A Study to Evaluate the Efficacy and Safety of TAK-906 in Adult Participants With Symptomatic Idiopathic or Diabetic Gastroparesis

The drug being tested in this study is called TAK-906. TAK-906 is being tested to treat people who have symptomatic idiopathic or diabetic gastroparesis. The study will enroll approximately 205 patients. Participants will be randomly assigned (by chance, like flipping a coin) to one of the three treatment groups (in 1:1:1:1 ratio) which will remain undisclosed to the patient and study doctor during the study (unless there is an urgent medical need): * TAK-906 Maleate 5 mg (After implementation of Amendment 8, participants will not be further randomized to this arm) * TAK-906 Maleate 25 mg * TAK-906 Maleate 50 mg Placebo (dummy inactive pill) - this is a capsule that looks like the study drug but has no active ingredient Prior to Amendment 8, participants were randomized to receive TAK-906 5 mg. After implementation of Amendment 8, participants will not be further randomized to this dose arm. All participants will be asked to take one capsule twice daily, at approximately the same time each day throughout the study. This multi-center trial will be conducted worldwide. The overall study duration is approximately 17 weeks. Participants will make multiple visits to the clinic, and will be contacted by telephone 30 days after receiving their last dose of study drug for a follow-up assessment.