Mounjaro / Tirzepatide — Side Effects and Safety Profile (Vascular Surgeon’s Guide)

In the first two articles of this series I covered how the dual-action weight-loss shot works and the positive effects observed in patients. Now to the part that, as a clinician, I monitor most carefully: side effects and safety. This article is a plain-language guide to the common gastrointestinal effects, the rare-but-important events (pancreatitis, gallbladder disease, retinopathy progression), the absolute and relative contraindications, drug interactions and surgical considerations, and the warning signs that require immediate medical attention.

Disclaimer: This article is informational about a prescription drug; it is not medical advice. The decision to start this injection is always made together with the physician who examines you.

Most common side effects (gastrointestinal)

The vast majority of side effects affect the digestive system and stem directly from the drug’s mechanism. Slowed gastric emptying and central appetite-modulating action explain most of these.

Across the SURMOUNT and SURPASS programmes, the highest-dose (15 mg) frequencies were:

• Nausea ≈ 25–30% (mostly during the first weeks, after dose escalation)
• Diarrhoea ≈ 19–20%
• Vomiting ≈ 10–13%
• Constipation ≈ 9–11%
• Abdominal pain, dyspepsia, eructation, flatulence at lower rates

The vast majority of these effects are mild to moderate and tend to subside as the dose is gradually increased. Even so, around 4–7% of patients discontinued the drug because of side effects (Jastreboff et al., NEJM 2022).

Practical tips

• Smaller, more frequent meals; less heavy or fatty food
• Avoid large fast meals soon after the injection — eat slowly
• Plenty of water during the first doses (prevent dehydration)
• If side effects persist or are severe, delaying dose escalation can be discussed with your physician

Rarer but important side effects

These categories are uncommon but illustrate why physician follow-up matters.

Acute pancreatitis

This is a class-related concern for GLP-1 receptor agonists. Across the four-year follow-up of SURPASS-CVOT, the incidence of pancreatitis with tirzepatide was similar to that with dulaglutide. Still, in case of persistent and severe abdominal pain (radiating to the back, worsening with meals), the drug should be stopped immediately and emergency evaluation performed (Nicholls et al., NEJM 2025).

Gallbladder events (stones, inflammation, cholecystitis)

Rapid weight loss in any setting increases the risk of gallstones. Across the GLP-1 receptor agonist class the risk increases roughly 1.4-fold (He et al., JAMA Internal Medicine 2022;182(5):513–519). Right upper-quadrant pain, post-fatty-meal pain, or fever warrants medical assessment.

Hypoglycaemia (low blood sugar)

Hypoglycaemia risk with tirzepatide as monotherapy is low because it stimulates insulin secretion in a glucose-dependent manner. However, when combined with insulin or sulfonylureas (gliclazide, glimepiride, etc.), serious hypoglycaemia can occur. In that case the physician usually reduces the partner drug.

Diabetic retinopathy progression

Rapid HbA1c lowering can transiently worsen pre-existing diabetic retinopathy. In patients with type 2 diabetes, retinal examination before and during treatment is recommended.

Indirect renal effects

Severe nausea and vomiting can cause dehydration with transient renal impairment. Adequate fluid intake and close monitoring in patients with underlying kidney disease are essential.

Injection-site reactions and hypersensitivity

Mild redness, itching or swelling at the abdominal injection site can occur, usually resolving within a few days. Anaphylaxis has rarely been reported; shortness of breath, lip/tongue swelling or generalised rash require emergency evaluation.

Absolute and relative contraindications

Tirzepatide should not be used, or should only be considered after specialist evaluation, in any of the following:

• Medullary thyroid carcinoma (MTC) — personal or first-degree family history
• Multiple endocrine neoplasia type 2 (MEN-2) syndrome
• History of severe pancreatitis
• Hypersensitivity to any component (history of anaphylaxis)
• Active or uncontrolled advanced gastroparesis / severe gastrointestinal disorders
• Pregnancy and breastfeeding — insufficient safety data; if pregnancy is planned, the drug should be discontinued at least 1 month in advance
• Under 18 years of age — off-label, paediatric data limited

This list is compiled from StatPearls / NCBI Bookshelf and FDA prescribing information. (Because thyroid C-cell tumours were observed in rats, MTC/MEN-2 remain absolute contraindications; a causal relationship in humans has not been demonstrated, but the precaution is maintained.)

Drug interactions and surgical planning

Because tirzepatide slows gastric emptying, two important interactions arise:

• Delayed oral-drug absorption: the effectiveness of some oral medications (including oral contraceptives) may fluctuate — alternative contraception or barrier methods should be discussed with your physician.
• Pre-operative planning: to reduce the risk of pulmonary aspiration during anaesthesia, the American Society of Anesthesiologists (ASA) 2023/2024 consensus recommends discontinuing tirzepatide generally one week before elective surgery (for weekly injections). In emergency surgery, the anaesthesia team must be informed.

When should you contact your doctor immediately?

If any of the following develops, do not continue using the drug and contact your physician without delay:

• Severe, persistent abdominal pain radiating to the back (especially worsening after meals) → suspect acute pancreatitis
• Right upper-quadrant pain + fever + jaundice → cholecystitis / biliary obstruction
• Persistent vomiting + reduced urine output + weakness → severe dehydration, risk of kidney injury
• An enlarging neck mass, hoarseness, or difficulty swallowing → thyroid evaluation required
• Shortness of breath, lip/tongue swelling, generalised rash → hypersensitivity reaction
• Severe dizziness, sweating, palpitations (in patients on insulin/sulfonylureas) → serious hypoglycaemia

From the vascular surgeon’s perspective + Summary

In vascular practice — varicose veins and venous disease, lymphedema and lipedema, peripheral arterial disease — most of our patients carry obesity, hypertension and a high metabolic burden. Tirzepatide can be a powerful tool against these burdens; however, careful side-effect management and surgical planning (e.g. before chronic venous insufficiency or varicose-vein interventions) make multidisciplinary coordination essential.

In summary:

• Most common side effects are transient gastrointestinal complaints that ease with dose titration.
• Pancreatitis, gallbladder events, and retinopathy progression are rare but should not be overlooked.
• MTC, MEN-2, history of severe pancreatitis, and pregnancy are absolute contraindications.
• For elective surgery, discontinue 1 week beforehand.
• Hydration and physician follow-up during the first weeks are critical.

For the right patient, tirzepatide can deliver substantial benefit; but the benefit–risk balance must be set individually for each patient. The aim of this three-part series is to give my patients the foundational knowledge they need to make informed treatment decisions.

For an evaluation tailored to your health needs, please feel free to reach out via the contact page or read more on the about page.

Scientific References

1. Jastreboff AM, Aronne LJ, Ahmad NN et al. Tirzepatide Once Weekly for the Treatment of Obesity (SURMOUNT-1). N Engl J Med. 2022;387:205–216. DOI:10.1056/NEJMoa2206038 — nejm.org/doi/full/10.1056/NEJMoa2206038
2. Nicholls SJ, Pavo I, Bhatt DL et al. Cardiovascular Outcomes with Tirzepatide versus Dulaglutide in Type 2 Diabetes (SURPASS-CVOT). N Engl J Med. 2025;393:2409–2420. DOI:10.1056/NEJMoa2505928 — nejm.org/doi/full/10.1056/NEJMoa2505928
3. He L, Wang J, Ping F et al. Association of GLP-1 Receptor Agonists With Risk of Acute Gallbladder or Biliary Diseases. JAMA Intern Med. 2022;182(5):513–519. DOI:10.1001/jamainternmed.2022.0338 — jamanetwork.com/journals/jamainternalmedicine/fullarticle/2790534
4. Frias JP, Davies MJ, Rosenstock J et al. Tirzepatide versus Semaglutide Once Weekly in Patients with Type 2 Diabetes (SURPASS-2). N Engl J Med. 2021;385:503–515. DOI:10.1056/NEJMoa2107519 — nejm.org/doi/full/10.1056/NEJMoa2107519
5. American Society of Anesthesiologists. Consensus-Based Guidance on Preoperative Management of Patients on GLP-1 Receptor Agonists. 2023 (updated 2024). asahq.org
6. Tirzepatide. StatPearls. NCBI Bookshelf, 2024. ncbi.nlm.nih.gov/books/NBK585056