Cosentyx (secukinumab) does affect your immune system, but it is not a broad-spectrum immunosuppressant in the traditional sense. It is classified as an interleukin-17A antagonist, a type of biologic that blocks one specific protein involved in inflammation rather than suppressing the immune system as a whole. That distinction matters because it shapes both the benefits and the risks you can expect while taking it.
How Cosentyx Works
Traditional immunosuppressants dampen large portions of your immune response. Cosentyx takes a much narrower approach. It is a lab-made antibody that latches onto a single inflammatory protein called IL-17A and prevents it from reaching its receptors on skin and joint cells. In conditions like psoriasis, IL-17A drives the rapid, painful skin cell turnover that produces plaques. By neutralizing just that one protein, Cosentyx interrupts the disease process without shutting down other major immune pathways.
At the doses used for psoriasis and arthritis, Cosentyx fully blocks IL-17A but does not neutralize the closely related protein IL-17F. It also leaves other immune cell functions intact, including the broader T-cell responses your body relies on to fight most infections. This selectivity is why researchers describe it as having fewer “off-target effects” compared to older, less precise treatments.
It Still Lowers Some Immune Defenses
Even though Cosentyx is targeted, it does reduce your body’s ability to fight certain types of infections. The FDA’s medication guide states plainly that Cosentyx “may lower the ability of your immune system to fight infections and may increase your risk of infections.” So while it is not a blanket immunosuppressant, calling it an immune-altering drug is accurate.
IL-17A plays a specific role in defending against fungal infections, particularly Candida (the yeast responsible for oral thrush and other mucosal infections). When IL-17A is blocked, your body produces fewer antimicrobial peptides that keep Candida in check, and the protective mucosal barriers in your mouth and gut become easier for yeast to penetrate. This is why yeast infections are the most distinctive infection risk with Cosentyx and other IL-17 inhibitors.
Serious infections are relatively uncommon. Pooled data from large clinical trials show a rate of serious infections around 1.9 per 100 patient-years for people with psoriatic arthritis and 1.2 per 100 patient-years for ankylosing spondylitis. A real-world Nordic study found that about 3.5% of patients on secukinumab were hospitalized for an infection in the first year. For context, the rate for adalimumab (a TNF inhibitor) in the same study was 1.7%, though pooled trial data for serious infections in psoriatic arthritis was actually higher with adalimumab at 2.8 per 100 patient-years. The overall picture is that infection risk exists but is modest for most people.
What Cosentyx Treats
The FDA has approved Cosentyx for six conditions:
- Moderate to severe plaque psoriasis in patients 6 years and older
- Active psoriatic arthritis in patients 2 years and older
- Ankylosing spondylitis in adults
- Non-radiographic axial spondyloarthritis in adults with objective signs of inflammation
- Enthesitis-related arthritis in children 4 years and older
- Moderate to severe hidradenitis suppurativa in adults
All of these are autoimmune or autoinflammatory conditions where the immune system attacks the body’s own tissues. Cosentyx calms that misdirected response without broadly suppressing immunity the way drugs like methotrexate or cyclosporine do.
Vaccines and Screening Before Starting
Because Cosentyx alters immune function, you should avoid live vaccines while taking it. The concern is that a weakened live virus in a vaccine could replicate more than intended when part of your immune response is blocked. Inactivated vaccines (like the standard flu shot) are considered safe to receive during treatment.
Before starting Cosentyx, your doctor will screen you for tuberculosis. All clinical trial participants were tested before enrollment using either a blood test or a skin test, and patients with active TB were excluded. If you have latent TB, it needs to be treated before you begin. Chest imaging is also typically part of the screening process.
Inflammatory Bowel Disease Risk
IL-17A also plays a role in gut health, and rare cases of new or worsening inflammatory bowel disease, including Crohn’s disease and ulcerative colitis, have occurred in people taking Cosentyx. If you already have a history of IBD, this is something to weigh carefully. Symptoms to watch for include persistent diarrhea, bloody stools, and abdominal pain.
Surgery and Pausing Treatment
If you are planning elective surgery, particularly joint replacement, current rheumatology guidelines recommend scheduling the procedure about five weeks after your last Cosentyx dose. Since Cosentyx is given every four weeks, this essentially means skipping one dose before surgery. Treatment can typically restart at least 14 days after surgery, once the wound is healing well and there are no signs of infection. Your surgical and rheumatology teams will coordinate the timing.
How It Compares to Traditional Immunosuppressants
Older immunosuppressants work by suppressing T-cells broadly, interfering with DNA replication in immune cells, or blocking multiple inflammatory pathways at once. These drugs are effective but carry higher risks of widespread immune suppression, including increased vulnerability to a wide range of bacterial, viral, and fungal infections.
Cosentyx sits in a different category. It is a biologic that targets one cytokine rather than the immune system at large. You are still more susceptible to certain infections, especially Candida, and you still need to take precautions around live vaccines and surgery. But the scope of immune suppression is meaningfully narrower. Think of it less as turning down the entire immune system and more as removing one specific gear from the inflammatory machinery driving your disease.