Nucala (mepolizumab) is a biologic medication approved for adults with chronic rhinosinusitis with nasal polyps who haven’t gotten enough relief from steroid nasal sprays alone. It works by targeting a specific immune signal that drives the inflammation behind polyp growth, and it’s given as an injection once every four weeks. For people stuck in a cycle of recurring polyps, congestion, and repeat surgeries, Nucala offers a way to shrink polyps and restore airflow without going back to the operating room.
How Nucala Works
Nasal polyps in chronic rhinosinusitis are driven largely by a type of white blood cell called an eosinophil. In people with this condition, eosinophils accumulate in the tissue lining the sinuses and nasal passages, triggering swelling, excess mucus, and the soft, grape-like growths that block breathing. The more active eosinophils present in polyp tissue, the worse symptoms tend to be.
Nucala blocks a protein called interleukin-5 (IL-5), which is the main signal that tells your body to produce, activate, and send eosinophils into tissues. By cutting off that signal, Nucala reduces the number of inflammatory eosinophils in nasal polyp tissue. That reduction translates directly into less swelling, less mucus-producing cell overgrowth, and smaller polyps. Research published in 2025 confirmed that the greater the drop in inflammatory eosinophils after treatment, the greater the improvement in both polyp size and quality-of-life scores.
Who Qualifies for Nucala
Nucala isn’t a first-line treatment. It’s specifically approved as an add-on for adults 18 and older who have been using nasal corticosteroid sprays and still have significant symptoms. In the clinical trials that led to FDA approval, patients had a history of prior sinus surgery and had been on nasal corticosteroids for at least eight weeks before enrollment. They also needed to meet a minimum threshold for nasal obstruction (scoring above 5 on a 10-point severity scale) and have a combined polyp score of at least 5 out of 8, with polyps visible in both nostrils.
In practice, this means Nucala is typically considered after you’ve tried corticosteroid sprays, possibly oral steroids, and potentially had at least one surgery, yet your polyps keep coming back or your symptoms remain poorly controlled.
What the Clinical Evidence Shows
The pivotal trial behind Nucala’s approval for nasal polyps, called SYNAPSE, enrolled 407 adults and followed them for a full year. Compared to placebo, patients on Nucala had significantly smaller polyps at 52 weeks and meaningfully less nasal obstruction. The nasal obstruction improvement was notable: on a 10-point scale, Nucala reduced blockage scores by about 3 additional points beyond what placebo achieved.
Beyond the numbers, patients in the trial also reported improvements in their sense of smell, postnasal drip, and overall sinus-related quality of life. A real-world study tracking patients outside of clinical trial conditions found that none of the patients on Nucala needed rescue sinus surgery during the treatment period, which is encouraging for a population that often faces repeated procedures.
How Long Before You Notice Results
Nucala is not a fast-acting medication. Expert guidelines recommend waiting four to six months before judging whether it’s working. Some people notice gradual improvement in congestion and breathing within the first few months, but the full effect on polyp size and quality of life takes time to develop. Patients who showed significant improvement in the SYNAPSE trial were assessed at the one-year mark.
If you’ve been on Nucala for six months with no noticeable change in symptoms, the likelihood of a delayed response is low. At that point, your doctor would typically reassess whether this is the right biologic for you.
What Treatment Looks Like
Nucala is a 100 mg subcutaneous injection given once every four weeks. The first dose is administered by a healthcare professional, but after that, most people learn to inject it themselves at home. It’s available as both a prefilled syringe and an autoinjector. The autoinjector hides the needle, which makes it a good option if needles bother you. In studies, 99% of patients successfully self-administered using the prefilled syringe and 89 to 95% managed the autoinjector without difficulty.
You can inject into your thigh or abdomen. If a caregiver is giving the injection, the upper arm is also an option. The injection itself is quick, and the monthly schedule means 12 clinic visits or home injections per year. Because Nucala is a maintenance treatment, you continue it long-term to keep polyps from returning.
Side Effects
Nucala has a reassuring safety profile for nasal polyp treatment. A meta-analysis pooling data from multiple biologic trials in nasal polyp patients found that the most commonly reported side effects, including headache, sore throat, nosebleeds, injection-site reactions, and common colds, occurred at essentially the same rate in patients receiving Nucala as in those receiving placebo injections. No fatal adverse events have been reported in nasal polyp trials.
The most practical concern is allergic reactions, which are rare but possible with any biologic. This is why the first injection is always given in a medical setting where you can be monitored. After that initial dose, the risk drops considerably, and home administration becomes standard.
How Nucala Compares to Surgery
Sinus surgery physically removes polyps and opens blocked sinus passages, providing immediate relief. The problem is that polyps grow back in a large percentage of patients, often within a few years. Some people end up having three, four, or more surgeries over their lifetime. Nucala addresses the underlying inflammation that causes polyps to form in the first place, which is why it can reduce the need for repeat operations.
Nucala isn’t a replacement for surgery in every case. Some patients need surgery first to clear severe obstruction, then start Nucala to prevent regrowth. Others with moderate disease may be able to avoid surgery altogether if they respond well to the biologic. The decision depends on how large your polyps are, how much they affect your breathing and smell, and how you’ve responded to previous treatments.