A new study analysis found that about 60 percent of participants with psoriatic arthritis (PsA) saw meaningful improvement in joint-related symptoms and quality of life after 16 weeks of treatment with guselkumab (Tremfya). These results build on earlier findings from the same study showing that nearly 3 out of 4 participants achieved clear or almost clear skin — regardless of their skin tone.

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These findings show that guselkumab can deliver high rates of skin clearance in a relatively short time for certain people, though everyone responds differently to medications.

Importantly, the study included people with a wide variety of skin tones, which is still rare in dermatology research. People with darker skin tones have long been underrepresented in psoriasis studies, even though they may experience more severe symptoms and face delays in diagnosis.

What Is Tremfya and How Does It Work?

First approved for treating psoriasis in 2017, guselkumab is a biologic medication approved to treat moderate to severe plaque psoriasis and active psoriatic arthritis. It’s given as an injection. It works by targeting a specific protein in the immune system called interleukin (IL)-23 that drives inflammation and causes psoriasis symptoms like plaques, itching, and the joint pain of PsA.

Inside the Study

The study included more than 200 adults with moderate to severe body or scalp psoriasis. Among them, 61 people (about 30 percent) also had PsA at the start of the study. Participants were randomly assigned to receive either guselkumab or a placebo (inactive treatment). Participants received three doses of guselkumab over 16 weeks.

In the most recent analysis, researchers assessed the impacts of PsA symptoms using the Psoriatic Arthritis Impact of Disease (PsAID-12) questionnaire, which measures physical, social, and emotional effects. Higher scores mean a greater impact on daily life.

At the beginning of the study, people with PsA were living with a heavy symptom burden. Their average score was 6.2 out of 10, and most were past the level that shows symptoms are well controlled. A PsAID-12 score of 3.95 or lower is considered “controlled.”

After 16 weeks, people taking guselkumab saw their PsAID-12 scores drop by an average of 3.5 points — a 56 percent improvement — compared with a drop of 0.8 points for people taking a placebo.

Among those who started with more severe symptoms, nearly 60 percent reached a controlled symptom state (a PsAID-12 score of 3.95 or lower) or achieved a clinically meaningful improvement of at least three points.

An earlier analysis of the study data, focused on skin symptoms, found:

• Seventy-four percent achieved clear or nearly clear skin.
• Fifty-seven percent saw at least a 90 percent improvement in psoriasis severity.
• People treated with guselkumab also experienced rapid relief from scalp psoriasis and improvements in itching, pain, and skin discoloration.

Researchers found no new side effects during the study. As with any medication, guselkumab can cause side effects. The most common ones include:

• Upper respiratory infections
• Headache
• Injection site reactions
• Joint pain
• Diarrhea
• Stomach flu
• Fungal skin infections
• Herpes simplex infections
• Bronchitis

Rare but serious side effects include severe allergic reactions and a higher risk of infections, as the medication can weaken the immune system.

A First-of-Its-Kind Focus on Diverse Skin Tones

What sets this study apart is its intentional design to include people with a wide variety of skin tones. The trial used tools like colorimetry to objectively assess skin tone and symptoms, reducing bias in how results were measured. It also featured clinical imagery and education resources tailored to skin of color, helping to improve diagnosis and care for underrepresented groups.

Historically, most dermatology images in medical textbooks have focused on lighter skin — only 4 percent to 19 percent of such books show conditions on darker skin tones. That can make it harder for both people and their doctors to recognize psoriasis early, especially when symptoms show up as purple, gray, or brown patches instead of the more commonly depicted red or pink plaques seen on lighter skin.

Why This Matters for Anyone With Psoriasis or PsA

For people living with psoriasis, these results offer reassurance that guselkumab and other treatments that target IL-23 may be effective, regardless of skin tone.

Equally important, the study helps raise the bar for how clinical trials should reflect the real-world population — especially in dermatology, where symptoms can look different on different skin types.

If you’re exploring treatment options for moderate to severe plaque psoriasis or PsA, talk with your dermatologist. They can help you weigh the benefits and risks of available treatments and find an approach that works for your skin, health, and lifestyle.

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On MyPsoriasisTeam, people share their experiences with psoriasis, get advice, and find support from others who understand.

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