Naltrexone hydrochloride (NTX) and bupropion hydrochloride (BUP) (Sigma-Aldrich, St. Louis, MO) were dissolved in deionized and distilled water using sonication at 55°C. The stock solution containing drug was added to a sweetened gelatin solution comprised of berry flavored Jell-O and gelatin in distilled and deionized water. NTX and BUP, expressed as free base masses, were added to the gelatin solution to provide the following doses: 10.0 mg of NTX/3.0 ml solution/kg BW, 10.0 mg or 20.0 mg BUP/3.0 ml solution/kg BW, and 10.0 mg NTX + 10.0 mg BUP/3.0 ml solution/kg BW. While still hot, the gelatin solution containing the drug(s) was aliquoted into star shaped molds with the volume of each aliquot determined by the final concentration of the gelatin (mg drug/ml of gelatin solution) and the BW of the animal in order to produce individual drug doses, 1 dose per day per rat, as previously described (Froehlich et al., 2013a (link), 2013b (link), 2016 (link), 2017a (link), 2017b ).