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

The purpose of this study is to determine the maximum dose of GRT0151Y that is tolerable and to explore the safety profile of the drug. For each Treatment Period (Visits 2-5), dosing will be separated by at least one week. Participants in this study will receive up to four doses of the study drug and up to two placebo (an inactive substance) preparations, one at a time on each of up to six visits. Participants will receive a single dose of either GRT0151Y or placebo beginning with the lowest dose of study drug 150 milligrams (mg), followed by 200 mg, 250 mg, 300 mg, 350 mg and 400 mg doses of the study drug. Participants will only be allowed to proceed to the next higher dose of GRT0151Y (or placebo) if the previous dose was well tolerated. Neither the participant nor the study staff will know whether participants are receiving GRT0151Y or placebo.