Effects of Isotretinoin on CYP2D6 Activity

Inclusion Criteria: * Non-pregnant * ≥ 12 years * Patients with severe acne that are expected to receive isotretinoin for therapeutic reasons Exclusion Criteria: * Weight \< 80 lbs * Allergy or adverse reaction to dextromethorphan, vitamin A or isotretinoin * Pregnant or planning to become pregnant * Unable to follow isotretinoin risk evaluation and mitigation strategies (REMS) program (also known as iPLEDGE program) * Chronic or persistent cough accompanying asthma, smoking or chronic obstructive pulmonary disease, * Productive cough, * Fever, * Known kidney disease, * Known liver disease, * Diabetes * Obesity, body mass index ≥ 30 kg/m2 * Bipolar disease, * Attention deficit disorder, * Social phobia, * Concurrent or use within 14 days of drugs known to interact with dextromethorphan or cytochrome P450 2D6 (CYP2D6) or drugs known to increase the risk of adverse effects from dextromethorphan * Concurrent use of any other product containing dextromethorphan * Consuming foods, beverages or dietary supplements known to interact with dextromethorphan or CYP2D6 * Unable to give written informed consent/assent, * Inability to fast for 4 hours prior to study. * Wards of the State