CATEGORY: GUT & DIGESTIVE HEALTH
A drug that has spent years clearing psoriasis plaques just posted its numbers in a different fight. In two linked phase 3 trials, half of the people with moderate to severe ulcerative colitis who kept taking guselkumab every four weeks were in remission a year in, against 19% of those switched to placebo.1 Ulcerative colitis is a disease in which the immune system attacks the lining of the large intestine, bringing bloody diarrhea, urgency and cramping that can rule a person’s calendar. Remission here wasn’t a vague word. It meant near-normal bathroom trips, no rectal bleeding and a colon lining that looked calm on camera.
Two Trials in One: 701 Started, 568 Went On
The QUASAR program ran in two stages. First, 701 adults whose disease was active despite other treatments received three intravenous infusions of guselkumab or a dummy infusion. Nobody chose their own arm, and nobody knew which they’d drawn. A computer dealt the assignments. By week 12, 23% on the drug were in remission versus 8% on placebo.1 That gap may look modest, but these were hard cases. Then came the second stage, the one that matters for a lifelong disease: 568 people who had responded were re-dealt into shots under the skin every four weeks, every eight weeks, or placebo. At week 44, remission stood at 50%, 45% and 19% respectively.1
Borrowed From the Skin, Aimed at the Colon
Guselkumab blocks interleukin-23, a chemical messenger that whips immune cells into attacking the body’s own tissue. In psoriasis, that attack lands on skin. In ulcerative colitis, it lands on the bowel wall, so the same blockade was a natural bet. It paid off well enough that US regulators approved the drug for ulcerative colitis in September 2024, and the trials behind that decision are what’s now published in full. Side effects in both stages looked much like placebo, with no cases of active tuberculosis, no severe allergic reactions and no serious liver injury reported.1 The studies were funded by Janssen, the company that sells the drug, which is standard for trials of this kind.
The Question the Trial Can’t Answer
What these results don’t say is whether guselkumab beats the other advanced options, because every comparison here was against placebo, not against another biologic (a drug made from living cells that targets specific parts of the immune system). Other advanced therapies used for ulcerative colitis include anti-TNF drugs (which block a different inflammatory protein called tumor necrosis factor), JAK inhibitors (which interrupt a signaling pathway inside immune cells), and integrin blockers (which keep certain immune cells from entering the gut lining). Each of these has shown benefit over placebo in its own trials, but head-to-head studies comparing them directly to guselkumab don’t yet exist. For someone whose colitis has shrugged off older drugs, that’s the obvious next question, and it stays open. What the trial does establish is that a third IL-23 blocker now has a year of controlled data in this disease, and that staying on the every-four-week dose kept half of responders in remission. For a condition people carry for decades, a year is the minimum worth talking about. It’s a start, not a finish line.
Key Takeaways
- Among people with moderate to severe ulcerative colitis who responded to guselkumab infusions, 50% on monthly shots were in remission at week 44, versus 19% of those moved to placebo.
- The evidence comes from placebo-controlled trials, so it shows the drug works, not how it ranks against other biologics such as anti-TNF drugs, JAK inhibitors, or integrin blockers for this disease.
- Side effects tracked closely with placebo across both trial stages, and the drug is FDA-approved for ulcerative colitis.
References
- Rubin DT, Allegretti JR, Panés J, et al. Guselkumab in patients with moderately to severely active ulcerative colitis (QUASAR): phase 3 double-blind, randomised, placebo-controlled induction and maintenance studies. The Lancet. 2025;405(10472):33–49. link