Inclusion Criteria:  Signed and dated informed consent prior to any study-mandated procedure. Willing and able to comply with study requirements. Healthy male or female adults of non-childbearing potential aged ≥ 18 and ≤ 65 years at screening. Body mass index (BMI) ≥ 18.0 and ≤ 30.0 kg/m2 at screening. Only subjects of non-childbearing potential may be included in the study. Male subjects with partners of childbearing potential must be willing to use condoms, be vasectomised or practice sexual abstinence to prevent pregnancy and drug exposure of a partner, as well as refrain from donating sperm from the date of dosing until 3 months after dosing with the IMP. Clinically acceptable medical history, physical findings, vital signs, ECG and laboratory values at the time of screening, as judged by the Investigator.  Exclusion Criteria:  Any exposure to ACD856 in the past. Treatment with another investigational drug within 3 months prior to or during the study. Positive screen for drugs of abuse or a positive alcohol result at screening or admission to the clinic. Clinically relevant findings in laboratory parameters, ECG or vital signs at screening. Current smokers or subjects who use nicotine products. History of alcohol abuse or excessive intake of alcohol. History of, or current use of, anabolic steroids. Excessive caffeine consumption. Plasma donation or blood donation prior to screening. Any planned night shift work within the duration of the study, from 48 h prior to randomisation until follow-up. Any planned major surgery within the duration of the study. Evidence of an active infection that requires treatment with antibiotics within 2 weeks of planned dosing.