Mounjaro Injection Site Reactions: When to Call Your Doctor

What does the Mounjaro label say to watch for?

The Mounjaro label's serious-reaction warning is about hypersensitivity. It says anaphylaxis and angioedema have been reported with Mounjaro. If a hypersensitivity reaction is suspected, the label says to discontinue Mounjaro, treat promptly per standard of care, and monitor until signs and symptoms resolve [1]. It also says not to use Mounjaro in patients with a previous serious hypersensitivity reaction to tirzepatide or any excipient [1]. For patients with a history of angioedema or anaphylaxis with a GLP-1 receptor agonist, the label says to use caution because it is unknown whether they are predisposed to these reactions with Mounjaro [1].

Anaphylaxis is a severe, whole-body allergic reaction, and angioedema is deep swelling of the skin or mucous membranes, often of the face, lips or throat. The label names these two as the serious hypersensitivity reactions reported with Mounjaro [1].

How often do injection-site reactions happen with Mounjaro?

In the Mounjaro label's pool of placebo-controlled adult trials, injection site reactions were reported in 3.2% of Mounjaro-treated patients versus 0.4% of placebo-treated patients; hypersensitivity reactions were reported in 3.2% versus 1.7% [1]. The label's Table 1 of reactions reported in at least 5% of patients lists nausea, diarrhea, decreased appetite, vomiting, constipation, dyspepsia and abdominal pain [1].

A separate pooled immunogenicity analysis looked at 5,025 tirzepatide-treated adults with type 2 diabetes across seven phase 3 trials [2]. Treatment-emergent anti-drug antibodies developed in 51.1% of patients. More patients with anti-drug antibodies had hypersensitivity reactions or injection-site reactions than patients without them; the label gives 4.6% (119 of 2,570) of antibody-positive versus 0.7% (18 of 2,455) of antibody-negative adults for injection site reactions [1][2]. The majority of those hypersensitivity and injection-site events were nonserious and nonsevere [2].

Local reaction versus serious allergic reaction

The label lists injection site reactions and hypersensitivity reactions as separate adverse reactions [1]. Its stop-and-seek-advice instruction is tied to suspected serious hypersensitivity, meaning anaphylaxis or angioedema [1]. For injection technique, the label says to inject in the abdomen, thigh, or back of the upper arm by another person, and to rotate injection sites with each dose [1].

What the label says about the injection

The label says to inject Mounjaro subcutaneously in the abdomen or thigh, or have another person inject in the back of the upper arm, and to rotate injection sites with each dose [1]. It says the solution should appear clear and colorless to slightly yellow, and not to use it if particulate matter or discoloration is seen [1]. It also says never to share a Mounjaro KwikPen between patients, even if the pen needle is changed [1].