Determine the Effects of Gene Differences and Voriconazole on Enzyme CYP2B6 Activity in the Liver in Healthy Volunteers

Inclusion Criteria: * Male or female subject between 18 and 55 years of age. * Healthy individuals without any significant medical conditions as determined by a screening performed at University. * Adherence to the study dietary and medication restrictions. * Willingness to refrain from smoking or use of tobacco or marijuana one week before the start of the study and until completion of the study which will be a total of 17 days. * Ability to commit the time requested for this study. Exclusion Criteria: * Underweight (weighs less than 50kg or 110lb) or over weight \[body mass index (BMI) greater than 32\]. * Drug or alcohol abuse (more than 3 alcoholic drinks per day on a regular basis). * History of intolerance or allergic reaction (e.g. rash) to efavirenz and/or voriconazole. * Significant health conditions such heart, gastrointestinal disorders, liver, or kidney diseases that may be exacerbated during the course of the study. * History or current psychiatric illness (e.g. depression, anxiety, or nervousness). * History or current eye sight disturbances (e.g. blurred vision). * Serious infection within the last 2 weeks. * Blood donation within the past two months. * Screening results that do not fall in a healthy range. * Regularly taking prescriptions (except hormonal agents, e.g. oral contraceptives), over-the-counter, herbal or dietary supplements, and alternative medications and are unable or unwilling to stop taking them one week before and during the study periods. * Female with a positive pregnancy test. * Female breastfeeding. * Females of child-bearing potential who are unable or unwilling to either practice abstinence or use appropriate birth control up until the study completion, which will take a total of 17 days. * Participation in a research study involving intensive blood sampling and/or have use study drugs in the last two months. * Employed or student under supervision of any of the investigators of this study. * Inability to state a good understanding of this study including risks and requirements, and inability to follow the rules of this study.