Combination Biologic and GLP-1 Receptor Agonist Therapy in Psoriasis

Key Takeaways

• Psoriasis and obesity are closely linked through shared inflammatory pathways, making weight management an increasingly important component of comprehensive psoriasis care.
• The phase 3b TOGETHER-PsO trial showed that combining ixekizumab with tirzepatide led to higher rates of complete skin clearance than ixekizumab alone.
• GLP-1–based therapies may improve psoriasis outcomes through both weight loss and potential anti-inflammatory effects.

The relationship between psoriasis and obesity is undeniable. Psoriasis was once viewed primarily as a dermatologic disease; however, it is now widely recognized as a systemic inflammatory condition associated with numerous comorbidities, including arthritis, inflammatory bowel disease, obesity, type 2 diabetes, cardiovascular disease, and the metabolic syndrome. Research has consistently demonstrated a bidirectional relationship between psoriasis and obesity, with excess adiposity contributing to systemic inflammation and worsening disease severity, while psoriasis itself may increase the risk of obesity through inflammatory and behavioral pathways.^1,2

Synthetic incretins, such as glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide-1 receptor agonists (GLP-1 RAs), are growing faster than almost any drug class in medical history. GLP-1 RAs (eg, semaglutide) and dual GLP-1/GIP RAs (eg, tirzepatide) have emerged as tools for weight management and offer simultaneous benefit in patients with concomitant psoriatic disease.³The recent TOGETHER-PsO trial evaluating concomitant ixekizumab and tirzepatide represents the strongest evidence to date supporting a holistic treatment strategy that addresses both psoriasis and obesity.⁴

THE PSORIASIS–OBESITY CONNECTION

Obesity is remarkably common among patients with psoriasis. Estimates suggest that 60% to 78% of patients with psoriasis are overweight or obese, and higher body mass index (BMI) has been associated with increased disease severity, reduced treatment response, and poorer overall outcomes.⁴

The biologic basis for this relationship is becoming increasingly better understood. Adipose tissue is not simply an energy storage organ; it is metabolically active and produces inflammatory cytokines, adipokines, chemokines, and complement factors that contribute to systemic inflammation.² These inflammatory signals may amplify pathways already implicated in psoriasis pathogenesis, creating a cycle in which obesity and psoriatic disease reinforce one another contributing to chronic disease.

Evidence predating the development of modern GLP-1 RAs demonstrated that weight reduction alone can improve psoriasis severity and enhance response to systemic therapy. As a result, many Dermatology providers now view weight management as an important adjunct therapy to systemic treatments for psoriasis rather than viewing obesity as an independent health issue. Additional real-world evidence has also demonstrated significant improvements in body weight, glycemic parameters, lipid profiles, and visceral adiposity among patients with psoriasis and obesity treated with tirzepatide while maintained on ixekizumab therapy.⁵

A NEW TREATMENT PARADIGM AFTER TOGETHER-PSO

The Phase 3b TOGETHER-PsO trial is the first large, randomized study designed specifically to address treatments for psoriasis and obesity concurrently.⁴ Adults with moderate-to-severe plaque psoriasis who were overweight (BMI ≥27 to <30) plus one or more weight-related comorbidities or obese (BMI ≥30) were randomized to receive either ixekizumab alone or ixekizumab and tirzepatide.⁴ Ixekizumab was administered via 80-mg injections: two at Week 0, one at Weeks 2, 4, 6, 8, 10, and 12, and one every 4 weeks thereafter.⁴ Tirzepatide was administered at 2.5 mg once weekly for 4 weeks, and the dose was increased by 2.5 mg every 4 weeks until the maximum tolerated dose of 5 mg, 10 mg, or 15 mg was achieved by Week 32.⁴

At week 36, 40.6% of patients receiving combination therapy achieved complete skin clearance (Psoriasis Area and Severity Index [PASI] 100), compared with 29.0% of patients receiving ixekizumab alone.⁴The full length of the randomized, open-label treatment period was 52 weeks.⁴

These findings suggest that addressing obesity may improve psoriasis outcomes beyond weight reduction alone. Whether the benefit is primarily the result of improved pharmacokinetics, reduced systemic inflammation, enhanced biologic responsiveness, or a combination of these factors remains unclear. However, the study provides compelling evidence that obesity management should be considered an integral component of psoriasis care rather than a parallel treatment goal. A similar study in psoriatic arthritis (TOGETHER-PsA) also found that combined ixekizumab and tirzepatide showed clinically meaningful improvements in joint disease and patient reported outcomes.⁶

WHY MIGHT OBESITY-TARGETED THERAPIES IMPROVE PSORIASIS?

The most predictable explanation for these results is reduction in BMI. Historically, heavier patients have often demonstrated lower response rates to biologic therapies, particularly with earlier approved agents such as tumor necrosis factor (TNF) inhibitors and ustekinumab. Even with highly effective modern biologics, the heaviest patients may still experience somewhat diminished efficacy compared with lower-weight counterparts.

However, emerging evidence suggests that GLP-1–related therapies may exert effects beyond weight reduction.3 Experimental and clinical data indicate that GLP-1 RAs may have immunomodulatory and anti-inflammatory properties. Several reviews have highlighted reductions in psoriasis severity, body surface area involvement, and quality-of-life measures among patients receiving GLP-1–related treatments, whether in combination with systemic psoriasis therapies or not.³

Although the weight loss agents do not directly target psoriasis-associated cytokines, such as IL-17 or IL-23, they may reduce the broader inflammatory milieu that contributes to disease activity. Further mechanistic and combination therapeutic studies are needed to clarify these pathways.

SHOULD DERMATOLOGISTS MODIFY BIOLOGIC THERAPY WHEN PATIENTS START GLP-1–RELATED TREATMENT?

There is little evidence to support routine modification of biologic therapy when a patient initiates a GLP-1–related treatment. Most psoriasis biologics have fixed, FDA-approved dosing regimens, with few antiquated weight-based exceptions. Ustekinumab dosing is weight dependent, and bimekizumab includes weight-related flexibility in certain circumstances with patients weighing more than 120 kg; but most IL-17, IL-23, and TNF inhibitors are administered at standard doses.

Similarly, there is currently no evidence supporting routine tapering of biologic therapy after successful weight loss. While weight reduction may improve treatment response, psoriasis remains a chronic systemic inflammatory disease associated with cardiovascular, oncologic, and musculoskeletal comorbidities. Maintaining disease control remains a priority even after metabolic improvement especially in the setting of psoriatic arthritis or skin findings predictive of developing joint involvement.⁷Still, future studies may help determine whether substantial and sustained weight loss influences long-term biologic requirements.

DISCUSSING WEIGHT MANAGEMENT WITH PATIENTS

For many dermatologists, discussing obesity can be more challenging than prescribing an immunomodulatory injectable biologic for an inflammatory skin condition. Conversations surrounding weight are often sensitive and require a patient-centered and individualized approach.

The goal should not be simply adding another medication. Weight management should be discussed within the broader framework of overall health improvement and disease control. Lifestyle interventions including nutrition, exercise, sleep optimization, and behavioral strategies remain important components of care, even when GLP-1–related pharmacotherapy is prescribed. If a dermatologists, nurse practitioner, or physician associate is not comfortable prescribing GLP-1–related therapy, they can refer patients to other clinicians with more expertise in that area. 

When considering GLP-1–related therapies, clinicians should also evaluate potential contraindications and risk factors, including personal or family histories relevant to medullary thyroid carcinoma or MEN2 syndromes, as well as factors that may increase pancreatitis risk. Most GLP-1 RAs come with a labeled black boxed warning of the risk of thyroid cancers, based on animal models and some postmarketing case reports in humans.⁸

THE IMPORTANCE OF MULTIDISCIPLINARY CARE