The purpose of this study is to determine whether 2 doses of the combination of naltrexone SR and bupropion SR are safe and effective in the treatment of obesity.

Two Phase II clinical trials have demonstrated that a combination of bupropion SR and naltrexone is associated with greater weight loss than bupropion SR alone, naltrexone alone, or placebo in subjects with uncomplicated obesity. The current study will investigate the safety and efficacy of 2 doses of the combination of naltrexone SR and bupropion SR compared to placebo in obese subjects with uncomplicated obesity and in those with obesity and hypertension and/or dyslipidemia.

• Active Comparator: Naltrexone SR 16 mg/Bupropion SR 360 mg /day
• Active Comparator: Naltrexone SR 32 mg/Bupropion SR 360 mg /day
• Placebo Comparator: Placebo

Inclusion Criteria:

• Female and male subjects, 18 to 65 years of age
• Have body mass index (BMI)of 30 to 45kg/m2 for subjects with uncomplicated obesity, and BMI of 27 to 45kg/m2 for subjects with obesity and controlled hypertension and/or dyslipidemia
• Normotensive (systolic BP < or = 140 mm Hg; diastolic < or = 90 mm Hg). Anti-hypertensive medications are allowed with the exception of alpha-adrenergic blockers, beta-blockers and clonidine. Medical regimen must be stable for at least 6 weeks prior to randomization
• Medications for treatment of dyslipidemia are allowed as long as medical regimen has been stable for at least 6 weeks prior to randomization
• Free of opioid medication for 7 days prior to randomization
• No clinically significant abnormality of serum albumin, blood urea nitrogen, creatinine, bilirubin, sodium, potassium, chloride, calcium or phosphorus
• ALT and AST within 2.5 x upper limit of normal
• No clinically significant abnormality of hematocrit, white blood cell count, white cell differential, or platelets
• Fasting glucose < 126 mg/dL on no hypoglycemic agents, fasting triglycerides < 400 mg/dL
• Negative serum pregnancy test in women of child bearing potential
• Negative urine drug screen
• If woman of child bearing potential, must be non-lactating and agree to use effective contraception throughout the study period and 30 days after discontinuation of study drug
• Able to speak and read English

Exclusion Criteria:

• Serious medical condition
• History of malignancy within the previous 5 years, with exception of non-melanoma skin cancer or surgically cured cervical cancer
• A lifetime history a serious psychiatric illness
• Current serious psychiatric illness
• In need of medications for the treatment of a psychiatric disorder (with the exception of short-term insomnia) within the previous 6 months prior to randomization
• History of drug or alcohol abuse or dependence (with the exception of nicotine dependence) within 1 year prior to study participation
• Type I or Type II diabetes mellitus
• On prohibited concomitant medications
• History of surgical or device (e.g. gastric banding) intervention for obesity
• History of seizures of any etiology, or of predisposition to seizures
• History of treatment with bupropion, or naltrexone within the preceding 12 months
• History of hypersensitivity or intolerance to bupropion or naltrexone
• Use of nicotine replacement products (nicotine gum, patch etc) during this period is excluded
• Use of drugs, herbs, or dietary supplements believed to significantly affect body weight or participation in a weight loss management program within one month prior to randomization
• Loss or gain of more than 4.0 kilograms within 3 months prior to randomization
• Pregnant or breast-feeding women or planning to become pregnant during the study period or within 30 days of discontinuing study drug