controls, and titration speed differ.

Warnings and precautions — also identical

Both labels list the same §5 WARNINGS AND PRECAUTIONS:

• Risk of thyroid C-cell tumors (the boxed warning content)
• Acute pancreatitis — discontinue if suspected and do not restart if confirmed
• Acute gallbladder disease — including cholelithiasis and cholecystitis. Patients should be monitored for symptoms.
• Hypoglycemia — particularly when used in combination with insulin secretagogues or insulin in patients with type 2 diabetes
• Acute kidney injury — secondary to severe GI volume loss in patients with persistent vomiting or diarrhea
• Hypersensitivity reactions — including anaphylaxis and angioedema
• Diabetic retinopathy complications in patients with type 2 diabetes
• Suicidal behavior and ideation — monitor for new or worsening depression, suicidal thoughts, or unusual changes in mood/behavior
• Risk of ileus — Wegovy label updated 2024 to add ileus warning; Zepbound label includes the same warning
• Pulmonary aspiration during anesthesia — per ASA 2024 multisociety guidance (added to the labels)
• Severe gastrointestinal disease — neither drug is recommended in patients with severe gastroparesis

For our deep dive on each warning category, see: gallbladder + gallstones evidence, ileus + bowel obstruction evidence, medullary thyroid cancer evidence, peri-operative ASA guidance (Spanish), and bone density and fracture risk evidence.

Contraindications — identical

Both labels list the same §4 CONTRAINDICATIONS:

• Personal or family history of medullary thyroid carcinoma (MTC)
• Multiple Endocrine Neoplasia syndrome type 2 (MEN 2)
• Known serious hypersensitivity to the drug (tirzepatide / semaglutide) or any of its excipients

SURMOUNT-5 head-to-head safety (NEJM 2025)

SURMOUNT-5 (Aronne et al., NEJM 2025, PMID 39891752) is the only published head-to-head trial comparing tirzepatide and semaglutide for chronic weight management. It enrolled 750+ adults with obesity (without type 2 diabetes) and randomized them to maximum-tolerated doses of tirzepatide (Zepbound) or semaglutide 2.4 mg (Wegovy) over 72 weeks.

Safety findings (verbatim from the publication abstract):

• The most frequently reported adverse events with both drugs were gastrointestinal in nature, primarily mild to moderate in severity
• Discontinuation rates due to adverse events were similar between the two arms
• Tirzepatide produced greater mean weight loss (~22% vs ~14% at 72 weeks) — confirming the indirect comparison from SURMOUNT-1 and STEP-1

The clinical implication: if the head-to-head trial shows similar tolerability between the two drugs, the side-effect profile is unlikely to be the deciding factor for an individual patient. Cost, insurance coverage, dose schedule preference, and personal contraindications usually dominate.

Practical takeaways

• Both drugs share the same boxed warning + same contraindications. If you have a personal or family history of medullary thyroid carcinoma or MEN 2, neither drug is appropriate.
• Both drugs have the same warnings/precautions list. Acute pancreatitis, gallbladder disease, hypersensitivity, kidney injury risk in setting of severe GI loss, ileus risk, peri-operative aspiration risk — monitor identically on both.
• Cross-trial side-effect rates are NOT directly comparable. Wegovy's STEP-1 enrolled different patients with different baseline characteristics than Zepbound's SURMOUNT-1. The headline % differences (Wegovy 44% nausea vs Zepbound 29%) reflect trial design differences, not necessarily molecule differences.
• SURMOUNT-5 (NEJM 2025) is the canonical head-to-head safety reference. It found similar tolerability between tirzepatide and semaglutide in directly comparable conditions.
• Most GI side effects peak during dose escalation and decrease at maintenance dose. If you titrate slowly and your prescriber drops you back to the previous dose when GI tolerance fails, both drugs are tolerable for the majority of patients.