The purpose of the trial is to determine if Lu AH69593 is safe and well tolerated. The trial will also look at how the body processes Lu AH69593 with and without food.

Key Inclusion Criteria:

For all participants in any trial Part (A, B, C and D):

• The participant has a resting supine pulse ≥45 and ≤100 beats per minute (bpm) at the Screening Visit and at the Baseline Visit.

Specifically for participants in trial Part A, B, and D:

• The participant has a body mass index (BMI) ≥18.5 and ≤30 kilograms (kg)/square meter (m^2) at the Screening Visit.
• The participant has a normal circadian rhythm, defined as a person who usually wakes up between 6:00 and 9:00 a.m. and goes to sleep between 9:00 p.m. and midnight.
• The participant is ≥18 and ≤55 years of age at the Screening Visit.

Specifically for participants in trial Part C:

• The participant has a BMI ≥18.5 and ≤35 kg/m^2 at the Screening Visit.
• The participant has NT1, diagnosed according to International Classification of Sleep Disorders, 3rd edition criteria, with a history of disease diagnosis >3 months prior to the Screening Visit.
• The participant is ≥18 and ≤64 years of age at the Screening Visit.

Key Exclusion Criteria:

For all participants in any trial Part (A, B, C and D):

• The participant has previously been enrolled in this trial.
• The participant has previously been dosed with Lu AH69593.
• The participant has participated in a clinical trial <30 days prior to the Screening Visit.
• The participant is pregnant, breastfeeding, intends to become pregnant, or is of childbearing potential and not willing to use adequate contraceptive methods.
• The participant has a history of cancer, other than basal cell or Stage 1 squamous cell carcinoma of the skin or adequately treated cervical intraepithelial neoplasia, that has not been in remission for >5 years prior to the first dose of investigational medicinal product (IMP).
• The participant has worked shifts, including night duty, or has travelled across >3 time zones <2 weeks prior to the first dose of IMP.
• The participant trains/exercises intensively, for example, for a marathon or triathlon, or at a competitive level.

Specifically for participants in trial Part A, B and D:

• The participant has had a clinically significant illness from which he/she recovered <4 weeks prior to the first dose of IMP.

Specifically for Participants in trial Part B and C:

• The participant is at significant risk of suicide based on medical history, mental status, investigator judgement, or the C-SSRS answer of 'yes' to suicidal ideation question 4 or 5 or 'yes' to suicidal behaviour, within the last 6 months on the C-SSRS at the Screening Visit or 'Since last visit' at the Baseline Visit Day -1.

Specifically for participants in trial Part C:

• The participant has any other disorder for which the treatment takes priority over treatment of narcolepsy or is likely to interfere with trial treatment or impair treatment compliance.
• The participant has a current medical disorder, other than NT1, associated with excessive daytime sleepiness (EDS).

Note: Other protocol-defined inclusion and exclusion criteria may apply.