Risperidone is widely used in the treatment of schizophrenia, bipolar disorder, and aggression associated with moderate or severe Alzheimer's dementia. In vitro studies have shown that constituents of tea and cola beverages can result in insoluble complex formation with risperidone, potentially reducing risperidone oral absorption. The purpose of this study is to investigate the effect of tea and cola beverage on the pharmacokinetics of risperidone oral solution.

In an open three-phase, randomized, crossover study with 12 healthy volunteers, the subjects will receive a 1 mg dose of risperidone oral solution with either water, tea or cola beverage. Blood samples will be collected and risperidone's pharmacokinetics will be monitored up to 48 hours postdose. Primary endpoint is area under the plasma concentration-time curve of risperidone.

Recruitment starting date is December 4, 2023.

Inclusion Criteria:

• Written informed consent
• Age 18-45
• Healthy
• Systolic blood pressure ≥110 mmHg
• Heart rate ≥ 50/min
• Normal ECG
• Accepted results from laboratory tests (blood haemoglobin, basic blood count and blood platelets, alanine aminotransferase, alkaline phosphatase, glutamyl transferase, creatinine, plasma potassium and sodium). Negative pregnancy test result (serum human chorionic gonadotropin) for women.

Exclusion Criteria:

• Significant disease
• Mood disorder or suicidality
• Smoking
• Using oral contraception pills or other regular medication
• Pregnancy (current or planned) or nursing
• Participation in any other studies involving investigational or marketed drug products within three months prior to the entry into this study
• Donation of blood within three months prior to the entry into this study
• Significant overweight / small or hard-to-find veins
• BMI < 18.5 kg/m2
• Insufficient Finnish language skills