Eli Lilly and Company (NYSE: LLY) disclosed preliminary findings on Thursday from the ongoing TOGETHER-PsA open-label Phase 3b clinical trial, which investigates the simultaneous administration of Taltz (ixekizumab) and Zepbound (tirzepatide) compared to Taltz alone. This study targets individuals diagnosed with active psoriatic arthritis (PsA) and who are classified as obese or overweight with one or more related health conditions.
Psoriatic arthritis is an inflammatory condition associated with psoriasis, impacting joints and causing symptoms such as pain, stiffness, and characteristic skin and nail manifestations. The study's 36-week results indicate that the dual therapy of Taltz and Zepbound met the primary endpoint as well as all significant secondary endpoints, showing superiority over Taltz monotherapy.
Eli Lilly highlighted that TOGETHER-PsA represents the first controlled study to evaluate an incretin-based treatment alongside a biologic therapy for PsA. Specifically, the trial examined whether combining a monoclonal antibody targeting IL-17A with a dual GIP and GLP-1 receptor agonist offers enhanced clinical benefits for patients burdened by both psoriatic arthritis and weight-related issues.
Within the study cohort, 31.7% of participants receiving the combined Taltz and Zepbound therapy achieved at least a 50% improvement in PsA disease activity — a measure indicating reduction in joint inflammation and other PsA symptoms — along with a minimum 10% decrease in body weight. In contrast, only 0.8% of patients on Taltz alone met these criteria, thus fulfilling the trial's primary endpoint.
Moreover, one key secondary endpoint focused on ACR50 response rates, which reference a 50% improvement in tender and swollen joint counts along with other core measures of arthritis severity. Patients treated with the combination saw a 64% relative increase in achieving ACR50 compared to those on Taltz monotherapy (33.5% versus 20.4%, respectively). These results suggest that addressing the obesity factor with Zepbound can meaningfully alleviate the clinical burden of PsA.
The safety evaluation noted that adverse events experienced by participants on the combined regimen were generally mild to moderate in severity. Common side effects included gastrointestinal symptoms such as nausea, diarrhea, and constipation, as well as injection site reactions. The Taltz-only group predominantly experienced injection site reactions and upper respiratory infections. The observed adverse events were consistent with the established safety profiles of both therapeutic agents.
Taltz acts by binding selectively to the interleukin 17A (IL-17A) cytokine, obstructing its interaction with the IL-17 receptor and thereby reducing inflammation implicated in psoriatic arthritis. Zepbound is currently the only FDA-approved medication functioning as a dual agonist for glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 (GLP-1) receptors, designed to manage obesity.
In addition to TOGETHER-PsA, Eli Lilly is conducting the TOGETHER-PsO trial, exploring similar dual therapy benefits for patients with moderate to severe plaque psoriasis coupled with obesity or overweight. Topline results from this psoriasis-focused study are projected for release in the first half of 2026.
Following these disclosures, Eli Lilly's shares experienced a 0.72% increase, trading at $1,093.00 in premarket activity on Friday. The stock is nearing its 52-week peak of $1,133.95. Market data tracking tools highlight investor attention on the company’s therapeutic developments in immunology and metabolic diseases.