We will investigate the safety and pharmacokinetics of melatonin, when administered rectally, intravesically, vaginally and transdermally. We will recruit 10 healthy female volunteers. The volunteers will have melatonin administered over 5 days; intravenously, rectally, intravesically, vaginally and transdermally. The participants will be followed for 24-48 hours with blood samples and questions about adverse events. There will be a wash-out between each session of a minimum of 7 days.

Inclusion criteria:

• Healthy female
• 20-40 years old
• BMI 18-30

Exclusion criteria:

• Inability to understand Danish, written or spoken.
• Current use of melatonin or other hypnotics/sedatives
• Current pregnancy (a positive urine-HCG; the subjects will be tested prior to each study session)
• Breast feeding
• Current alcohol or drug abuse (defined as over 5 units of alcohol per day, or any usage of illegal drugs)
• Mental illness (defined as being in medical treatment)
• Serious comorbidity (American Society of Anesthesiologists (ASA) physical status 3-4)
• Participation in other clinical trials less than 1 month prior to current study
• Night-shift work within the last 14 days prior to study
• Planned night-shift work within the study period
• Known and diagnosed sleep-disorder (defined as being in current medical treatment)
• Plasma hemoglobin <7.8 mmol/L (measured when screening participants)

They need to be female, in order to receive vaginal administration of melatonin