Semaglutide lowers blood eosinophil counts

A retrospective real-world analysis published in BMC Pulmonary Medicine on 4 July 2026 found that semaglutide treatment significantly reduced blood eosinophil counts (BECs) in 371 adults, with the proportion of participants reaching counts below 150 per microlitre rising from 44.2% at baseline to 65.8% after treatment^[1].

The study, conducted at a single centre in Shanghai, China, adds human real-world evidence to a body of laboratory and observational work suggesting that GLP-1 receptor agonists (GLP-1RAs) carry anti-inflammatory effects that extend beyond blood glucose and body weight. Eosinophils are granulocytes implicated in allergic and airway disease; elevated blood eosinophil counts are associated with worse asthma control, atopic dermatitis, and cardiovascular risk in some populations.

What the numbers show

The Shanghai team (Wu, Lin, Wu, Zhao, and colleagues) followed 371 participants who received semaglutide and measured BECs before and after treatment. The median count fell from 160 per microlitre at baseline to 110 per microlitre after treatment (P < 0.001)^[1]. Eosinophil percentage declined from 2.20% to 1.60% (P < 0.001). The reduction was seen regardless of whether participants started with high or low eosinophil counts, but baseline eosinophil level was the only independent predictor of the magnitude of reduction after adjusting for metabolic variables.

A subgroup analysis by body mass index found a more pronounced percentage reduction in participants with lower BMI: minus 31.6% in the non-obese group versus minus 21.0% in the higher-BMI group (P = 0.037). The authors registered the study prospectively in the Chinese Clinical Trial Registry under ChiCTR2500110394.

Why eosinophils matter in this context

GLP-1 receptors are present on human eosinophils, a fact established by Mitchell and colleagues in a 2017 laboratory study published in Clinical and Experimental Allergy^[2]. That work showed that a GLP-1 analog significantly reduced surface activation markers (CD11b, CD69) on eosinophils stimulated with lipopolysaccharide, and decreased eosinophil production of IL-4, IL-8, and IL-13, all cytokines relevant to allergic airway disease. The mechanistic bridge between GLP-1R signalling and eosinophil suppression has been proposed but not yet fully characterised in humans.

A 2026 review in Current Opinion in Pulmonary Medicine by O'Brien, Franciosi, and Butler at University College Dublin noted that GLP-1RAs show promise across multiple asthma phenotypes, including patients without obesity, and that modulating insulin resistance may improve asthma control independently of weight loss^[3]. The authors called for randomised controlled trials to establish mechanisms and to define where GLP-1RAs sit in asthma treatment pathways.

What this study is not

Several important cautions apply. This is a retrospective, single-centre analysis from one institution in Shanghai; external validity to other ethnic groups, clinical settings, and GLP-1RA agents is not established. The study reports median counts, not mean values, and does not report clinical outcomes such as asthma exacerbation rates, lung function, or change in inhaler use. The study covers semaglutide specifically; whether the finding applies equally to other GLP-1RAs, such as liraglutide or tirzepatide, is not answered here.

The sample size of 371 is modest for a pharmacoepidemiological study, and the absence of a parallel control group receiving a different diabetes or weight-management medicine means residual confounding cannot be ruled out. The authors themselves note that the mechanism driving the BMI-subgroup difference, the more pronounced reduction in non-obese participants, is not explained by the current data.

What we do not yet know

Several questions follow from the Wu et al. findings. First: does the eosinophil reduction translate into measurable improvements in asthma control or exacerbation frequency? A 2022 literature review in Cureus found that GLP-1RA users with asthma and concurrent diabetes experienced fewer exacerbations compared with patients on alternative diabetes medicines^[4], but that evidence base predates this real-world BEC data and comes from different study designs.

Second: is the effect durable? The Wu et al. study does not report a follow-up timepoint or what happens to eosinophil counts if semaglutide is discontinued. The durability question matters for any potential use of GLP-1RA as an eosinophil-modifying strategy in respiratory medicine. Third: the BMI interaction (larger effect in non-obese participants) is counterintuitive, given that weight loss is often assumed to mediate the anti-inflammatory benefit. That result suggests a direct drug effect that operates outside of the weight-loss pathway, but the study design cannot distinguish between those two mechanisms.

Where this fits in the semaglutide evidence base

Semaglutide is a prescription-only GLP-1 receptor agonist licensed across the EU, UK, and US for type-2 diabetes (as Ozempic and Rybelsus) and chronic weight management (as Wegovy). Its primary evidence base is the SUSTAIN programme in type-2 diabetes and the STEP programme in obesity. The SELECT trial additionally established a cardiovascular-event benefit in adults with obesity and established cardiovascular disease but without diabetes. Pulmonary and immunological effects are a newer and less settled area. For country-specific regulatory status, see our semaglutide regulation pages.

The Wu et al. study adds to a growing list of off-target observations around GLP-1RAs, a class that is producing real-world data far faster than mechanism-of-action research can explain. The eosinophil finding is plausible, supported by laboratory evidence of GLP-1R expression on eosinophils, and potentially clinically meaningful for patients with asthma who are already on semaglutide for metabolic indications. It does not yet justify starting semaglutide as an eosinophil-lowering strategy, and no regulatory agency has considered it for that purpose.