Retatrutide and UTIs: The Short Answer

Urinary tract infections (UTIs) were reported somewhat more often on retatrutide than on placebo in its Phase 3 trials. In TRIUMPH-1, the main obesity trial, 7.5% to 8.7% of participants on the three doses had a UTI during 80 weeks of treatment, against 5.3% on placebo, according to the full results published in the New England Journal of Medicine in September 2026. That works out to roughly 2 to 3.5 extra cases per 100 participants (our calculation from the paper's range and the company's per-dose figures). Of the infections reported, 92% occurred in women. They were generally mild or moderate, and none led to stopping treatment.

The other trials were less consistent. UTIs were more common than on placebo in TRIUMPH-3 (6.1% and 7.0%, against 5.3%) and in TRANSCEND-T2D-1 (up to 2.9%, against 0.0%), but in TRIUMPH-2, a trial in people with type 2 diabetes, only the highest dose had a higher rate than placebo (8.0%, against 6.6%). Neither the TRIUMPH-1 paper nor the company's announcements offer an explanation for the difference.

UTI Rates in Each Retatrutide Trial

Results have been reported from five Phase 3 trials. Four of them gave UTI rates for each dose:

The per-dose figures come from the company's announcements. For TRIUMPH-1, the published paper gives only a range, 7.5% to 8.7% across the three doses, so the announcement's 8.8% for 9 mg sits just above it; where the two differ, the paper's figure is the one to rely on. For TRIUMPH-2, the company's medical information page, which cites the paper published in The Lancet, gives rates of 3%, 5% and 8%, against 7% on placebo. Its 3% for 4 mg and 5% for 9 mg do not match the 3.8% and 6.3% in both announcements, and the page does not explain the difference. The fifth trial, TRIUMPH-4 in people with knee osteoarthritis, did not include UTIs in its announcement.

Three patterns stand out. First, in TRIUMPH-2, TRIUMPH-3 and TRANSCEND-T2D-1 the rates rose with the dose, but in TRIUMPH-1 they did not: the highest rate in the announcement was on 9 mg, not 12 mg. Second, where UTIs were more common on retatrutide, the gap was small, from under 1 to about 3.5 percentage points (our calculation). Third, in TRIUMPH-2, UTIs were less common on 4 mg and 9 mg than on placebo. In TRANSCEND-T2D-1, the percentages correspond to 1, 2 and 4 participants on 4 mg, 9 mg and 12 mg, out of 133 to 136 per group, and none of 134 on placebo (our calculation from the group sizes).

The trials enrolled different populations and ran for different lengths of time, so the rows are not directly comparable. Placebo rates alone ranged from 0.0% to 6.6%.

Why 92% of the UTIs Were in Women

The TRIUMPH-1 paper reports that 92% of the urinary tract infections occurred in women, and the investigators wrote in their discussion that the infections occurred almost exclusively in women. Women made up about two thirds of the trial: 1,533 of 2,339 participants, or 65.5% (our calculation from the paper's baseline table). Their share of the infections was therefore well above their share of the trial.

That fits what is known about UTIs in general. According to the US National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), bladder infections, the most common type of UTI, are more common in women than in men because of anatomy: the female urethra is short and close to the anus, which makes it easier for bacteria to reach the bladder. The institute adds that about half of all women develop a bladder infection at some point in their lives.

The main text of the TRIUMPH-1 paper does not give UTI rates for women and men separately on each dose, so it does not show how much more often women on retatrutide had UTIs than women on placebo.

How Serious Were the UTIs on Retatrutide?

In TRIUMPH-1, the published paper describes the urinary tract infections as generally mild or moderate and says they did not lead to treatment discontinuation. For TRIUMPH-1, TRIUMPH-2, TRIUMPH-3 and TRANSCEND-T2D-1, the company's announcements add that these events, reported together with dysesthesia, were generally mild to moderate and that the majority resolved during treatment.

The investigators also noted that the infections occurred without a clear temporal pattern. That sets them apart from the gastrointestinal side effects, which the same paper says occurred most commonly during dose escalation, when the dose was raised step by step. The full picture of adverse events in the trials is in retatrutide side effects.

Serious kidney problems were rare. The TRIUMPH-1 paper counts severe or serious acute kidney events as a separate category: 2 participants (0.3%) on 4 mg, none on 9 mg, 2 (0.3%) on 12 mg and none on placebo. It does not say whether any of them were connected to a UTI. The 48-week Phase 2 trial, published in 2023, reported renal events, without specifying their severity, in 3 of 267 participants on retatrutide and 1 of 70 on placebo.

Why Would Retatrutide Affect UTIs? What the Trials Show

The trials were not designed to find out why UTIs were more frequent, and neither the TRIUMPH-1 paper nor the company's announcements propose a cause. Trials count every adverse event that occurs during treatment, whether or not the drug caused it, which is why placebo groups report UTIs too. Five findings frame the question:

• The infections were concentrated in women. 92% of the TRIUMPH-1 infections occurred in women, in line with the higher background risk of bladder infections in women.
• The link with dose was inconsistent. Rates rose with the dose in TRIUMPH-2, TRIUMPH-3 and TRANSCEND-T2D-1, but were similar on 4 mg, 9 mg and 12 mg in TRIUMPH-1. In TRIUMPH-2, the two lower doses were below placebo.
• It did not cluster in the dose-escalation period. The TRIUMPH-1 investigators found no clear temporal pattern, unlike the gastrointestinal side effects.
• Fluid loss is a known issue for the drug class, but in connection with the kidneys, not infection. The US labels of tirzepatide and semaglutide warn about acute kidney injury due to volume depletion, mostly in people whose nausea, vomiting or diarrhea led to dehydration. Neither label links this to urinary tract infections, and the TRIUMPH-1 paper reports no analysis of fluid intake and UTIs.
• Background rates varied widely. The NIDDK lists diabetes among the conditions that make bladder infections more likely. Yet the two trials limited to people with type 2 diabetes, TRIUMPH-2 and TRANSCEND-T2D-1, had the highest and lowest placebo rates of the four, 6.6% and 0.0%.

Do Semaglutide and Tirzepatide Cause UTIs?

Urinary tract infections are not among the common adverse reactions listed for adults in the US labels of either drug. Tirzepatide's label, revised in August 2026, lists the adverse reactions reported in at least 2% of patients and more often than on placebo in its two main weight-loss trials; UTIs are not on that list. Semaglutide's label, revised in June 2026, uses the same threshold for its adult weight-loss trials, and UTIs are not on that list either. They do appear in semaglutide's trial in adolescents aged 12 and older: 4% on semaglutide, against 2% on placebo.

Absence from these tables does not mean no UTIs occurred; it means they did not meet the threshold of at least 2% and more frequent than placebo. On the same yardstick, the TRIUMPH-1 rates for retatrutide would qualify (our comparison). These are comparisons across separate trials and sources, not head-to-head results. How the three drugs compare on weight loss and other side effects is covered in retatrutide vs tirzepatide vs semaglutide.

What Is Still Unknown About Retatrutide and UTIs

The published data leave several questions open:

• UTI rates for women and men on each dose, compared with placebo within each sex.
• Whether infections recurred in the same participants, and how many were bladder infections and how many kidney infections.
• What happened after 80 weeks. The TRIUMPH-1 paper reports safety through week 80 and the 4-week follow-up, not for the extension to 104 weeks.
• Per-dose figures from the published TRIUMPH-2 and TRANSCEND-T2D-1 papers; this article relies on the company's announcements for those trials.

Longer studies are under way. TRIUMPH-Outcomes (NCT06383390) is evaluating cardiovascular and kidney outcomes, and how much is known about retatrutide's safety over time is covered in retatrutide long-term safety.

Retatrutide Sold Online: Why the Trial Data Don't Apply

Retatrutide has no approved dose or label, and its developer says it is legally available only through its clinical trials. Its current regulatory position is tracked in retatrutide approval status. The company says anything sold to consumers outside those trials is illegal, and warns that illicit retatrutide products may contain "unknown ingredients, harmful contaminants and impurities." The UTI rates above come from trials run under medical supervision and say nothing reliable about what those products might do.

Sources

• Jastreboff AM, Kaplan LM, Davies MJ, et al. Retatrutide, a Triple Hormone Receptor Agonist, for Treatment of Obesity. N Engl J Med. Published September 29, 2026. DOI: 10.1056/NEJMoa2604169. (TRIUMPH-1)
• Jastreboff AM, Kaplan LM, Frías JP, et al. Triple–Hormone-Receptor Agonist Retatrutide for Obesity — A Phase 2 Trial. N Engl J Med. 2023;389(6):514–526. DOI: 10.1056/NEJMoa2301972.
• Eli Lilly. Lilly's triple agonist, retatrutide, delivered powerful weight loss in pivotal Phase 3 obesity trial. May 21, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, drove substantial improvements in weight, A1C, knee osteoarthritis pain, and obstructive sleep apnea, demonstrating its remarkable potential to treat obesity and its complications. June 6, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, successful in two additional Phase 3 obesity trials, delivering significant improvements in weight and A1C. July 23, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, delivered substantial weight loss and A1C reduction, underscoring its potential promise for people with obesity and type 2 diabetes. September 29, 2026.
• Eli Lilly. Lilly's triple agonist, retatrutide, delivered weight loss of up to an average of 71.2 lbs along with substantial relief from osteoarthritis pain in first successful Phase 3 trial. December 11, 2025.
• Lilly Medical. Did participants with obesity experience urinary tract infections during the retatrutide TRIUMPH clinical trials? Last reviewed August 20, 2026.
• Lilly Medical. What are the results of monotherapy retatrutide in patients with type 2 diabetes from TRANSCEND-T2D-1? Last reviewed May 18, 2026.
• Eli Lilly. What to know about retatrutide. Last updated September 2026.
• Eli Lilly. US prescribing information for tirzepatide for weight reduction, sections 5.3 and 6.1. Revised August 2026.
• Novo Nordisk. US prescribing information for semaglutide injection and tablets for weight reduction, sections 5.5 and 6.1. Revised June 2026.
• National Institute of Diabetes and Digestive and Kidney Diseases. Definition & Facts of Bladder Infection in Adults. Last reviewed April 2024.

Medical Disclaimer: This article is for informational purposes only and is not medical advice. Retatrutide is investigational and is not approved by the FDA for any use. It is not available by prescription, and Lilly says anything sold to consumers under its name outside its clinical trials is illegal. The figures described here are those reported in clinical trials under medical supervision.