Tremfya (Guselkumab) for Crohn's Disease: A Patient Guide

Tremfya (guselkumab) became the first IL-23 inhibitor to earn FDA approval for moderately to severely active Crohn's disease with a choice of both subcutaneous and intravenous induction, giving patients and gastroenterologists a flexibility that no other drug in this class currently offers (1). If you have been weighing your biologic options or wondering whether there is something beyond your current treatment, this guide walks through what the clinical evidence actually shows, how dosing works in practice, and what to discuss with your care team.

Key Takeaways

• Tremfya for Crohn's disease was FDA-approved on March 20, 2025, and it is the only IL-23 inhibitor that offers both subcutaneous and intravenous induction pathways (1).
• In the GRAVITI trial, 56.1% of patients on guselkumab reached clinical remission at week 12, compared with 21.4% on placebo (2).
• Week 48 maintenance data from GRAVITI showed sustained remission in 60-66% of patients, versus 17.1% on placebo (2).
• The GALAXI trials demonstrated guselkumab was superior to ustekinumab (Stelara) on all pooled endoscopic endpoints at week 48 (3).
• Antibodies to guselkumab formed in only 8.8% of participants, with just 1.1% developing neutralizing antibodies and no effect on efficacy (2).
• The most common side effects were respiratory tract infections, injection site reactions, headache, and abdominal pain (4).

What Is Tremfya (Guselkumab) and How Does It Work?

Guselkumab is a fully human monoclonal antibody that blocks interleukin-23 (IL-23), one of the key chemical messengers driving inflammation in the gut. By binding to the p19 subunit of IL-23, Tremfya shuts down a signaling cascade that otherwise fuels the tissue damage many of us know all too well during a flare.

The IL-23 Pathway in Crohn's Disease Inflammation

IL-23 sits upstream of several other inflammatory signals, including IL-17 and IL-22. When IL-23 is overactive, it pushes the immune system to produce these downstream messengers in excess, which recruit more immune cells to the intestinal wall and keep the cycle of inflammation going. Blocking IL-23 at the source can dampen multiple branches of that cascade at once, rather than targeting just one downstream effect.

As we explored in our overview of IL-23 inhibitors for Crohn's disease, this drug class has rapidly become one of the most promising avenues in IBD treatment.

How Tremfya Differs From Other Biologics

One question that comes up constantly in our community is how Tremfya compares to other biologics already on the market. Here is a simplified breakdown:

• Anti-TNFs (infliximab, adalimumab, certolizumab): Block tumor necrosis factor alpha, a broad inflammatory signal. Effective for many patients but carry risks of infections and loss of response over time.
• Anti-integrin (vedolizumab/Entyvio): Blocks immune cells from migrating into the gut. Gut-selective, which limits systemic side effects, but may take longer to work.
• IL-12/23 dual blocker (ustekinumab/Stelara): Blocks both IL-12 and IL-23. As we covered in our Stelara patient guide, it has a strong track record, but blocking IL-12 also reduces part of the immune defense that fights certain infections.
• Selective IL-23 blockers (guselkumab/Tremfya, risankizumab/Skyrizi): Target the p19 subunit of IL-23 alone, leaving the IL-12 pathway intact. This selective approach may preserve a broader range of immune defenses.
• JAK inhibitors (upadacitinib/Rinvoq): Oral pills that work inside cells. Fast acting, but carry distinct safety considerations including a class-wide boxed warning.

Tremfya's selective targeting of the p19 subunit means it blocks IL-23 without interfering with IL-12. In theory, and increasingly in clinical data, that selectivity translates into a favorable safety profile while still delivering strong efficacy. For a broader look at choosing among biologics, our best biologic decision guide covers the landscape in more detail.

FDA Approval and Clinical Trial Evidence

The FDA approved Tremfya for adults with moderately to severely active Crohn's disease on March 20, 2025, based on compelling data from three major trials: GRAVITI, GALAXI-2, and GALAXI-3 (1). This approval made Tremfya the first and only IL-23 inhibitor with both subcutaneous and intravenous induction options for Crohn's - a practical advantage that lets doctors tailor the start of treatment to each patient's needs.

The GRAVITI Trial: Subcutaneous Induction

GRAVITI enrolled 347 adults with moderately to severely active Crohn's disease and tested a fully subcutaneous induction and maintenance approach (2).

Induction results (week 12):

• Clinical remission: 56.1% on guselkumab vs. 21.4% on placebo
• Endoscopic response: 41.3% vs. 21.4%

Both results were highly statistically significant (P less than 0.001) (2).

Maintenance results (week 48):

• Clinical remission on 100 mg every 8 weeks: 60.0% vs. 17.1% placebo
• Clinical remission on 200 mg every 4 weeks: 66.1% vs. 17.1% placebo

These numbers tell a clear story: a strong majority of patients who responded to induction continued to do well nearly a year later, while the placebo group fell sharply (2).

The GALAXI-2 and GALAXI-3 Trials: IV Induction vs. Stelara

The GALAXI program combined more than 1,000 patients across two parallel phase 3 trials and included an active comparator arm against ustekinumab (Stelara) - something relatively rare in Crohn's trials and extremely valuable for making real-world treatment decisions (3).

At week 48, guselkumab was superior to ustekinumab on all pooled endoscopic endpoints:

• Endoscopic remission: 37.2% (guselkumab 200 mg) and 33.2% (guselkumab 100 mg) vs. 24.7% ustekinumab (3)

For patients and doctors deciding between the two, as we discussed in our Skyrizi vs. Stelara comparison, head-to-head data like this can make the conversation much more concrete than comparing across separate trials.

Two-Year Durability

While the published data focuses on 48-week endpoints, the consistency of remission rates from week 12 through week 48 suggests durable benefit. Longer-term data from extension studies and real-world registries will continue to build the picture, but what we have so far is encouraging.

Dosing and Administration Options

One of Tremfya's standout features for Crohn's disease is that it offers two distinct ways to start treatment. This flexibility matters because some patients have easy access to an infusion center, while others strongly prefer to handle everything at home.

Subcutaneous (SC) Induction Pathway

• Induction: 400 mg subcutaneous injection at weeks 0, 4, and 8 (three total injection visits) (2)
• This is a higher loading dose given under the skin, typically in the thigh or abdomen

Intravenous (IV) Induction Pathway

• Induction: Given by IV infusion at weeks 0, 4, and 8, with the dose based on body weight
• This takes place at an infusion center or hospital outpatient clinic

Maintenance Dosing (After Week 12)

Regardless of which induction path you follow, maintenance is the same:

| Option | Dose | Route | Frequency | |--------|------|-------|-----------| | Standard maintenance | 100 mg | Subcutaneous | Every 8 weeks | | Higher maintenance | 200 mg | Subcutaneous | Every 4 weeks |

Your gastroenterologist will help determine which maintenance schedule is right for you based on your response, disease severity, and preferences (2).

Practical Tips for Self-Injection

• Tremfya is stored in the refrigerator (2-8 degrees C). Take it out about 30 minutes before injecting to let it reach room temperature.
• Rotate injection sites between the front of your thighs, lower abdomen (avoiding 5 cm around the navel), and the back of the upper arms (if someone else is injecting).
• Many patients find that icing the site beforehand helps with discomfort.
• Your care team will walk you through the first self-injection, and manufacturer resources include demonstration videos.

Side Effects and Safety Profile

Understanding the safety data helps you have an informed conversation with your doctor. No medication is risk-free, and knowing what to watch for puts you in a stronger position.

Common Side Effects

In the Crohn's disease clinical trials, the most frequently reported adverse events with Tremfya compared to placebo were (4):

• Respiratory tract infections (upper and lower): up to 38.3% vs. 25.6% with placebo
• Abdominal pain
• Injection site reactions (redness, swelling, or discomfort at the injection site)
• Headache
• Fatigue
• Joint pain (arthralgia)
• Diarrhea
• Gastroenteritis (stomach bugs)

Most of these were mild to moderate in severity and did not lead to patients stopping the medication.

Serious Risks and Warnings

The prescribing information highlights several serious but uncommon risks (4):

• Hypersensitivity reactions: Including rare cases of anaphylaxis. If you develop difficulty breathing, swelling, or a widespread rash after an injection, seek emergency care immediately.
• Infections: Because Tremfya dampens part of the immune system, serious infections can occur. In Crohn's trials, active tuberculosis was reported in 2 patients. This is why TB screening (typically a blood test and sometimes a chest X-ray) is required before starting treatment.
• Drug-induced liver injury: Rare cases have been reported. Your doctor will check liver function tests before and during treatment.

Screening Before Starting Tremfya

Before your first dose, expect your gastroenterologist to order:

• Tuberculosis screening (QuantiFERON or PPD skin test)
• Hepatitis B and C testing
• A review of your vaccination history - live vaccines should be given before starting Tremfya, as they are not recommended during treatment
• Baseline blood work including liver function

Immunogenicity: Will Your Body Make Antibodies Against It?

One concern with any biologic is whether the body's immune system will recognize the drug as foreign and produce antibodies that reduce its effectiveness. The GRAVITI data on this front are reassuring: antibodies to guselkumab were detected in 8.8% of participants, but only 1.1% developed neutralizing antibodies (the kind that could interfere with the drug's action). Importantly, there was no observed impact on drug levels or clinical efficacy through week 48 (2).

This is a relatively low immunogenicity rate compared with some older biologics, and it is one of the reasons selective IL-23 inhibitors have generated so much interest.

Who Is a Good Candidate and How to Access Tremfya

Tremfya is approved for adults with moderately to severely active Crohn's disease who have had an inadequate response, intolerance, or lost response to conventional therapy (such as corticosteroids, immunomodulators) or biologic therapy (1). In practice, that means it is an option for a wide range of patients.

After Conventional Therapy or Biologic Failure

The GRAVITI trial enrolled patients who had failed conventional therapy as well as those who had failed one or more biologics, and guselkumab showed benefit across both groups (2). If you have tried anti-TNF medications (like infliximab or adalimumab), vedolizumab (Entyvio), or ustekinumab (Stelara) and they either stopped working or caused side effects you could not tolerate, Tremfya may be worth discussing with your gastroenterologist.

Switching From Stelara or Another IL-23 Inhibitor

A common question in our community is whether switching from Stelara to Tremfya makes sense. Since guselkumab targets IL-23 selectively (without blocking IL-12) and showed superiority over ustekinumab on endoscopic endpoints in the GALAXI trials (3), some gastroenterologists are recommending it for patients who have plateaued or lost response on Stelara. However, this is an individualized decision that depends on your specific disease activity, how long you have been on your current therapy, and your tolerance of the switch process.

Special Populations

• Pregnancy and breastfeeding: Data are limited. Monoclonal antibodies are known to cross the placenta, particularly in the third trimester. If you are planning a pregnancy or are currently pregnant, discuss the timing and risks with your GI team and obstetrician.
• Older adults: No specific age-related contraindications, but infection risk may be somewhat higher. Your doctor will weigh this against the benefit.

Insurance, Prior Authorization, and Patient Assistance

Like most biologics, Tremfya typically requires prior authorization from your insurance company. This means your gastroenterologist's office will need to submit documentation showing that you meet the criteria (usually prior treatment failures). The process can take days to weeks.

If cost or coverage is a barrier, the manufacturer (Janssen/Johnson & Johnson) offers a patient assistance program through Janssen CarePath. International patients should check with their national health system or treatment center, as availability and reimbursement vary by country.

Questions to Ask Your Gastroenterologist

Bringing a list of questions to your appointment can help you feel more confident in your treatment decision. Here are some to consider:

Before Starting Tremfya

• Am I a candidate given my disease location and prior treatment history?
• Would you recommend SC or IV induction for my situation, and why?
• Do I need to stop my current biologic before starting, and if so, how long should I wait?
• Should I combine Tremfya with an immunomodulator (like azathioprine or methotrexate)?

During Treatment and Monitoring Response

• How will we measure whether Tremfya is working - through symptoms, lab markers like calprotectin, endoscopy, or imaging like MRE?
• What is the timeline for seeing improvement, and when should we reassess?
• If I do not respond by week 12 or 24, what are the next steps?
• Are there any medications or supplements I should avoid while on Tremfya?

Frequently Asked Questions

Is Tremfya safe for long-term use in Crohn's disease?

Clinical trial data through 48 weeks show a consistent safety profile with no new safety signals emerging over time (2, 4). The most common side effects remain respiratory tract infections and injection site reactions. Longer-term extension studies are ongoing, and guselkumab has been used for psoriasis since 2017, providing additional safety experience in a different patient population.

How quickly does Tremfya start working for Crohn's symptoms?

In the GRAVITI trial, significant improvements were seen as early as week 12 of induction, with 56.1% of patients achieving clinical remission by that point (2). Some patients notice symptom relief within the first few weeks, but the full effect on inflammation and endoscopic healing often takes longer. Your doctor will typically assess your response around weeks 12-24.

Can I switch from Stelara to Tremfya?

Many gastroenterologists are considering this switch, particularly given that the GALAXI trials showed guselkumab was superior to ustekinumab on endoscopic endpoints (3). The logistics of switching - including timing and any washout period - should be discussed with your GI team. There is no one-size-fits-all answer, and your doctor will consider your current disease activity and treatment history.

What is the difference between the subcutaneous and IV induction?

Both pathways deliver guselkumab during the induction phase at weeks 0, 4, and 8. The SC pathway uses a fixed 400 mg dose given by injection under the skin, while the IV pathway delivers the drug by infusion at a weight-based dose (1, 2). After induction, both pathways transition to the same subcutaneous maintenance injections. The choice often comes down to whether you prefer the convenience of self-injection or the supervised setting of an infusion center.

Does Tremfya cause hair loss or weight gain?

Hair loss and weight gain were not listed among the common adverse events in the Crohn's disease clinical trials (4). If you experience unexpected changes in hair or weight while on treatment, discuss them with your healthcare provider, as they could be related to your underlying disease, nutritional status, or other medications.

Is Tremfya covered by insurance?

Most private insurance plans and many national health systems cover Tremfya for approved indications, but prior authorization is almost always required. Your gastroenterologist's office will typically handle the paperwork. If coverage is denied or your out-of-pocket costs are high, the Janssen CarePath program and independent foundations like the Patient Access Network Foundation may offer financial assistance. Coverage varies significantly by country.

Can I self-inject Tremfya at home?

Yes. After the induction phase (whether SC or IV), maintenance doses are given as subcutaneous injections that most patients learn to do at home. Your healthcare team will train you on proper injection technique, storage, and disposal during or after the induction period. Many patients find the process straightforward after one or two practice sessions.

References

1. Guselkumab Receives FDA Approval for Adults With Moderately to Severely Active Crohn Disease. Pharmacy Times, March 20, 2025. Read article
2. Efficacy and Safety of Guselkumab Subcutaneous Induction and Maintenance in Participants With Moderately to Severely Active Crohn's Disease: Results From the Phase 3 GRAVITI Study. Gastroenterology, 2025. Read study
3. Efficacy and safety of intravenous induction and subcutaneous maintenance therapy with guselkumab for patients with Crohn's disease (GALAXI-2 and GALAXI-3): 48-week results. The Lancet, 2025. Read study
4. FDA Approves Guselkumab (Tremfya) For Crohn Disease. HCPLive, 2025. Read article
5. A Study of Guselkumab Subcutaneous Therapy in Participants With Moderately to Severely Active Crohn's Disease (GRAVITI). ClinicalTrials.gov, NCT05197049. View trial
6. GALAXI 2 and 3: Guselkumab Superior to Ustekinumab for Crohn's Disease. HCPLive, 2025. Read article