Stelara is not a TNF inhibitor. It belongs to a different class of biologic drugs entirely. While TNF inhibitors block a protein called tumor necrosis factor alpha, Stelara (ustekinumab) works by blocking two different proteins: interleukin-12 (IL-12) and interleukin-23 (IL-23). These are separate immune system signals that drive inflammation through different pathways. The distinction matters because it affects which conditions each drug treats best, what side effects to expect, and what options remain if one class stops working.
How Stelara Actually Works
Stelara is a human monoclonal antibody that targets a shared building block of IL-12 and IL-23, called the p40 subunit. By binding to this subunit, Stelara prevents both of these cytokines from attaching to their receptors on immune cells. This disrupts two specific arms of the immune response: one driven by Th1 cells (activated by IL-12) and another driven by Th17 cells (activated by IL-23). Both of these immune cell types contribute to the chronic inflammation seen in conditions like psoriasis and inflammatory bowel disease.
TNF inhibitors, by contrast, neutralize tumor necrosis factor alpha, a broadly inflammatory protein that acts earlier and more widely in the immune cascade. Because Stelara and TNF inhibitors target completely different molecules, they are classified as separate drug classes and can sometimes be used sequentially when one fails.
Which Drugs Are TNF Inhibitors
The FDA recognizes five TNF inhibitors currently on the market:
- Remicade (infliximab)
- Enbrel (etanercept)
- Humira (adalimumab)
- Cimzia (certolizumab pegol)
- Simponi (golimumab)
Stelara does not appear on this list. It is formally classified as an interleukin-12 and interleukin-23 antagonist, making it the first drug in its class when it was originally approved.
What Stelara Is Approved to Treat
Stelara is FDA-approved for several inflammatory conditions in adults: moderate to severe plaque psoriasis, active psoriatic arthritis, moderately to severely active Crohn’s disease, and moderately to severely active ulcerative colitis. It is also approved for children aged 6 and older with moderate to severe plaque psoriasis or active psoriatic arthritis. There is significant overlap with TNF inhibitors here, as drugs like Humira and Remicade also treat many of these same conditions, which is part of why people often confuse the two classes.
Stelara vs. TNF Inhibitors for Crohn’s Disease
A real-world study comparing Stelara to Humira (adalimumab) in Crohn’s disease found that Humira produced higher response rates overall. About 73% of patients starting Humira achieved a clinical response, compared to 50% of those starting Stelara. Remission rates followed a similar pattern: 44% for Humira versus 28% for Stelara.
Context matters here, though. In that same study, when researchers looked only at patients who had already tried and failed a TNF inhibitor, the results flipped. Stelara produced a clinical response in 52% of TNF-experienced patients compared to just 25% for those trying a second TNF inhibitor. Neither difference reached statistical significance in this smaller subgroup, but the trend highlights why Stelara is often positioned as a next step after TNF failure rather than a first-line biologic.
Lower Infection Risk With Stelara
One practical advantage Stelara holds over TNF inhibitors is a somewhat better safety profile when it comes to infections. A large comparative analysis found that Stelara was associated with a 7% lower risk of infection compared to TNF inhibitors in patients with inflammatory bowel disease. There was also a trend toward fewer infection-related hospitalizations, though that finding didn’t quite reach statistical significance.
Five-year follow-up data from Stelara’s clinical trials in Crohn’s disease showed that serious infections were uncommon, occurring in about 3.9% of patients, a rate similar to what was seen in placebo groups. TNF inhibitors, by contrast, have consistently shown an increased risk of infections compared to placebo in pooled analyses. The most common infections across both drug classes are respiratory and urinary tract infections. Opportunistic infections like Candida accounted for fewer than 5% of infections in either group.
Switching From a TNF Inhibitor to Stelara
Stelara is increasingly used in patients whose disease stopped responding to a TNF inhibitor. This is one of the key practical reasons the distinction between drug classes matters: because Stelara works through a completely different mechanism, it can still be effective even when TNF blockade has failed. A patient who loses response to Humira or Remicade has the option of trying a different TNF inhibitor or switching to a different class like Stelara.
For Crohn’s disease patients who require surgery while on a TNF inhibitor, recent research has compared continuing the same TNF inhibitor after surgery versus switching to Stelara. A retrospective study found no significant difference between the two strategies. The two-year clinical recurrence-free rate was 83% for those who continued their TNF inhibitor and 60% for those who switched to Stelara, but this difference was not statistically significant. Endoscopic recurrence rates were also comparable. This suggests that switching to Stelara after surgery is a reasonable option, particularly for patients whose TNF inhibitor wasn’t fully controlling their disease before the operation.