Arginine vasopressin (AVP) was suggested to contribute to cardiovascular risk and type 2 diabetes in patients with metabolic syndrome. The proinflammatory cytokine interleukin (IL)-1 is able to induce AVP secretion and plays a causal role in cardiovascular mortality and type 2 diabetes. We investigated in two studies whether copeptin levels – the surrogate marker for AVP – are regulated by IL-1-mediated chronic inflammation in patients with metabolic syndrome. Study A was a prospective, interventional, single-arm study (2014–2016). Study B was a randomized, placebo-controlled, double-blind study (2016–2017). n = 73 (Study A) and n = 66 (Study B) adult patients with metabolic syndrome were treated with 100 mg anakinra or placebo (only in study B) twice daily for 1 day (study A) and 28 days (study B). Fasting blood samples were drawn at day 1, 7, and 28 of treatment for measurement of serum copeptin. Patients with chronic low-grade inflammation (C-reactive protein levels ≥2 mg/L) and BMI >35 kg/m2 had higher baseline copeptin levels (7.7 (IQR 4.9–11.9) vs 5.8 (IQR 3.9–9.3) pmol/L, P inflamm = 0.009; 7.8 (IQR 5.4–11.7) vs 4.9 (IQR 3.7–9.8) pmol/L, P BMI = 0.008). Copeptin levels did not change either in the anakinra or in the placebo group and remained stable throughout the treatment (P = 0.44). Subgroup analyses did not reveal effect modifications. Therefore, we conclude that, although IL-1-mediated inflammation is associated with increased circulating copeptin levels, antagonizing IL-1 does not significantly alter copeptin levels in patients with metabolic syndrome.