A Study to Learn About the Medicine Called PF-08653944 in People With and Without Reduced Liver Function

This study is being done to learn more about an investigational medicine called PF-08653944. The goal is to understand how the body handles the medicine and to check its safety after a single dose. The study includes adults with normal liver function and adults who have mild, moderate, or severe liver problems. By comparing these groups, researchers want to understand whether liver function changes how the medicine behaves in the body. People who join the study will receive one injection of the study medicine. They will stay at the study clinic for a short time and return for follow-up visits so doctors can do blood tests, physical exams, and safety checks. This study is not expected to provide direct medical benefit to participants. The information collected will help researchers develop future treatments and understand how this medicine may be used safely in people with liver disease.

Inclusion Criteria: * Adults 18 to 75 years of age, male or female. * BMI ≥21 kg/m² and body weight \>50 kg at screening. * Group 1 (without hepatic impairment): * No known or suspected hepatic impairment. * Normal liver function tests (ALT, AST, bilirubin, albumin, PT within normal limits, with protocol-specified exceptions such as Gilbert's syndrome). * Groups 2-4 (with hepatic impairment): * Stable hepatic impairment classified as Child-Pugh Class A (mild), B (moderate), or C (severe). * No clinically significant worsening of hepatic status within 28 days prior to screening. * Women of childbearing potential must not be pregnant or breastfeeding and must agree to use highly effective contraception. Exclusion Criteria: * Clinically significant medical or psychiatric conditions, including recent or active suicidal ideation or behavior. * Use of GLP-1 receptor agonists within 90 days (or 5 half-lives) prior to dosing. * Participation in another investigational study or receipt of an investigational product within 30 days (or 5 half-lives) prior to dosing. * For hepatic-impairment groups only: * Hepatic carcinoma, hepatorenal syndrome, or limited life expectancy. * Clinically active Grade 3 or 4 hepatic encephalopathy. * Severe uncontrolled ascites, recent gastrointestinal bleeding, or history of solid organ transplant.