The drug being tested in this study is called TAK-951. TAK-951 is being tested for prophylaxis for postoperative nausea and vomiting in high-risk participants.~The study will enroll a maximum of 160 patients, to allow a sample size of up to approximately 100 participants who have received both doses of Double-blind study drug/matching placebo. Participants will be randomly assigned in a 1:1 ratio to either Treatment Group A or Treatment Group B which will remain undisclosed to the patient and study doctor during the study (unless there is an urgent medical need):~Treatment Group A: Just before surgery, participants will receive a placebo slowly through a vein (infusion). Just before the end of the surgery, they will receive TAK-951 as an injection under the skin.~Treatment Group B: Just before surgery, participants will receive ondansetron slowly through a vein (infusion). Just before the end of the surgery, they will receive a placebo as an injection under the skin. In this study, a placebo will look like TAK-951 but will not have any medicine in it.~This trial will be conducted in the United States. The overall time to participate in the study from the time of surgery to completion is approximately 14 days. Participants will make multiple visits to the clinic and will be contacted by telephone after receiving their last dose of the drug for a follow-up assessment.
Some adults are at a higher risk of feeling sick (nausea) or being sick (vomiting) after they have surgery. In this study, these adults will have planned surgery. The main aim of this study is to learn if TAK-951 stops these adults from getting nausea or vomiting after surgery. This will be compared with another medicine called ondansetron. Another aim is to check for side effects from the study medicines.~Before surgery, the study doctor will check who can take part in this study. Those who can take part will be picked for either Treatment Group A or Treatment Group B by chance.~Treatment Group A: Just before surgery, participants will receive a placebo slowly through a vein (infusion). Just before the end of the surgery, they will receive TAK-951 as an injection under the skin.~Treatment Group B: Just before surgery, participants will receive ondansetron slowly through a vein (infusion). Just before the end of the surgery, they will receive a placebo as an injection under the skin. In this study, a placebo will look like TAK-951 but will not have any medicine in it.~Participants will not know which study medicines they received, or in which order, nor will their study doctors or surgeons. This is to help make sure the results are more reliable.~Participants will stay in the hospital for 24 hours after their surgery so that the study doctors can check for nausea and vomiting. The study doctors will also check for side effects from the study medicines.~Participants will visit the hospital for a check-up 14 days later.