Retinoids on CYP2D6 Activity During Pregnancy

Eligibility Details: Inclusion Criteria: - Singleton pregnancies - Extensive metabolizers Exclusion Criteria: - Chronic or persistent cough accompanying asthma, smoking or chronic obstructive pulmonary disease - Productive cough - Fever - Known kidney disease - Known liver disease - Diabetes - Obesity - Bipolar disease - Attention deficit disorder - Social phobia - Allergy or history of adverse event with dextromethorphan - Drugs, foods, beverages or dietary supplements that interact with CYP2D6 or dextromethorphan - dextromethorphan - Unable to give written informed consent - Inability to fast - Concurrent use of vitamin A supplementation