Eli Lilly and Co. (LLY) just gave doctors and patients a compelling reason to consider combination therapy for a particularly frustrating condition. On Thursday, the pharmaceutical giant released results from its TOGETHER-PsA trial showing that using Zepbound and Taltz together delivered substantially better outcomes than Taltz alone for people battling both psoriatic arthritis and weight issues.

Psoriatic arthritis, for context, is that unlucky combination condition where you get joint pain, stiffness, and a skin rash all tied to psoriasis. It's linked to weight-related inflammation, which makes the connection to obesity treatment particularly relevant here.

The Numbers Tell the Story

The topline data from this Phase 3b trial is striking. At 36 weeks, 31.7% of patients taking both Taltz (ixekizumab) and Zepbound (tirzepatide) hit the primary endpoint: a 50% improvement in psoriatic arthritis activity plus at least 10% weight reduction. Meanwhile, only 0.8% of patients on Taltz monotherapy achieved that same result. That's not a typo—less than one percent.

The secondary endpoints were equally impressive. The combination therapy delivered a 64% relative increase in patients achieving ACR50 compared to Taltz alone. Translation: 33.5% of combo therapy patients saw at least a 50% reduction in tender and swollen joints along with other core symptoms, versus 20.4% on Taltz by itself. This suggests that tackling obesity or overweight conditions with Zepbound actually reduces the burden of psoriatic arthritis.

Lilly emphasized that TOGETHER-PsA represents the first controlled study evaluating an incretin therapy used alongside a psoriatic arthritis biologic, making this genuinely new territory.

Safety Profile

As for safety, adverse events were generally mild to moderate and consistent with what's already known about each drug. The most common issues in the combination arm were nausea, diarrhea, constipation, and injection site reactions. For those on Taltz alone, injection site reactions and upper respiratory tract infections topped the list.

Taltz works as a monoclonal antibody that selectively binds with the interleukin 17A cytokine and blocks its interaction with the IL-17 receptor. Zepbound is the only FDA-approved dual GIP and GLP-1 receptor agonist for obesity management, hitting two metabolic pathways simultaneously.

Looking ahead, Lilly expects topline results from the related TOGETHER-PsO trial in the first half of 2026. That study is examining the same combination therapy in patients with moderate-to-severe plaque psoriasis and obesity or overweight.

Stock Movement: Eli Lilly shares traded up 0.72% at $1,093.00 during Friday's premarket session, hovering near the 52-week high of $1,133.95.