How tirzepatide works
Tirzepatide activates receptors for two gut hormones: GLP-1 and GIP. GLP-1 regulates appetite and how much you eat, and the label says early studies suggest GIP adds to that effect. Both receptors sit in brain areas that control appetite. Tirzepatide also helps the pancreas release insulin when blood sugar is high and slows stomach emptying.
- Zepbound is approved for weight reduction and long-term maintenance in adults with obesity, or overweight with a weight-related condition, and for moderate to severe obstructive sleep apnea in adults with obesity.
- Mounjaro is approved for blood sugar control in adults with type 2 diabetes.
It's a once-weekly injection. Wondering how it relates to other GLP-1s? See is tirzepatide a GLP-1.
Common side effects
| Side effect | Zepbound (range across doses) | Placebo |
|---|---|---|
| Nausea | 25% to 29% | 8% |
| Diarrhea | 19% to 23% | 8% |
| Constipation | 11% to 17% | 5% |
| Vomiting | 8% to 13% | 2% |
| Abdominal pain | 9% to 10% | 5% |
| Indigestion | 9% to 10% | 4% |
| Injection site reactions | 6% to 8% | 2% |
| Tiredness | 5% to 7% | 3% |
| Hair loss | 4% to 5% | 1% |
Other listed side effects include allergic-type reactions such as rash and itching, burping, reflux, gas, bloating, dizziness and low blood pressure. Hair loss was tied to weight loss and was reported more in women (7.1%) than men (0.5%).
About 5% to 7% of people on Zepbound stopped because of side effects, compared with 3.4% on placebo, mostly in the first few months and mostly for stomach effects.
Serious side effects and warnings
- Thyroid tumors (boxed warning). Tirzepatide caused thyroid C-cell tumors in rats; it isn't known whether it does in people. It isn't used with a personal or family history of medullary thyroid cancer or MEN 2.
- Pancreatitis. Stop and get care if it's suspected.
- Gallbladder disease. In trials, gallbladder inflammation occurred in 0.7% on Zepbound and 0.2% on placebo.
- Kidney injury from fluid loss after vomiting or diarrhea.
- Severe stomach and intestinal reactions; not recommended with severe gastroparesis.
- Low blood sugar when used with insulin or a sulfonylurea.
- Diabetic eye disease can worsen in people with type 2 diabetes and a history of retinopathy.
- Serious allergic reactions, including swelling of the face or throat.
- Aspiration during anesthesia. Tell every clinician you take it before surgery or sedation.
Tirzepatide can make birth control pills less reliable because it slows stomach emptying. The label advises switching to a non-oral method or adding a barrier method for 4 weeks after starting and after each dose increase. More on pregnancy in tirzepatide and alcohol.
Stop and get medical care right away for stomach pain that won't go away, with or without vomiting, especially if it spreads to your back; swelling of your face, mouth, tongue or throat, hives, or trouble breathing or swallowing; dizziness with a racing heartbeat; or a lump in your neck, hoarseness or shortness of breath.
Is tirzepatide safe?
The FDA approved Zepbound for weight management in November 2023; tirzepatide was already approved as Mounjaro for type 2 diabetes. In the trials behind the label, most side effects were stomach-related. Serious problems are uncommon, but they happen, and some people shouldn't use it at all.
Safety also depends on the product. The FDA warns that tirzepatide sold online "for research purposes" or "not for human consumption" is unapproved and of unknown quality, and it has received reports of dosing errors, some needing hospital care, when people measured doses themselves. Compounded medications aren't FDA-approved. A licensed clinician decides what's right for you.
Through Gabriel, a licensed clinician reviews every prescription request and decides whether tirzepatide fits your history. Your clinician decides the dose.
Common questions
What are the most common side effects of tirzepatide?
Nausea, diarrhea, constipation, vomiting, stomach pain and indigestion. They happen most while the dose is being raised.
Does tirzepatide have more side effects than semaglutide?
The side effects are similar and mostly stomach-related. See tirzepatide vs semaglutide for head-to-head trial data.
Does tirzepatide cause hair loss?
Hair loss was reported in 4% to 5% of people on Zepbound versus 1% on placebo in trials. It was linked to weight loss and was more common in women.
Can tirzepatide affect birth control?
Yes. It can make birth control pills less effective. The label advises a non-oral method or a backup barrier method for 4 weeks after starting and after each dose increase.
Who shouldn't take tirzepatide?
People with a personal or family history of medullary thyroid cancer or MEN 2, or a serious allergy to tirzepatide. It isn't recommended with severe gastroparesis or during pregnancy, and it shouldn't be combined with other GLP-1 drugs.
Sources
- Zepbound (tirzepatide) prescribing information, revised 08/2026 Eli Lilly
- Tirzepatide Injection MedlinePlus
- FDA approves new medication for chronic weight management U.S. Food and Drug Administration
- FDA's concerns with unapproved GLP-1 drugs used for weight loss U.S. Food and Drug Administration
This guide is general information, not medical advice. It does not replace a visit with a licensed clinician. Gabriel membership is not health insurance.