Tirzepatide safety study finds medication errors top FDA report signal list

An analysis of 123,145 reports to the FDA's adverse event database found that medication errors and injection-site reactions were the strongest safety signals associated with tirzepatide, the active ingredient in Mounjaro and Zepbound, ranking ahead of gastrointestinal problems ^[1].

The study drew on reports filed between the second quarter of 2022 and the fourth quarter of 2025, a window that begins around the drug's first FDA approval for type 2 diabetes in 2022 and extends past its 2023 approval for chronic weight management ^[1]. Those reports contained 251,435 individual adverse events ^[1]. Only reports listing tirzepatide as the primary suspected drug were included, and the researchers used four statistical methods — ROR, PRR, IC and EBGM — to flag events reported more often than expected ^[1].

Women accounted for 62.30% of the reports, and the mean age of the people described was 53.7 years ^[1]. Adverse events were coded using MedDRA, a standard medical dictionary used in drug safety work ^[1].

Medication errors ahead of stomach side effects

The abstract lists medication errors, injection-site reactions and gastrointestinal disorders as the major signals, and states that medication errors and injection-site reactions were the strongest of the three ^[1]. Gastrointestinal complaints such as nausea have been the most widely publicized side effects of this drug class, so a ranking that places medication errors above them is notable.

The study also compared reporting patterns for tirzepatide against semaglutide, the drug in Ozempic, Wegovy and Rybelsus. Reports involving tirzepatide showed lower reporting odds of vomiting, constipation and decreased appetite ^[1]. That comparison is based on report counts, not on a head-to-head clinical trial, and the abstract does not give the number of semaglutide reports used or the absolute rates behind the comparison.

Four signals described as "novel" and "unlabelled" appeared in the data: eructation, hunger, food craving and starvation ketoacidosis ^[1]. "Unlabelled" means the event is not listed in the FDA-approved product labeling, and the study's authors wrote that these signals "warrant further investigation" rather than establishing a cause ^[1].

Most reports came early

Among reports that contained usable onset information, the median time from starting the drug to the reported event was 13 days, and 67.1% of events occurred within 30 days ^[1]. The authors concluded that most adverse events were reported soon after treatment began and wrote that this "suggest[s] the importance of closer monitoring during the first month of therapy" ^[1].

Why it matters for patients

FAERS is a voluntary reporting system, so the counts in this study reflect what was reported, not how often a problem actually occurs among everyone taking the drug ^[1]. A "signal" means a side effect showed up more often than expected in that database; it is not proof that the drug caused it. The analysis also cannot say how many people took tirzepatide during the study period, so it does not produce a risk percentage for any individual.

The practical takeaways are narrower. First, if medication errors are the leading signal, the friction points may be in how the drug is prescribed, dispensed, dosed or injected rather than in the drug's biology — though the abstract does not say what kinds of errors were reported or whether anyone was harmed ^[1]. Second, most reports clustered in the first month, which is when people are typically starting or stepping up treatment ^[1]. Third, injection-site reactions were among the strongest signals, a local issue rather than a whole-body one.

The authors reported no conflicts of interest ^[1].

What is not yet known

The abstract does not break the results out by brand, so it is not known whether reports differed between Mounjaro and Zepbound, or by dose, age group or reason for use. It also does not state whether FDA has reviewed these signals, whether labeling changes are planned, or whether any follow-up study is under way ^[1]. No timeline for next steps has been disclosed.