A Study of TAK-105 in Healthy Adults

It is hoped that in the future, TAK-105 will be used to help treat people with nausea and vomiting. The main aims of this study are as follows: * To check for side effects from TAK-105 in healthy adults. * To learn how much TAK-105 they can receive without getting side effects from it. Participants will receive either TAK-105 as TAK-105-a or TAK-105-b (depending upon the part they are enrolled in) or a placebo as an injection under the skin (sub-cutaneous injection). A placebo looks like TAK-105-a or TAK-105-b but will not have any medicine in it. Three times as many participants will receive TAK-105-a or TAK-105-b than placebo. The study will have 6 parts. Each part will have several small groups of participants, called cohorts. Participants will only be in 1 cohort in 1 part of the study. Part 1: Participants will check into the study clinic to receive a single dose of TAK-105-a or placebo and will stay in the clinic for about 10 days. Then, participants return to the clinic for follow-up visits up to about 60 days after the dose. Part 2: Participants will check into the study clinic to receive TAK-105-a or placebo once a week for 4 weeks, and will stay in the clinic for about 26 days. Then, participants return to the clinic for follow-up visits up to about 60 days after last dose. Part 3: Participants will check into the study clinic to receive 2, 3 or 4 weekly doses of TAK-105-a or placebo. Their clinic stay will be for 10 to 24 days depending which cohort they are in. Then, participants return to the clinic for follow-up visits up to about 28 days after last dose. Part 4: Participants will check into the study clinic to receive 2 doses (once a week for 2 weeks) of TAK-105-a or placebo and will stay in the study clinic for about 12 days. They will return to the clinic later (in about 1-3 weeks) for another (third) dose and will stay for 2 days after the third dose. Then, participants return to the clinic for follow-up visits up to about 3 months after first dose. Part 5a: Participants will check into the study clinic to receive a single dose of TAK-105-a or placebo and will stay in the clinic for about 10 days. Then, participants return to the clinic for follow-up visits up to about 60 days after the dose. Part 5b: Participants will check into the study clinic to receive TAK-105-a or placebo once a week for 4 weeks, and will stay in the clinic for about 26 days. Then, participants return to the clinic for follow-up visits up to about 60 days after last dose. Part 5b will be optional, depending on the pharmacokinetic (PK) and safety data observed in Part 2. Part 6: Participants will check into the study clinic to receive a single dose of TAK-105-b or placebo and will stay in the clinic for about 10 days. Then, participants return to the clinic for follow-up visits up to about 60 days after the dose.