Secondary obesity; Significant cardiovascular disease; Stroke, seizure disorder or other significant neurological disease; Significant liver or gallbladder disease; Significant renal disease or history of kidney stones; HIV positive status; Diabetes mellitus; Untreated or unstable hypothyroidism Malignancy in the past 5 years; Concomitant medications that cause significant weight gain or weight loss; Concomitant use of prescription or OTC weight loss medications; Had bariatric surgery or planning surgery in the next 1 year; Weight change of more than 4 kg in the past 3 months; Suicidal subjects; Major depression in the past 6 months; History of psychosis, bipolar disorder, or severe personality disorders; Subjects taking antipsychotics or mood stabilisers; Alcohol or substance abuse in the past 6 months; Currently taking zonisamide or other antiepileptic drugs; History of hypersensitivity to zonisamide or sulfonamides; Pregnant or planning pregnancy in the next year, or breastfeeding; Severe physical disability; Current participation in a commercial weight loss program or planning to participate; Currently following low-carbohydrate, high protein, high fat diet; Use of investigational medications or devices (current or past 4 weeks)