A Research Study to Look Into How Semaglutide, Together With a Lower Dose of Insulin Glargine, Compares to a Higher Dose of Insulin Glargine Alone in People With Type 2 Diabetes (SUSTAIN OPTIMIZE)

Prior treatment

• Uncontrolled and potentially unstable diabetic retinopathy or maculopathy. Verified by a fundus examination performed within the past 90 days before screening or in the period between screening and randomisation. Pharmacological pupil-dilation is a requirement unless using a digital fundus photography camera specified for non-dilated examination.
• Any episodes of diabetic ketoacidosis within 90 days before screening.

Other illness

• Presence or history of pancreatitis (acute or chronic).

Lab values

• Potentially missed diagnosis of Type 1 diabetes (T1D) or latent autoimmune diabetes in adults (LADA) verified by C-peptide less than 0.26 nanomoles per litre (nmol/L) (or 260 picomoles per liter \[pmol/L\] \[0.78 nanograms per millilitre {ng/mL}\]) or antibodies to glutamic acid decarboxylase (anti-GAD) greater than 5 units/millilitre, as measured by the central laboratory at screening.
• Renal impairment measured as estimated Glomerular Filtration Rate (eGFR) value of less than 30 millilitre per minute per 1.73 meter square at screening as defined by Kidney Disease: Improving Global Outcomes (KDIGO) 2012 classification.

Other

• Known hypoglycaemic unawareness as indicated by the investigator according to Clarke's questionnaire question 8.

• Diagnosed with Type 2 Diabetes Mellitus (T2D) mellitus greater than or equal to (\>=) 180 days before screening.
• Glycated haemoglobin (HbA1c) of 7-10 percentage \[(53-86 millimoles per mole (mmol/mol)\] (both inclusive) as assessed by central laboratory on the day of screening.
• Body mass index (BMI) greater than or equal to (\>=) 25 kilograms per meter square (kg/m\^2) on the day of screening.
• Stable daily dose(s) greater than or equal to (\>=) 90 days before screening of any of the following anti-diabetic drugs or combination regimens:
• Any metformin formulations greater than or equal to (\>=) 1500 milligrams (mg) or maximum tolerated or effective dose.
• Any metformin combination formulation greater than or equal to (\>=) 1500 mg or maximum tolerated or effective dose.
  • The treatment can be with or without sodium glucose cotransporter 2 (SGLT-2) inhibitors.
• Treated with a once daily basal insulin (e.g. insulin glargine Unit 100 or U300, neutral protamine hagedorn (NPH) insulin, insulin detemir, insulin degludec) less than or equal to (\<=) 40 units/day (U/day) for greater than or equal to (\>=) 90 days before screening. Short-term bolus insulin treatment for a maximum of 14 days before screening is allowed.