What Are the Side Effects of Secukinumab (Cosentyx)?

Secukinumab, sold under the brand name Cosentyx, causes side effects that are mostly mild to moderate, with upper respiratory infections, sore throats, and diarrhea topping the list in clinical trials. The drug works by blocking a specific immune-signaling molecule called interleukin-17A, which helps clear psoriasis, psoriatic arthritis, and ankylosing spondylitis but also leaves certain parts of the immune system slightly more exposed. That tradeoff shows up as a predictable set of risks that have been tracked across thousands of patients and several years of follow-up data.

The Most Common Side Effects

Across the pivotal trials that led to FDA approval, the side effects seen in at least 7% of patients (and more often than placebo) were nasopharyngitis, upper respiratory tract infection, and diarrhea. Nasopharyngitis alone showed up in roughly 11% to 29% of patients on secukinumab, compared with about 9% to 20% of people on placebo.¹ That wide range reflects variation across different trial populations: people with psoriasis, psoriatic arthritis, and ankylosing spondylitis sometimes had different rates. The point, though, is that the gap between drug and placebo for these respiratory infections is real but modest. Many people barely notice them, or they resolve without treatment.

Headaches and fatigue also come up in general clinical use, though they are less consistently highlighted across all trial datasets. A study specifically looking at secukinumab alongside vaccination in healthy subjects found headache to be the single most common complaint.²

Yeast Infections and Why They Happen

IL-17A plays a genuine role in your body’s defense against fungi, particularly Candida species. When you block it, mucosal surfaces like the mouth, throat, and genital area become a bit more vulnerable to yeast overgrowth. This makes Candida infections one of the more mechanistically predictable side effects of secukinumab and other drugs in its class.³

In pooled long-term data across psoriasis, psoriatic arthritis, and ankylosing spondylitis, the rate of Candida infections was about 2.2, 1.5, and 0.7 per 100 patient-years, respectively.⁴ Those numbers mean roughly two out of every hundred psoriasis patients per year of treatment develop some kind of yeast infection. The reassuring detail is that across all clinical trials, these infections stayed localized, ranged from mild to moderate in severity, and did not force anyone to stop the medication.⁵ Oral thrush or a vaginal yeast infection might need a short course of antifungal treatment, but they are not a reason to abandon secukinumab in most cases.

Inflammatory Bowel Disease

This is the side effect that gets the most attention in rheumatology and dermatology clinics, especially because the patients taking secukinumab already have inflammatory conditions that share genetic and immune overlap with Crohn’s disease and ulcerative colitis. IL-17A has a complicated role in the gut: while it drives inflammation in the skin and joints, it also helps maintain the intestinal barrier. Blocking it can, in a small number of people, tip the gut toward inflammation rather than away from it.

A pooled analysis of 21 clinical trials covering over 7,300 patients found 41 total cases of inflammatory bowel disease, about 0.56% of exposed patients. Most were new-onset. The rate was highest in people with ankylosing spondylitis, a group already known to be at elevated baseline risk for gut inflammation.⁶ Case reports have further documented individual patients developing Crohn’s disease during treatment, with gastroenterologists attributing the onset to the drug.⁷

The practical takeaway is that secukinumab is generally avoided in people who already have inflammatory bowel disease, and clinicians watch for new gastrointestinal symptoms like persistent diarrhea, abdominal pain, or bloody stools. The absolute risk is low, but it is not theoretical.

Serious Infections and Opportunistic Risks

The rate of serious infections stayed consistently low in pooled long-term data: about 1.4 per 100 patient-years in psoriasis, 1.9 in psoriatic arthritis, and 1.2 in ankylosing spondylitis.⁸ These are serious enough to require hospitalization or IV antibiotics, but they are uncommon. Five-year follow-up data showed no increase in opportunistic infections over time, with the incidence staying below 0.2 per 100 patient-years, and no tuberculosis reactivation was reported.⁹

A massive post-marketing safety analysis covering a full million patient-years of exposure identified only 52 cases classified as potentially clinically significant opportunistic infections, and the majority of those were either poorly documented or likely related to the patient’s underlying conditions rather than the drug itself.¹⁰ A million patient-years is an enormous denominator, and the rarity of these events in that data set is genuinely reassuring.

Hepatitis B Reactivation and Tuberculosis Screening

Before starting secukinumab, you will be screened for latent tuberculosis and hepatitis B. The tuberculosis concern is largely theoretical at this point: no cases of TB reactivation appeared in the pooled trial data.¹¹ A study specifically tracking patients with latent TB who took secukinumab found zero reactivations, whether or not they received preventive TB treatment.¹²

Hepatitis B is a slightly different story. The same study found that about 16% of patients with concurrent hepatitis B infection experienced viral reactivation after an average of nine months on secukinumab, and the risk was concentrated in people who were not receiving antiviral prophylaxis.¹³ A separate Korean cohort study reported no reactivation at all among hepatitis B carriers managed with antiviral prophylaxis, reinforcing the idea that the risk is manageable when monitoring and prevention are in place.¹⁴ The bottom line is that if you carry hepatitis B, secukinumab is not off the table, but your doctor will likely want you on antiviral prophylaxis and will monitor your viral load regularly.

Cardiovascular Safety and Cancer Risk

Psoriasis itself is associated with higher cardiovascular risk, which means any long-term treatment gets scrutinized for heart-related effects. In the clinical trial data, major adverse cardiovascular events (heart attack, stroke, cardiovascular death) stayed below 0.7 per 100 patient-years across all three conditions, with no apparent increase over time.¹⁵ A meta-analysis of randomized controlled trials across multiple biologic drug classes found no statistically significant increase in cardiovascular events with IL-17A blockers like secukinumab.¹⁶

On the cancer front, the overall malignancy rate was about 1 per 100 patient-years or lower.¹⁷ The most frequently reported malignancies were basal cell carcinoma and squamous cell carcinoma, two common skin cancers in the general population that are also more frequently diagnosed in people with chronic inflammatory skin conditions. A dedicated analysis found basal cell carcinoma at a rate of about 0.24 per 100 patient-years across indications, and squamous cell carcinoma much lower at about 0.05 per 100 patient-years.¹⁸ These rates did not climb over time, and they are in line with what would be expected in a population with chronic inflammatory disease.

Paradoxical Skin Reactions

One of the stranger things biologics can do is trigger immune reactions that look like the opposite of what they are supposed to treat. With secukinumab, case reports describe patients developing atopic dermatitis (eczema) while being treated for psoriasis. The proposed explanation involves the immune system’s competing inflammatory pathways: when you suppress the pathway driving psoriasis, the pathway associated with eczema can flare up in certain predisposed individuals.¹⁹ Delayed-type drug hypersensitivity reactions have also been documented, with at least one case involving a psoriasiform skin eruption developing days after a secukinumab injection in a patient being treated for hidradenitis suppurativa.²⁰

These paradoxical reactions are rare enough that they show up as individual case reports rather than in pooled trial data. They are worth knowing about mainly because they can be confusing: your skin condition appears to worsen or change character, and it can be hard to tell whether the disease is progressing or the drug itself is causing a new problem. If your skin develops a rash that looks different from your original condition after starting secukinumab, mentioning it to your dermatologist quickly is important.

How the Body Responds to the Drug Itself

Because secukinumab is a monoclonal antibody (a large protein injected into the body), there is always a question of whether the immune system will develop antibodies against it. This phenomenon, called immunogenicity, is one reason biologics sometimes lose effectiveness over time. Secukinumab performs well here: in a study of over 2,800 patients, only about 0.4% developed treatment-emergent anti-drug antibodies. Even in those few patients, the antibodies were not associated with loss of drug response or with injection-site reactions through a full year of follow-up.²¹ A review of secukinumab in ankylosing spondylitis confirmed this, noting that in the small minority who developed anti-drug antibodies, neither efficacy nor adverse events were affected.²²

This is actually a practical advantage of secukinumab relative to some other biologics. Some older drugs in the TNF-inhibitor class have higher immunogenicity rates, which is one reason patients sometimes need to combine them with methotrexate to keep antibody formation at bay. With secukinumab, that concern is minimal.

Blood Counts and Lab Monitoring

Because IL-17A plays a role in immune cell signaling, questions have come up about whether blocking it affects white blood cell counts, particularly neutrophils (the immune cells most involved in fighting bacterial infections). A study tracking complete blood counts and standard metabolic markers at baseline and six months into treatment found no significant changes in any parameter, including white blood cells, liver enzymes, kidney function markers, or inflammatory markers. Hemoglobin actually went up slightly in patients who stayed on the drug, likely reflecting improved control of chronic inflammation rather than a direct drug effect.²³ Mild, transient drops in neutrophil count have been reported in prescribing information, but clinical data do not suggest this translates into increased infection risk or requires routine blood monitoring beyond what clinicians already do.

Safety in Children and Adolescents

Secukinumab is approved for pediatric plaque psoriasis, and safety data in kids now stretches to four years. In a phase III trial following children and adolescents over roughly 314 patient-years, the safety profile matched what has been seen in adults, with no new red flags emerging. No deaths were reported. Serious adverse events were uncommon and included things like COVID-19, appendicitis, and tonsillitis, which are common in the pediatric age group regardless of medication. Importantly, no impact on growth, development, or sexual maturation was observed.²⁴

A separate trial out to 236 weeks found that the most common side effects in children were nasopharyngitis, headache, and tonsillitis, with only three Candida infections reported across the entire study.²⁵ The 52-week results from the same trial confirmed the pediatric safety profile was consistent with adults and carried no new safety signals.²⁶ For parents weighing the risks, the evidence suggests that the pediatric safety profile genuinely mirrors the adult one rather than introducing unique concerns.

Older Adults and Multiple Medications

Elderly patients with psoriasis tend to have more comorbidities, take more medications, and have been through multiple failed treatments. That combination raises legitimate concern about tolerability. A two-year real-world study in elderly patients found that side effects rarely led to discontinuation, with only one patient out of about 30 stopping because of adverse events.²⁷ A post-hoc analysis of a larger study compared the frequency of treatment-emergent adverse events in older versus younger patients and found them essentially identical, at about 17% versus 15%.²⁸ Age alone does not appear to meaningfully change the drug’s safety profile.

Pregnancy

Data here is thin, as it usually is with newer biologics. Secukinumab is generally avoided in pregnancy when possible, and the prescribing information reflects limited human data. That said, at least one detailed case report describes a patient with pustular psoriasis who took secukinumab through two consecutive pregnancies. Both pregnancies resulted in healthy infants with no observed immune abnormalities, and the babies responded normally to live attenuated vaccines, suggesting that maternal secukinumab did not meaningfully suppress their immune function.²⁹ A case report is obviously not the same as a controlled trial, but for patients who become pregnant while on secukinumab or who have severe disease that demands treatment during pregnancy, the available reports are reassuring rather than alarming.

How Secukinumab Compares to Other Biologics for Side-Effect Tolerability

Patients and clinicians often want to know not just whether secukinumab is safe in absolute terms but how it stacks up against alternatives. A large drug-survival study comparing several common biologics for psoriasis found that secukinumab, guselkumab, and ustekinumab had similar safety-related drug survival curves, meaning patients were equally likely to remain on these drugs without needing to stop for side effects. Adalimumab and ixekizumab, by comparison, had lower safety-related survival, meaning more people stopped those drugs because of adverse events.³⁰

In real-world practice, secukinumab’s drug survival at one year sits around 87%, dropping to about 80% at two years and around 59% after nearly five years. Losing effectiveness, rather than side effects, is the primary reason for stopping; about two-thirds of discontinuations were due to the drug not working well enough anymore, while roughly 27% of stops were side-effect-driven, mostly related to infections.³¹ A multicenter retrospective study spanning 152 weeks broadly confirmed that drug survival in real-world conditions was comparable to or better than what clinical trials and other real-life studies had reported.³²

Vaccinations While on Secukinumab

Because secukinumab modifies part of the immune response, people naturally wonder whether vaccines will still work. An early study in healthy volunteers found that secukinumab did not interfere with the protective response to influenza or meningococcal vaccines, and no serious adverse events were observed during the vaccination period.³³ Inactivated vaccines like the flu shot and pneumococcal vaccine are considered safe to receive during treatment. Live vaccines, however, are generally avoided while on any biologic, since the partially suppressed immune system could theoretically allow even the weakened virus in a live vaccine to cause problems. Your doctor will want to make sure you are up to date on live vaccines before you start treatment, and will guide timing if boosters come up while you are on the drug.