The study was terminated based on new safety data.

The purpose of this study is to investigate the safety and tolerability of Lu AF90103 and what the body does to Lu AF90103 after single doses of the drug administered directly into a vein.

This study is the first-in-human (FIH) study with Lu AF90103. The study is divided in two parts, Part A and Part B.

Part A is an interventional, randomized, double-blind, sequential-group, placebo-controlled, single-ascending dose study to investigate the safety, tolerability, pharmacokinetics, and pharmacodynamics of Lu AF90103 in healthy men.

Part B is an interventional, randomized, double-blind, cross-over study to investigate the safety profile after administration of Lu AF90103 as an infusion at two different rates to healthy young men.

The dosage in Part B is guided by the cohorts in Part A and is a repetition of one of the doses from Part A.

The total study duration per participant from baseline to the end of follow-up will be maximum 11 days in Part A and 16 days in Part B.

Inclusion Criteria:

• The participant is ≥18 and ≤45 years of age at the Screening Visit for Cohorts A1 to A6 (excluding cohort A2b) or ≥55 to ≤65 for participants in the CSF sampling Cohorts A2b and A7.
• The participant has body mass index (BMI) ≥18.5 kilograms (kg)/square meter (m^2) and ≤30 kg/m^2 and body weight ≥60 kilograms (kg) at the Screening Visit and at the Baseline Visit.
• The participant has a normal resting electroencephalogram (EEG) at Screening.
• The participant is, in the opinion of the investigator, generally healthy based on medical history, a physical examination, vital signs, an electrocardiogram (ECG), and the results of the clinical chemistry, haematology, urinalysis, serology, and other laboratory tests.

Exclusion Criteria:

• The participant has or has had any clinically significant immunological, cardiovascular, respiratory, metabolic, renal, hepatic, gastrointestinal, endocrinological, haematological, dermatological, venereal, neurological, or psychiatric disease or other major disorder.

Other inclusion and exclusion criteria may apply.