This study will have two parts. In the first part we will create eight SMART capsule-based naltrexone systems using 4 general types of pharma formulation strategies. Model naltrexone (50mg) formulations containing the GRAS taggant, 2-butanol (40 or 80 mg) will be prepared and preliminary stability studies executed. Type 1 is a hydrophobic system, Type 2 is a hydrophilic system, Type 3 is a reverse micelle system and Type 4 is a water-in-oil microemulsion system. All formulations will be prepared using USP-grade excipients, 2-butanol, naltrexone base and naltrexone HCl. Naltrexone HCl has significant water solubility and will be used in the preparation of formulation types 2 and 4, whereas the more lipid soluble free base of naltrexone will be used in formulation types 1 and 3. Manufacturer's specifications supplied by Capsugel will be used to determine compatibility between the capsule material and the proposed excipients, and will guide capsule selection (gelatin or HPMC).Prepared formulations will be characterized by particle size analysis and analyzed to determine the actual concentrations of naltrexone and 2-butanol. Particle sizing will be accomplished by dynamic light scattering using a 90Plus particle size analyzer. With formulation types 1 and 2, the technique will demonstrate the homogeneity of the mixture and the absence of particulates. With types 3 and 4, particle size distributions will be measured to confirm the presence of monodisperse reverse micelles or nanoscale droplets. The concentration of naltrexone in each final formulation will be verified by Liquid chromatography-mass spectrometry (LC-MS) and /or Ultra Performance Liquid Chromatography (UPLC). The concentration of 2-butanol will be determined by gas chromatography-Mass Spectrometry (GC-MS). Following the initial characterization, the formulations will be stored in sealed vials and placed in ICH standard stability conditions and tested at weekly intervals over 1, 3 and 6 months. The three outstanding formulation candidates will be selected to use in part two of the study.