Crohn's disease (CD) is a condition that causes swelling and irritation in the digestive system. This study is testing a new drug called TAK-279 to see if it can help reduce this inflammation compared to a placebo, which is a harmless pill with no medicine. The study will also check for any side effects, which are unwanted reactions to the medicine, and how well participants can handle these side effects. Doctors will use a test called an endoscopy to look inside the bowel to see if the drug is working.

Participants will take the medication for 52 weeks (1 year) and need to visit the study clinic 15 times. To join, participants must be between 18-75 years old, have a confirmed diagnosis of active Crohn's disease, and have tried other treatments without success. They cannot join if they have other bowel diseases, need surgery, or have certain medical devices like an ostomy bag.

• The study lasts around 60 weeks in total, including extra time for checking safety.
• Participants will be randomly given one of three doses of TAK-279 or a placebo.
• About 268 people will join this study from different places around the world.