Nucala is not a steroid. It is a biologic medication, specifically a monoclonal antibody, that works in a completely different way than corticosteroids like prednisone. The confusion is understandable because Nucala treats many of the same conditions that steroids treat, and it’s often prescribed alongside steroids or as a way to reduce steroid use over time.
What Nucala Actually Is
Nucala (mepolizumab) belongs to a class of drugs called monoclonal antibodies. These are lab-made proteins designed to target one very specific part of the immune system. In Nucala’s case, the target is a signaling molecule called interleukin-5 (IL-5), which is the main driver behind the production and survival of eosinophils, a type of white blood cell that causes inflammation in conditions like severe asthma.
By blocking IL-5, Nucala reduces the number of eosinophils circulating in your blood and accumulating in your airways. This is a precision approach: it dials down one specific part of the immune response rather than broadly suppressing inflammation the way steroids do.
Its ingredients reflect this. Each dose contains mepolizumab (the antibody itself), along with inactive stabilizers like sucrose and sodium phosphate. There are no corticosteroid components in the formulation.
How It Differs From Steroids
Steroids like prednisone work by broadly dampening the immune system and reducing inflammation throughout the body. That wide-ranging effect is what makes them effective for so many conditions, but it’s also what produces their long list of side effects: weight gain, bone thinning, elevated blood sugar, cataracts, high blood pressure, increased infection risk, sleep problems, and mood changes like depression and anxiety. Even short courses of oral steroids are linked to higher rates of infections, bone fractures, blood clots, and gastrointestinal bleeding.
Nucala’s side effect profile looks quite different. The most commonly reported issues are headache, injection site reactions (pain, redness, or swelling where the shot is given), back pain, fatigue, and sore throat. In clinical trials, the rate of side effects in people taking Nucala was nearly identical to those on placebo (82% vs. 84%), suggesting most of those issues would have occurred regardless. The more serious but rare risks include allergic reactions and an increased chance of shingles.
Why Nucala and Steroids Are Often Used Together
If you’ve been prescribed Nucala, there’s a good chance you’re also taking inhaled or oral corticosteroids. That’s because Nucala is approved as an add-on treatment for conditions where standard therapies, including steroids, haven’t been enough on their own. It’s not typically a first-line option.
One important safety note: you should not stop taking your steroids suddenly when you start Nucala. The FDA label specifically warns against abruptly discontinuing corticosteroids and recommends tapering them gradually. This is because your body adjusts to long-term steroid use, and stopping too quickly can cause adrenal problems.
Can Nucala Help You Use Less Steroid?
This is one of the main reasons doctors prescribe Nucala. Many people with severe eosinophilic asthma depend on daily oral steroids just to keep their symptoms manageable, and the toll of long-term steroid use weighs on them. In one survey from a major clinical trial, 84% of patients said they were worried about the side effects of long-term steroid use, and 63% had already discussed those concerns with their doctor.
Clinical trials and real-world studies have shown that Nucala can allow many patients to reduce or even eliminate their oral steroid dose over time, with their doctor’s guidance. This steroid-sparing effect is a significant benefit, since even modest reductions in daily steroid intake can lower the risk of complications like bone fractures, diabetes, and weight gain.
What Nucala Is Approved to Treat
Nucala is FDA-approved for several eosinophil-driven conditions. The primary use is severe eosinophilic asthma in patients aged 6 and older. It’s also approved for eosinophilic granulomatosis with polyangiitis (EGPA), a rare condition involving inflamed blood vessels, and for chronic rhinosinusitis with nasal polyps.
The medication is given as a subcutaneous injection (a shot under the skin) once every four weeks. For asthma in adults and teens, the dose is 100 mg. Children aged 6 to 11 receive 40 mg. For EGPA, the dose is higher: 300 mg, split across three separate injections at the same visit. Some patients learn to self-inject at home using a prefilled autoinjector, while others receive the shot at a clinic.