Mounjaro in the abdomen, thigh or upper arm? Why it is injected under the skin

Where should the medicine go?

The medicine should go into the tissue beneath the skin. The manufacturer clearly states that Mounjaro must not be injected into a muscle or a vein. [194]

Having fat around the abdomen may raise a question: can the medicine be absorbed from there? However, this medicine is specifically intended to be injected under the skin. Having more fatty tissue is not a reason to try to inject deeper. The official product information allows abdominal injections, including in people being treated for obesity, and does not recommend changing the route of administration according to body weight. [195]

What do studies say about injection sites?

Researchers have investigated whether the injection site matters. In an analysis published in 2024 using data from 19 studies, they described how tirzepatide is absorbed and how long it stays in the body. They found similar drug exposure after injections under the skin of the abdomen, thigh and upper arm. [196]

In simpler terms, the amount of medicine the body was exposed to over time was similar across these three injection sites. This does not mean that every patient will feel exactly the same effects, but it does not support calling any one site consistently more effective. [196]

Why must Mounjaro not be injected into a muscle?

1. It is not known how this change would affect absorption. The studies cited do not compare injections under the skin with injections into a muscle. They therefore cannot support claims that an injection into a muscle would act faster, have a stronger effect or wear off sooner. [196]

2. Treatment recommendations apply to injections under the skin. Established dosing and safety findings should not be assumed to apply to a different route of administration. The manufacturer explicitly states that Mounjaro must not be injected into a muscle. [194]

3. An incorrectly performed injection can cause injury. Pain, bruising and damage to blood vessels or nerves are among the possible problems associated with incorrectly performed intramuscular injections. These are general risks of the procedure — not findings from a study showing a particular rate of such complications with intramuscular Mounjaro. [197]

4. No weight-loss benefit has been demonstrated. The studies discussed do not provide evidence that injecting into a muscle increases weight loss or suppresses appetite more strongly. They do not support treating this type of injection as a way to improve the medicine’s effect. [196]

What should you remember when choosing a site?

In practice, the options are the abdomen, at least 5 cm away from the belly button, the thigh or the back of the upper arm. Another person should give an injection into the back of the upper arm. Change the exact injection spot with each dose; you can continue to use the same area of the body. Check the instructions supplied with your particular pack for details on using the pen. [195]

You can read more about how this substance works and what it is used for in the separate tirzepatide profile.

Where does this information come from?