Inhibition of 11β‐HSD1 is hypothesized to improve measures of insulin sensitivity and hepatic glucose output in patients with type II diabetes. AMG 221 is a potent, small molecule inhibitor of 11β‐HSD1. The objective of this analysis is to describe the pharmacokinetic/pharmacodynamic (PK/PD) relationship between AMG 221 and 11β‐HSD1 inhibition in ex vivo adipose tissue samples. Healthy, obese subjects were administered a single dose of 3, 30, or 100 mg of oral AMG 221 (n = 44) or placebo (n = 11). Serial blood samples were collected over 24 hours. Subcutaneous adipose tissue samples were collected by open biopsy. Population PK/PD analysis was conducted using NONMEM. The inhibitory effects (mean ± standard error of the estimate) of AMG 221 on 11β‐HSD1 activity were directly related to adipose concentrations with I_max (the maximal inhibition of 11β‐HSD1 activity) and IC₅₀ (the plasma AMG 221 concentration associated with 50% inhibition of enzyme activity) of 0.975 ± 0.003 and 1.19 ± 0.12 ng/mL, respectively. The estimated baseline 11β‐HSD1 enzyme activity was 755 ± 61 pmol/mg. An equilibration rate constant (k_eo) of 0.220 ± 0.021 h–¹ described the delay between plasma and adipose tissue AMG 221 concentrations. AMG 221 potently blocked 11β‐HSD1 activity producing sustained inhibition for the 24‐hour study duration as measured in ex vivo adipose samples. Early characterization of concentration‐response relationships can support rational selection of dose and regimen for future studies.