What is guselkumab?
Guselkumab (brand name Tremfya) is a biologic medication used to treat psoriatic arthritis and plaque psoriasis. It is a self-injectable medication administered at home using the One-Press patient-controlled injector.
How it works
Guselkumab is a monoclonal antibody that targets the p19 subunit of interleukin-23 (IL-23) — the same target class as risankizumab (Skyrizi). IL-23 is a key upstream signal that drives the inflammatory pathways responsible for psoriatic disease. By blocking IL-23, guselkumab selectively reduces inflammation while leaving much of the immune system’s normal function intact.
How it’s given
Guselkumab is self-administered as a subcutaneous (under the skin) injection:
- Loading phase: 100 mg at week 0 and week 4
- Maintenance phase: 100 mg every 8 weeks
- For psoriatic arthritis, your rheumatologist may prescribe dosing every 4 weeks after the loading phase, depending on your response
Guselkumab does not need to be combined with methotrexate.
Storage: Keep guselkumab refrigerated. Allow it to reach room temperature before injecting.
What to expect when starting
- Skin improvement is often visible within 4 weeks
- Joint improvement typically takes 8 to 16 weeks to become noticeable
As with other IL-23 inhibitors, the medication’s selective mechanism means it may take a bit longer to reach full effect on joint symptoms compared to some other biologics, but the trade-off is an excellent safety profile and convenient dosing.
Side effects to watch for
Guselkumab is very well-tolerated overall. The most common side effects include:
- Upper respiratory infections (cold-like symptoms)
- Injection site reactions (mild redness or discomfort)
- Tinea infections (fungal skin infections such as athlete’s foot or ringworm)
Serious side effects are uncommon. Let your rheumatologist know if you develop signs of infection, a new or worsening rash, or any symptoms that concern you.
Required screening before starting
Before beginning guselkumab, your rheumatologist will order:
- Tuberculosis (TB) testing — standard for all biologic medications
Things to avoid
- Live vaccines should not be given while on guselkumab. Inactivated vaccines (such as the flu shot) are safe and recommended.
Good to know: Unlike IL-17 inhibitors (such as Cosentyx and Taltz), IL-23 inhibitors like guselkumab are safe for patients with inflammatory bowel disease. If you have a history of IBD or bowel symptoms, this is an important consideration in choosing a biologic.
Frequently asked questions
How is guselkumab different from risankizumab (Skyrizi)? Both target IL-23 (p19 subunit) and have similar efficacy and safety profiles. The main differences are dosing frequency — guselkumab is given every 8 weeks in maintenance, while risankizumab is given every 12 weeks. Your rheumatologist and insurance coverage may help determine which is the best choice.
Do I need to take methotrexate with guselkumab? No. Guselkumab is effective as a standalone treatment.
What about the fungal infection risk? Tinea (fungal) infections are generally mild and treatable with topical antifungal creams. Let your rheumatologist know if you notice any new rashes, especially between your toes or in skin folds.
What if I miss a dose? Inject the missed dose as soon as you remember, then resume your regular schedule. Contact your rheumatologist’s office if you are unsure.
How long will I need to take guselkumab? Guselkumab is typically a long-term treatment. If it is working and you are tolerating it well, your rheumatologist will generally recommend continuing. Stopping may lead to a return of symptoms.
This handout is for informational purposes only and does not replace the advice of your rheumatologist. Always discuss your specific medical situation, including all medications and health conditions, with your provider before starting or changing any treatment.