Tirzepatide and ketoacidosis: FAERS signal

A new pharmacovigilance analysis of FDA post-marketing reports finds a statistical signal linking tirzepatide to starvation ketoacidosis, with a reporting odds ratio of 70.3^[1]. The study, published in Endocrine Practice on June 4, 2026, used disproportionality analysis of the FDA Adverse Event Reporting System (FAERS) database through March 2026 to identify ketoacidosis-related signals associated with the dual GIP/GLP-1 receptor agonist.

What the FAERS data show

Researcher Connor Frey at the University of British Columbia analysed FAERS reports filed against tirzepatide and ran standard disproportionality metrics: the proportional reporting ratio (PRR) and the reporting odds ratio (ROR). Starvation ketoacidosis produced the strongest signal, with a PRR of 70.2 and an ROR of 70.3 (95% CI 46.9 to 105.2)^[1]. Ketosis not otherwise specified and euglycemic diabetic ketoacidosis (DKA) also met the statistical thresholds for a disproportionality signal, though at lower magnitudes.

These numbers mean that starvation ketoacidosis appears in tirzepatide-associated reports far more often than would be expected if the drug's report profile matched the database average. A high ROR does not prove that tirzepatide causes the condition. It flags a pattern worth investigating further.

Why the connection is biologically plausible

Tirzepatide suppresses appetite through GIP and GLP-1 receptor activation in the hypothalamus. In some patients, particularly those who reduce caloric intake sharply or experience prolonged nausea and vomiting during dose escalation, the body shifts to burning fat for fuel. When fat metabolism outpaces the liver's capacity to process the resulting ketone bodies, the blood becomes acidic. That is starvation ketoacidosis^[1].

The euglycemic variant is especially easy to miss. Blood glucose stays normal or low, so the classic diabetic-ketoacidosis red flag of hyperglycaemia never appears. A clinician who checks glucose alone and sees a normal reading may not think to test ketones. The FAERS signal for euglycemic DKA, while weaker than the starvation-ketoacidosis signal, reinforces that point.

A 2024 case series in the American Journal of Case Reports described four nondiabetic women aged 17 to 34 who developed hypoglycemic ketoacidosis after dose escalation to 5 mg of tirzepatide. All four presented with gastrointestinal symptoms, low blood glucose, high anion gap metabolic acidosis, and ketosis requiring hospitalisation^[2]. Each patient recovered after intravenous fluids and dextrose, but the cases illustrate how quickly the situation can escalate when caloric intake drops to near zero during the early weeks of treatment.

What the current drug label says

The Mounjaro prescribing information on DailyMed does not list ketoacidosis as a specific warning or adverse reaction^[3]. The label's adverse-event section focuses on gastrointestinal effects (nausea, diarrhoea, vomiting, constipation), pancreatitis, gallbladder events, and the boxed warning about thyroid C-cell tumours in rats. Ketoacidosis appears only in the pregnancy section as a background risk of poorly controlled diabetes, not as a drug-specific signal.

The gap between the FAERS signal and the current label is part of the study's point. The authors recommend that physicians counsel patients about ketoacidosis symptoms and maintain heightened vigilance for ketone testing in symptomatic tirzepatide users.

Limitations of FAERS analysis

FAERS is a voluntary reporting system. Reports do not require proof that the drug caused the event. Duplicate entries, missing data, and reporting bias (newer, high-profile drugs tend to attract more reports) all affect the numbers. A disproportionality signal is a hypothesis generator, not confirmation of a causal relationship. Controlled studies would need to establish how often tirzepatide users actually develop ketoacidosis compared to matched controls.

There is also a timing issue. Tirzepatide entered the market in 2022 and gained an obesity indication in late 2023. Newer drugs with heavy media coverage tend to attract more voluntary reports per prescription than older drugs do, inflating the apparent signal. The study does not adjust for prescribing volume, so the raw ROR should be read with that caveat in mind.

What this means for patients and clinicians

The practical takeaway from Frey's analysis is awareness, not alarm. Starvation ketoacidosis is rare but treatable when caught early. Patients on tirzepatide who experience persistent nausea, vomiting, abdominal pain, or an unusually sharp drop in appetite during dose escalation should know the warning signs: fruity-smelling breath, confusion, rapid breathing, and fatigue. A simple urine or blood ketone test at the point of care can confirm or rule out the diagnosis.

The study does not change the risk-benefit calculus for most patients. Tirzepatide remains one of the most effective approved therapies for type-2 diabetes and obesity, with a large trial programme behind it. But the FAERS signal adds starvation ketoacidosis to the list of outcomes clinicians should monitor for, particularly in patients who are eating very little during titration.

For more on tirzepatide's safety profile and regulatory status, see the tirzepatide overview and the regulation section. If you are taking tirzepatide and experiencing any of the symptoms described above, consult your prescribing clinician.