A Clinical Study in Healthy Adults Who Sometimes Take Drugs for Pleasure to Investigate the Safety and Tolerability of GRT0151Y and to Find Out Which Single Dose of the Compound is Maximally Tolerated

Inclusion Criteria: * Male or female, between 18 and 55 years of age, inclusive. * Acceptable body mass index (BMI) (weight \[kilograms\]/height (square meter) range of 19 to 30 kilograms per square meter, inclusive). * Signed an informed consent document indicating that they understand the purpose of and procedures required for the study, and are willing to participate in the study. * Participants with a history of recreational opiate use (defined as nontherapeutic use at least 10 times in the past year and at least once in the last 12 weeks prior to screening) but not dependent on opiates Diagnostic and Statistical Manual of Mental Disorders-4th edition (DSM-IV criteria). * Participants must consent to use a medically acceptable method of contraception throughout the entire study period, including washout periods. For all females of childbearing potential only: adequate contraception is defined as any form of hormonal contraception or intra-uterine device that needs to be in place for a period of at least two months prior to screening. Additional barrier contraception must be used for the duration of the study, defined as from the time of the enrolment visit to the final examination, and for at least one full month thereafter. A single barrier method alone or abstinence alone is not acceptable. Women of non-childbearing potential may be included if surgically sterile or post-menopausal for at least two years. * Female participants of childbearing potential must have a negative pregnancy test (beta- Human chorionic gonadotropin) at the enrolment visit. For females of childbearing potential, the time between the enrolment visit and first receipt of drug will be separated by a minimum of 10 days to ensure accuracy of the pregnancy test. * Participants with a positive urine drug screen (for amphetamines, barbiturates, benzodiazepines, cannabinoids, cocaine, phencyclidine and opiates) upon presentation at enrolment will be allowed to continue only if the investigator or designee considers that the presence of the drug will not introduce additional risk factors for the study participant, or interfere with study procedures or data integrity. Positive drug screens for select drugs are to be confirmed using quantitative methods such as GC/MS or equivalent, and the investigator or designee's decision to allow participants to continue will take into account the quantitative levels of drug in the subjects' urine. Participants may be rescheduled for another treatment…