Yes, Stelara (ustekinumab) is an immunosuppressant, but it works differently from older drugs in that category. Rather than broadly dampening your entire immune system, Stelara is a biologic medication that targets two specific immune signaling proteins called IL-12 and IL-23. This makes it more precise than traditional immunosuppressants like methotrexate or azathioprine, though it still carries some of the same risks that come with dialing down immune activity.
How Stelara Suppresses the Immune System
Stelara is a lab-made antibody that locks onto a shared component of two proteins, IL-12 and IL-23, that your immune system uses to coordinate inflammatory responses. By binding to these proteins, Stelara physically blocks them from attaching to receptors on the surface of immune cells. Without that signal, the downstream chain reaction never fires: the immune cells don’t activate, don’t multiply as aggressively, and don’t produce the inflammatory chemicals that drive symptoms in autoimmune conditions.
The practical result is that Stelara dials down a specific branch of inflammation rather than suppressing the immune system across the board. It reduces production of several key inflammatory molecules, including ones responsible for the kind of chronic tissue damage seen in psoriasis and inflammatory bowel disease. This targeted approach is why Stelara is classified as a biologic immunosuppressant, distinct from conventional immunosuppressants that affect immune function more broadly.
Conditions Stelara Treats
The FDA has approved Stelara for six uses as of 2025:
- Moderate to severe plaque psoriasis in adults and children 6 and older
- Active psoriatic arthritis in adults and children 6 and older
- Moderately to severely active Crohn’s disease in adults
- Moderately to severely active ulcerative colitis in adults
In all of these conditions, the underlying problem is an immune system attacking the body’s own tissues. Stelara works by interrupting the specific immune pathways that drive that misdirected inflammation.
How the Infection Risk Compares
Because Stelara suppresses part of your immune response, it does increase susceptibility to infections. In clinical trials of children with psoriasis, serious infections occurred in about 1.8% to 2.3% of patients over 16 weeks, which is comparable to rates seen with other biologic therapies. For most people, this translates to a modestly elevated risk of common infections like upper respiratory infections or urinary tract infections, rather than frequent or dangerous ones.
The more specific concern relates to Stelara’s mechanism. People who are naturally born without functioning IL-12 or IL-23 are vulnerable to tuberculosis, salmonella, and certain other bacterial infections. Because Stelara blocks these same proteins, your doctor will test you for tuberculosis before starting treatment and will not prescribe it if you have an active infection of any kind. If latent TB is detected, it needs to be treated before Stelara can begin.
Cancer Risk in Long-Term Use
Any immunosuppressant raises theoretical concerns about cancer, since the immune system plays a role in detecting and destroying abnormal cells. The available data on Stelara is reassuring. A study tracking 341 patients with inflammatory bowel disease who already had a history of cancer found that Stelara did not increase the risk of new or recurrent cancers compared to patients receiving no immunosuppressive therapy. The hazard ratio was 0.88, meaning Stelara users had no statistically meaningful increase in cancer events over a median follow-up of about five years.
Vaccines and Stelara
Because Stelara suppresses immune function, live vaccines are off-limits during treatment. This includes the live shingles vaccine, the nasal flu spray, and BCG (used against tuberculosis in some countries). The BCG restriction is especially strict: you should not receive it for at least one year before starting Stelara or one year after stopping it. Even live vaccines given to people you live with require caution, since there’s a small theoretical risk of transmission.
Non-live vaccines, like flu shots and COVID vaccines, are safe to receive. However, your immune response to them may be weaker than normal, meaning they might not provide full protection. Ideally, you should be up to date on all recommended immunizations before starting treatment.
How Quickly It Works
Stelara’s onset depends on the condition being treated, but improvement can begin surprisingly fast. In Crohn’s disease trials, patients reported reduced stool frequency within one day of their first infusion, and all tracked symptoms showed measurable improvement by day 10. Clinical remission rates continued climbing over time: among patients who hadn’t failed previous biologic treatments, about 23% were in remission by week 3, rising to 55.5% by week 16. By week 44, up to two-thirds of patients were experiencing a clinical response.
For patients who had already tried and failed other biologic therapies, the numbers were lower but still meaningful, with remission rates climbing from about 13% at week 3 to 24% at week 16. Psoriasis patients typically see skin clearance begin within the first few weeks, with continued improvement over the first three to four months.
Targeted vs. Traditional Immunosuppression
If you’re comparing Stelara to older immunosuppressants you may have been prescribed before, the key difference is specificity. Traditional immunosuppressants suppress broad categories of immune cells or block cell division generally, which is effective but creates wide-ranging side effects. Stelara only blocks two cytokines out of the dozens your immune system uses, leaving most of your immune defense intact. This is why many patients tolerate it well over years of use, and why the infection rates in trials are relatively modest compared to some older therapies.
That said, “targeted” does not mean “harmless.” It is still an immunosuppressant by definition, still requires monitoring, and still means your body’s ability to fight certain infections is reduced. The benefit for people with autoimmune conditions is that the tradeoff is usually well worth it: the immune pathways Stelara blocks are the same ones causing disease, so suppressing them treats the problem at its source while leaving the rest of your immune system largely functional.