The study compares 2 medicines for type 2 diabetes: oral semaglutide (a new medicine) and placebo (a dummy medicine). Researchers will test semaglutide to see how well it works compared to placebo. The study will also test if semaglutide is safe. Participants will either get semaglutide or placebo - which treatment is decided by chance. Participants will get 1 tablet a day to take with up to half a glass of water. Participants must take the tablet first thing in the morning on an empty stomach. After taking the tablet, participants must not eat or drink anything for at least 30 minutes. After the 30 minutes, participants can have their first meal of the day and take any other medicines they may need. The study will last for about 8 months (36 weeks). Participants will have 9 clinic visits and 2 phone calls with the study doctor. At all 9 of the clinic visits, participants will have blood samples taken. At 5 of the clinic visits, participants must arrive fasting. This means they cannot eat for 8 hours before the visit. It is fine to drink water up to 2 hours before the visit. This is for some of the blood samples that will be taken at the visit. Women cannot take part if pregnant, breastfeeding or planning to become pregnant during the study period.