1. Age 18-85 years at consent.

2. Groups:

3. Stable concomitant regimen ≥2 weeks before screening (Groups 1-2).

4. T2DM allowed if HbA1c <10% and no severe hypo/hyperglycaemia or hospitalisation within 6 months.

5. Body weight ≥50 kg; BMI 18-42 kg/m².

6. Sex assigned at birth (male/female); contraception per local regulations. Females of child bearing potential: negative pregnancy tests and condoms plus one highly effective method through 54 days post last dose. Males: condom use; no sperm donation through 54 days post last dose.

7. Written informed consent; separate consent for optional genomics.

Healthy controls only:

1. Any clinically significant disease; Diabetes;

2. lab values i) ALT/AST/ALP >1.5×ULN; ii) WBC/platelets <LLN; iii) haemoglobin <11.0 g/dL (female) or <12.0 g/dL (male); aPTT or PT/INR >1.2×ULN; iv) total bilirubin >1.5×ULN (or Gilbert's);

3. abnormal resting vital signs i) SBP >150 or <90 mmHg, ii) DBP >95 or <50 mmHg, iii) pulse ≥100 or ≤45 bpm;

4. QTcF >450 ms or clinically significant ECG abnormalities;

5. severe allergy/hypersensitivity;

6. major surgery within 30 days;

7. pancreatitis or pancreatic enzymes >2×ULN;

8. triglycerides >500 mg/dL (5.6 mmol/L);

9. calcitonin >50 ng/L (50 pg/mL);

10. severe vitamin D deficiency (<12 ng/mL, 30 nmol/L);

11. low corrected or ionised calcium;

12. HIV positive; HBV surface/core Ab or HCV Ab positive; drug/alcohol abuse within 1 year.

Hepatically impaired only:

13. Unstable medical/psychological conditions or uncontrolled systemic disease;

14. eGFR <50 mL/min/1.73 m² (CKD EPI 2021);

15. Abnormal resting vital signs i) SBP >160 or <100 mmHg, ii) DBP >110 or <65 mmHg, iii) pulse ≥100 or ≤50 bpm;

16. platelets <35×10⁹/L; neutrophils <1.2×10⁹/L; haemoglobin <85 g/L; HbA1c ≥10%;

17. oesophageal banding within 3 months or GI bleeding within 6 months;

18. ascites requiring paracentesis and albumin ≤4 week intervals; paracentesis within 30 days;

19. fluctuating/worsening hepatic function during screening; hepatocellular carcinoma;

20. acute liver disease due to infection/drug; hepatic impairment due to non liver disease;

21. biliary obstruction or non parenchymal causes; hepatic encephalopathy Grade ≥2;

22. functioning organ transplant or anticipated within 2 months; prior porto systemic shunt/TIPS;

23. QTcF >480 ms or clinically significant ECG abnormalities;

24. pancreatitis or pancreatic enzymes >2×ULN;

25. triglycerides >500 mg/dL (5.6 mmol/L); calcitonin >50 ng/L (50 pg/mL); severe vitamin D deficiency (<12 ng/mL, 30 nmol/L); ionised calcium <LLN;

26. neoplastic disease within 10 years (except adequately treated BCC/SCC or in situ cervical); MEN2 or medullary thyroid carcinoma (personal or first degree relative); significant gastric emptying abnormality;

27. HIV positive; HBV surface/core Ab or HCV Ab positive (may be included if HBV DNA or HCV RNA negative on follow up); drug/alcohol abuse within 1 year.

28. Exposure to a new chemical entity within 30 days or 5 half lives (whichever longer) before intervention; prior exposure to AZD9550 or AZD6234;

Prior/concomitant therapy:

Healthy controls:

29. use of prescription/non prescription/supplements within 7 days (or 14 days for enzyme inducers) or 5 half lives before intervention unless judged non interfering; current oral contraceptives or oestrogen HRT.

Hepatically impaired:

30. prohibited-weight loss medicines (including GLP 1), agents causing significant weight gain (e.g., systemic glucocorticoids, antipsychotics), GLP 1 RAs for diabetes, QT prolonging/prokinetic agents, oral contraceptives for contraception; restricted-short systemic glucocorticoids (≤7 days), 5HT 3 antiemetics at lowest effective dose, combined oral contraceptives for non contraceptive indications. If diabetes develops and requires insulin/SU/GLP 1 RA, discontinue from study.

Other:

31. prior enrolment in this study (screened without dosing permitted). Positive drugs of abuse and/or alcohol screen (except prescribed meds in hepatic impairment); recent blood products/donation per protocol thresholds; employees or close relatives; vulnerable populations; unlikely to comply (investigator judgement).